Crystals

14 pages, 3358 KiB

Open AccessArticle

Effect of Hot Isostatic Pressing on Mechanical Properties of K417G Nickel-Based Superalloy

by Fan Wang, Yuandong Wei, Yi Zhou, Wenqi Guo, Zexu Yang, Jinghui Jia, Shusuo Li and Haigen Zhao

Crystals 2025, 15(7), 643; https://doi.org/10.3390/cryst15070643 - 11 Jul 2025

Abstract

The cast nickel-based superalloy K417G exhibits excellent high-temperature strength, but non-equilibrium solidification during casting can cause defects such as irreparable interdendritic microporosity, which significantly degrades its fatigue and creep properties. This study uses hot isostatic pressing (HIP) to eliminate internal flaws such as [...] Read more.

The cast nickel-based superalloy K417G exhibits excellent high-temperature strength, but non-equilibrium solidification during casting can cause defects such as irreparable interdendritic microporosity, which significantly degrades its fatigue and creep properties. This study uses hot isostatic pressing (HIP) to eliminate internal flaws such as porosity in the K417G alloy, aiming to improve its mechanical properties. We investigated the microstructure and mechanical properties of K417G under two thermal conditions: solution heat treatment (SHT) and hot isostatic pressing (HIP). The results indicate that HIP significantly reduces microporosity. Compared to SHT, HIP improves the mechanical performance of K417G. The creep fracture mechanism shifts from intergranular brittle fracture (SHT) to ductile fracture (HIP). Consequently, HIP increases the alloy′s creep life approximately threefold and raises its fatigue limit by about 20 MPa. This improvement is attributed to pore density reduction, which decreases stress concentration zones and homogenizes the microstructure, thereby impeding fatigue crack nucleation and extending the crack incubation period. Full article

(This article belongs to the Special Issue Microstructure and Characterization of Crystalline Materials)

5 pages, 175 KiB

Open AccessEditorial

Characterization and Modelling of the Deformation and Failure of Engineering Metallic Materials

by Hui Wang, Lihong Su, Ebad Bagherpour and Qiang Xing

Crystals 2025, 15(7), 642; https://doi.org/10.3390/cryst15070642 - 11 Jul 2025

Abstract

Metallic materials are at the heart of modern industry and infrastructure, valued for their outstanding strength, ductility, and other excellent mechanical properties [...] Full article

(This article belongs to the Special Issue Characterization and Modelling of the Deformation and Failure of Engineering Metallic Materials)

14 pages, 828 KiB

Open AccessArticle

Investigations into Microstructure and Mechanical Properties of As-Cast Mg-Zn-xNd Alloys for Biomedical Applications

by Faruk Mert

Crystals 2025, 15(7), 641; https://doi.org/10.3390/cryst15070641 - 11 Jul 2025

Abstract

Magnesium-based biomaterials have emerged as highly promising candidates in the realm of biomedical engineering due to certain unique properties. However, their widespread application has been limited by a number of challenges, such as insufficient mechanical strength and rapid degradation rates. This study sought [...] Read more.

Magnesium-based biomaterials have emerged as highly promising candidates in the realm of biomedical engineering due to certain unique properties. However, their widespread application has been limited by a number of challenges, such as insufficient mechanical strength and rapid degradation rates. This study sought to advance the development of high-performance magnesium alloys by examining the microstructural evolution and associated strengthening mechanisms of Mg-Zn alloys modified with varying Nd contents. Comprehensive characterization techniques—including optical microscopy, XRD, and SEM/EDS—were employed to explain the influence of Nd additions on the microstructures. Mechanical performance was assessed through hardness testing, the RFDA method for elastic modulus, and tensile testing. The microstructural analysis of the as-cast Mg-Zn-Nd alloys revealed a complex phase composition comprising dendritic α-Mg, Mg₄₁Nd₅, and a Mg₃Nd binary phase enriched with rare earth elements. Notably, increasing the Nd content from 0.5% to 5% by weight resulted in a significant enhancement of hardness, reaching 59 HV compared to 42 HV in the base alloy. The tensile strength increased significantly from 62.9 MPa in the Mg-2.5Zn-0.5Nd alloy to 186.8 MPa in the Mg-2.5Zn-5Nd alloy. The elastic modulus values across all investigated alloys remained consistently comparable, which is expected as the elastic modulus is primarily determined by atomic bonding and is not significantly affected by alloying additions. These findings underscore the potential of Nd-alloyed Mg-Zn systems as viable, mechanically robust alternatives for next-generation biodegradable orthopedic implants. Full article

(This article belongs to the Special Issue Corrosion and Mechanical Performance of Magnesium Alloys)

18 pages, 1964 KiB

Open AccessArticle

Rapid Synthesis of Highly Crystalline ZnO Nanostructures: Comparative Evaluation of Two Alternative Routes

by Emely V. Ruiz-Duarte, Juan P. Molina-Jiménez, Duber A. Avila, Cesar O. Torres and Sindi D. Horta-Piñeres

Crystals 2025, 15(7), 640; https://doi.org/10.3390/cryst15070640 - 11 Jul 2025

Abstract

Zinc oxide (ZnO) is a wide bandgap semiconductor of great scientific and technological interest due to its high exciton binding energy and outstanding structural and optical properties, making it an ideal material for applications in optoelectronics, sensors, and photocatalysis. This study presents the [...] Read more.

Zinc oxide (ZnO) is a wide bandgap semiconductor of great scientific and technological interest due to its high exciton binding energy and outstanding structural and optical properties, making it an ideal material for applications in optoelectronics, sensors, and photocatalysis. This study presents the rapid synthesis of highly crystalline ZnO nanostructures using two alternative routes: (1) direct thermal decomposition of zinc acetate and (2) a physical-green route assisted by Mangifera indica extract. Both routes were subjected to identical calcination thermal conditions (400 °C for 2 h), allowing for an objective comparison of their effects on structural, vibrational, morphological, and optical characteristics. X-ray diffraction analyses confirmed the formation of a pure hexagonal wurtzite phase in both samples, highlighting a higher crystallinity index (91.6%) and a larger crystallite size (35 nm) in the sample synthesized using the physical-green route. Raman and FTIR spectra supported these findings, revealing greater structural order. Electron microscopy showed significant morphological differences, and UV-Vis analysis showed a red shift in the absorption peak, associated with a decrease in the optical bandgap (from 3.34 eV to 2.97 eV). These results demonstrate that the physical-green route promotes significant improvements in the structural and functional properties of ZnO, without requiring changes in processing temperature or the use of additional chemicals. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Oxide Nanoparticles)

20 pages, 6807 KiB

Open AccessArticle

Enhancing Electrochemical Kinetics and Stability of Biodegradable Mg-Y-Zn Alloys with LPSO Phases via Strategic Micro-Alloying with Ca, Sr, Mn, and Zr

by Lisha Wang, Huiping Wang, Chenchen Zhang, Wei Sun, Yue Wang, Lijuan Wang and Xiaoyan Kang

Crystals 2025, 15(7), 639; https://doi.org/10.3390/cryst15070639 - 11 Jul 2025

Abstract

This study systematically investigated the effects of biologically relevant microalloying elements—calcium (Ca), strontium (Sr), manganese (Mn), and zirconium (Zr)—on the electrochemical behavior of Mg-Y-Zn alloys containing long-period stacking ordered (LPSO) phases. The alloys were prepared by casting and characterized using X-ray diffraction (XRD), [...] Read more.

This study systematically investigated the effects of biologically relevant microalloying elements—calcium (Ca), strontium (Sr), manganese (Mn), and zirconium (Zr)—on the electrochemical behavior of Mg-Y-Zn alloys containing long-period stacking ordered (LPSO) phases. The alloys were prepared by casting and characterized using X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS). Electrochemical properties were assessed through potentiodynamic polarization in Hank’s solution, and corrosion rates were determined by hydrogen evolution and weight loss methods. Microalloying significantly enhanced the corrosion resistance of the base Mg-Y-Zn alloy, with corrosion rates decreasing from 2.67 mm/year (unalloyed) to 1.65 mm/year (Ca), 1.36 mm/year (Sr), 1.18 mm/year (Zr), and 1.02 mm/year (Mn). Ca and Sr additions introduced Mg₂Ca and Mg₁₇Sr₂, while Mn and Zr refined the existing LPSO structure without new phases. Sr refined the LPSO phase and formed a uniformly distributed Mg₁₇Sr₂ network, promoting uniform corrosion and suppressing deep localized attacks. Ca-induced Mg₂Ca acted as a temporary sacrificial phase, with corrosion eventually propagating along LPSO interfaces. The Mn-containing alloy exhibited the lowest corrosion rate; this is attributed to the suppression of both anodic and cathodic reaction kinetics and the formation of a stable protective surface film. Zr improved general corrosion resistance but increased susceptibility to localized attacks due to dislocation-rich zones. These findings elucidate the corrosion mechanisms in LPSO-containing Mg alloys and offer an effective strategy to enhance the electrochemical stability of biodegradable Mg-based implants. Full article

(This article belongs to the Special Issue Advances in High-Performance Alloys)

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17 pages, 5651 KiB

Open AccessArticle

Experimental Investigation on Fatigue Crack Propagation in Surface-Hardened Layer of High-Speed Train Axles

by Chun Gao, Zhengwei Yu, Yuanyuan Zhang, Tao Fan, Bo Zhang, Huajian Song and Hang Su

Crystals 2025, 15(7), 638; https://doi.org/10.3390/cryst15070638 - 11 Jul 2025

Abstract

This study examines fatigue crack growth behavior in induction-hardened S38C axle steel with a gradient microstructure. High-frequency three-point bending fatigue tests were conducted to evaluate crack growth rates (da/dN) across three depth-defined regions: a hardened layer, a heterogeneous transition [...] Read more.

This study examines fatigue crack growth behavior in induction-hardened S38C axle steel with a gradient microstructure. High-frequency three-point bending fatigue tests were conducted to evaluate crack growth rates (da/dN) across three depth-defined regions: a hardened layer, a heterogeneous transition zone, and a normalized core. Depth-resolved da/dN–ΔK relationships were established, and Paris Law parameters were extracted. The surface-hardened layer exhibited the lowest crack growth rates and flattest Paris slope, while the transition zone showed notable scatter due to microstructural heterogeneity and residual stress effects. These findings provide experimental insight into the fatigue performance of gradient-structured axle steels and offer guidance for fatigue life prediction and inspection planning. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Crystalline Metal Structures)

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19 pages, 2624 KiB

Open AccessArticle

The Modeling of Electromagnetic Behavior in the High-Frequency Range of Al₂O₃ and TiO₂ Thermoplastic Composites in Support of Developing New Substrates for Flexible Electronics

by Radu F. Damian, Cristina Pachiu, Alexandra Mocanu, Alexandru Trandabat and Romeo Cristian Ciobanu

Crystals 2025, 15(7), 637; https://doi.org/10.3390/cryst15070637 - 10 Jul 2025

Abstract

The paper describes the simulation of energy absorption in polymer micro-composites that include dielectric inserts (commercial Al₂O₃ and TiO₂ particles, with three particle sizes of 1, 5 and 25 µm, respectively). The investigated frequency spectrum, mainly from 0.001 to [...] Read more.

The paper describes the simulation of energy absorption in polymer micro-composites that include dielectric inserts (commercial Al₂O₃ and TiO₂ particles, with three particle sizes of 1, 5 and 25 µm, respectively). The investigated frequency spectrum, mainly from 0.001 to 100 GHz, is designed for various uses as substrates in electronic technologies. The electromagnetic simulation software chosen was CST Studio Suite, which evaluates the power loss at different frequencies, playing a crucial role in creating the ideal structure of these substrates. The effective limits of the electromagnetic simulation are specified. It is shown that a considerable increase in absorption occurs, by a factor of 12 to 120, depending on the dielectric material used for the inserts and the mass ratio applied in the insertion technique. Dielectrics with high permittivity provide higher absorption, but also create a nonuniform field distribution within the material, resulting in a high peak-to-average absorption ratio. In scenarios where this behavior is intolerable, the technology must be carefully tuned to improve the consistency of the insertions in the substrate material. The final outcomes of the simulations indicated that for creating new substrates for flexible electronics, polyethylene composites with TiO₂ insertions are suggested, particularly at lower concentrations of up to 7% and with a larger radius, such as 25 μm, which could offer significant economic advantages considering that the current concept advises the use of costly particles ranging from nanoscale particles to those 1 μm in size and a composition exceeding 10%. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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19 pages, 5941 KiB

Open AccessArticle

Non-Calcined Metal Tartrate Pore Formers for Lowering Sintering Temperature of Solid Oxide Fuel Cells

by Mehdi Choolaei, Mohsen Fallah Vostakola and Bahman Amini Horri

Crystals 2025, 15(7), 636; https://doi.org/10.3390/cryst15070636 - 10 Jul 2025

Abstract

This paper investigates the application of non-calcined metal tartrate as a novel alternative pore former to prepare functional ceramic composites to fabricate solid oxide fuel cells (SOFCs). Compared to carbonaceous pore formers, non-calcined pore formers offer high compatibility with various ceramic composites, providing [...] Read more.

This paper investigates the application of non-calcined metal tartrate as a novel alternative pore former to prepare functional ceramic composites to fabricate solid oxide fuel cells (SOFCs). Compared to carbonaceous pore formers, non-calcined pore formers offer high compatibility with various ceramic composites, providing better control over porosity and pore size distribution, which allows for enhanced gas diffusion, reactant transport and gaseous product release within the fuel cells’ functional layers. In this work, nanocrystalline gadolinium-doped ceria (GDC) and Ni-Gd-Ce-tartrate anode powders were prepared using a single-step co-precipitation synthesis method, based on the carboxylate route, utilising ammonium tartrate as a low-cost, environmentally friendly precipitant. The non-calcined Ni-Gd-Ce-tartrate was used to fabricate dense GDC electrolyte pellets (5–20 μm thick) integrated with a thin film of Ni-GDC anode with controlled porosity at 1300 °C. The dilatometry analysis showed the shrinkage anisotropy factor for the anode substrates prepared using 20 wt. The percentages of Ni-Gd-Ce-tartrate were 30 wt.% and 40 wt.%, with values of 0.98 and 1.01, respectively, showing a significant improvement in microstructural properties and pore size compared to those fabricated using a carbonaceous pore former. The results showed that the non-calcined pore formers can also lower the sintering temperature for GDC to below 1300 °C, saving energy and reducing thermal stresses on the materials. They can also help maintain optimal material properties during sintering, minimising the risk of unwanted chemical reactions or contamination. This flexibility enables the versatile designing and manufacturing of ceramic fuel cells with tailored compositions at a lower cost for large-scale applications. Full article

(This article belongs to the Section Materials for Energy Applications)

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14 pages, 2811 KiB

Open AccessArticle

A Silicon Complex of 1,4,7,10-Tetraazacyclododecane (Cyclen) with Unusual Coordination Geometry

by Uwe Böhme, Marcus Herbig and Betty Günther

Crystals 2025, 15(7), 635; https://doi.org/10.3390/cryst15070635 - 10 Jul 2025

Abstract

[1,4,7,10-Tetraazacyclododecano-κ⁴N^1,4,7,10(3-)]silicon(IV) chloride was synthesized from 1,4,7,10-tetraazacyclododecane (cyclen), n-butyl lithium, and silicon tetrachloride. The crystal structure analysis reveals that this cationic compound is a dimer in the solid state with pentacoordinate silicon atoms. The compound was characterized by melting [...] Read more.

[1,4,7,10-Tetraazacyclododecano-κ⁴N^1,4,7,10(3-)]silicon(IV) chloride was synthesized from 1,4,7,10-tetraazacyclododecane (cyclen), n-butyl lithium, and silicon tetrachloride. The crystal structure analysis reveals that this cationic compound is a dimer in the solid state with pentacoordinate silicon atoms. The compound was characterized by melting point, IR, and NMR spectroscopy. The quantum chemical analysis shows that this compound might be an interesting precursor to generate a mononuclear silicon (IV) complex with unusual reactivity due to nearly planar tetracoordinate coordination geometry at the silicon atom. Full article

(This article belongs to the Section Macromolecular Crystals)

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9 pages, 2121 KiB

Open AccessArticle

Using Second-Harmonic Generation Microscopy Images of Bee Honey Crystals to Detect Fructose Adulteration

by Manuel H. De la Torre-I, J. M. Flores-Moreno, C. Frausto-Reyes and Rafael Casillas-Peñuelas

Crystals 2025, 15(7), 634; https://doi.org/10.3390/cryst15070634 - 10 Jul 2025

Abstract

Second-harmonic generation microscopy is applied to mesquite honey samples with different fructose adulteration concentrations. As a proof of principle, mesquite honey is selected for this test, as it has a monofloral and spreadable-like-butter consistency, besides its economic relevance in the central region of [...] Read more.

Second-harmonic generation microscopy is applied to mesquite honey samples with different fructose adulteration concentrations. As a proof of principle, mesquite honey is selected for this test, as it has a monofloral and spreadable-like-butter consistency, besides its economic relevance in the central region of Mexico. Second-harmonic generation microscopy is an optical method that images microstructures, such as sugar crystals in bee honey, without the interference of the liquid phase. Each recorded image is spectrally registered using the photomultiplier detector of the microscope, resulting in several gray-level histograms that are numerically analyzed using signal and image processing techniques. Several samples are prepared, adulterated, and analyzed for this purpose. The inspection requires only a microscopic amount of honey, making it a suitable technique for rare and exotic honey samples that are harvested in limited quantities. The analysis of the experimental results reveals that the second-harmonic generation microscopy signal is sensitive to liquid fructose adulteration in honey, with its signal decreasing as the amount of added fructose increases. Full article

(This article belongs to the Section Industrial Crystallization)

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16 pages, 1918 KiB

Open AccessArticle

Optimization of In_xGa_1−xN P-I-N Solar Cells: Achieving 21% Efficiency Through SCAPS-1D Modeling

by Hassan Abboudi, Walid Belaid, Redouane En-nadir, Ilyass Ez-zejjari, Mohammed Zouini, Ahmed Sali and Haddou El Ghazi

Crystals 2025, 15(7), 633; https://doi.org/10.3390/cryst15070633 - 9 Jul 2025

Abstract

This study provides an in-depth numerical simulation to optimize the structure of InGaN-based p-i-n single homojunction solar cells using SCAPS-1D software. The cell comprised a p-type

{I n}_{0.6} {G a}_{0.4} N

layer, an intrinsic i-type [...] Read more.

This study provides an in-depth numerical simulation to optimize the structure of InGaN-based p-i-n single homojunction solar cells using SCAPS-1D software. The cell comprised a p-type

{I n}_{0.6} {G a}_{0.4} N

layer, an intrinsic i-type

{I n}_{0.52} {G a}_{0.48} N

layer, and an n-type

{I n}_{0.48} {G a}_{0.52} N

layer. A systematic parametric optimization methodology was employed, involving a sequential investigation of doping concentrations, layer thicknesses, and indium composition to identify the optimal device configuration. Initial optimization of doping levels established optimal concentrations of

N_{d} = 1 \times 10^{16} {c m}^{- 3}

for the p-layer and

N_{a} = 8 \times 10^{17} {c m}^{- 3}

for the n-layer. Subsequently, structural parameters were optimized through systematic variation of layer thicknesses while maintaining optimal doping concentrations. The comprehensive optimization culminated in the identification of an optimal device architecture featuring a p-type layer thickness of 0.2 μm, an intrinsic layer thickness of 0.4 μm, an n-type layer thickness of 0.06 μm, and an indium composition of x = 0.59 in the intrinsic layer. This fully optimized configuration achieved a maximum conversion efficiency (η) of 21.40%, a short-circuit current density (

J_{s c}

) of 28.2 mA/cm², and an open-circuit voltage (

V_{o c}

) of 0.874 V. The systematic optimization approach demonstrates the critical importance of simultaneous parameter optimization in achieving superior photovoltaic performance, with the final device configuration representing a 30.01% efficiency improvement compared to the baseline structure. These findings provide critical insights for improving the design and performance of InGaN-based solar cells, serving as a valuable reference for future experimental research. Full article

(This article belongs to the Section Materials for Energy Applications)

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15 pages, 1120 KiB

Open AccessArticle

Effects of Preheating on the Mechanical Properties of Dental Composites

by Maher S. Hajjaj, Lama F. Alhowirini, Raneem S. Alghamdi, Yasser M. Merdad, Hanan K. Filemban, Marwa Bawazir, Khawlah A. Alothman, Najla Al Turkestani and Saeed J. Alzahrani

Crystals 2025, 15(7), 632; https://doi.org/10.3390/cryst15070632 - 9 Jul 2025

Abstract

The aim of this study was to evaluate the mechanical properties (flexural strength (FS), flexural modulus (FM), Vickers microhardness (VMN), and shear bond strength (SBS)) of preheated composites. Two preheated composites (Z350XT and Proclinic) and one self-adhesive resin cement (RelyX™ U200) were used [...] Read more.

The aim of this study was to evaluate the mechanical properties (flexural strength (FS), flexural modulus (FM), Vickers microhardness (VMN), and shear bond strength (SBS)) of preheated composites. Two preheated composites (Z350XT and Proclinic) and one self-adhesive resin cement (RelyX™ U200) were used to fabricate specimens. All the specimens were subjected to thermocycling before their mechanical properties were evaluated. One-way ANOVA was used for statistical analysis, followed by Tukey’s post hoc test. The chi-square test was used to evaluate the failure modes after SBS test. Results: RelyX™ U200 had a significantly higher FS (106.22 ± 14.23 MPa) than Proclinic (85.76 ± 12.75 MPa) and Z350 (71.47 ± 22.98 MPa). Z350 (118.10 ± 11.3 GPa) and RelyX™ U200 (110.88 ± 13.44 GPa) had significantly higher FMs than Proclinic (83.72 ± 9.3 GPa). A significantly higher VHN was seen with Z350 (136.84 ± 11.52 VHN) compared to Proclinic (115.25 ± 17.15 VHN) and RelyX™ U200 (100.83 ± 12.69 VHN). Z350 had a higher SBS (20.75 ± 5.6 MPa) than RelyX™ U200 (15.4 ± 3.46 MPa), while Proclinic was the weakest among all the groups (6.76 ± 1.44 MPa). In the failure mode analysis, the mixed failure mode was predominantly seen in all groups. In conclusion, not all preheated composites behave the same and it is the clinician’s responsibility to select the appropriate material for every clinical situation. Full article

(This article belongs to the Special Issue Structural and Characterization of Composite Materials)

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14 pages, 1991 KiB

Open AccessArticle

Chemical Manipulation of the Collective Superspin Dynamics in Heat-Generating Superparamagnetic Fluids: An AC-Susceptibility Study

by Cristian E. Botez and Alex D. Price

Crystals 2025, 15(7), 631; https://doi.org/10.3390/cryst15070631 - 9 Jul 2025

Abstract

We use Co doping to alter the magnetic relaxation dynamics in superparamagnetic nanofluids made of 18 nm average diameter Fe₃O₄ nanoparticles immersed in Isopar M. Ac-susceptibility data recorded at different frequencies and temperatures, χ″vs. T|_f, reveals a major [...] Read more.

We use Co doping to alter the magnetic relaxation dynamics in superparamagnetic nanofluids made of 18 nm average diameter Fe₃O₄ nanoparticles immersed in Isopar M. Ac-susceptibility data recorded at different frequencies and temperatures, χ″vs. T|_f, reveals a major (~100 K) increase in the superspin blocking temperature of the Co_0.2Fe_2.8O₄-based fluid (CFO) compared to its Fe₃O₄ counterpart (FO). We ascribe this behavior to the strengthening of the interparticle magnetic dipole interactions upon Co doping, as demonstrated by the relative χ″-peak temperature variation per frequency decade

Φ = \frac{∆ T}{T \cdot ∆ l o g (f)}

, which decreases from Φ~0.15 in FO to Φ~0.025 in CFO. In addition, χ″vs. T|_f datasets from the CFO fluid reveal two magnetic events at temperatures T_p1 = 240 K and T_p2 = 275 K, both above the fluid’s freezing point (T_F = 197 K). We demonstrate that the physical rotation of the nanoparticles within the fluid, the Brown mechanism, is entirely responsible for the collective superspin relaxation observed at T_p1, whereas the Néel mechanism, the superspin flip across an energy barrier within the particle, is dominant at T_p2. We confirm this finding through fits of models that describe the temperature dependence of the relaxation time via the two mechanisms:

τ_{B} (T) = \frac{3 η_{0} V_{H}}{k_{B} T} \exp [\frac{E^{'}}{k_{B} (T - {T_{0}}^{'})}]

and

τ_{N} (T) = τ_{0} \exp [\frac{E_{B}}{k_{B} (T - T_{0})}]

. The best fits yield

γ_{0} = \frac{3 η_{0} V_{H}}{k_{B}}

= 1.5 × 10⁻⁸ s·K, E′/k_B = 7 03 K, and T₀′ = 201 K for the Brown relaxation, and E_B/k_B = 2818 K and T₀ = 143 K for the Néel relaxation. Full article

(This article belongs to the Special Issue Innovations in Magnetic Composites: Synthesis to Application)

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11 pages, 7411 KiB

Open AccessArticle

The Effects of Thermo-Mechanical Treatments on Microstructure and High-Temperature Mechanical Properties of a Nickel-Based Superalloy

by Zihan Kang, Yaxing Ma and Qian Lei

Crystals 2025, 15(7), 630; https://doi.org/10.3390/cryst15070630 - 9 Jul 2025

Abstract

The effects of thermo-mechanical treatment and different annealing temperatures on the microstructure and mechanical properties of a nickel-based superalloy were investigated by metallographic microscope, scanning electron microscope, and mechanical properties measurements. The results demonstrated that the tensile strength and elongation of the hot-rolled [...] Read more.

The effects of thermo-mechanical treatment and different annealing temperatures on the microstructure and mechanical properties of a nickel-based superalloy were investigated by metallographic microscope, scanning electron microscope, and mechanical properties measurements. The results demonstrated that the tensile strength and elongation of the hot-rolled samples were higher than those of the annealed ones. The ultimate engineering stress and engineering strain of the studied samples solid solution treated at 1175 °C for 4 h were 709 ± 19.8 MPa and 87.2 ± 1.4%, and the product of strength times elongation (PSE) was 61.8 GPa·%. These findings indicated that the thermo-mechanical treatment was an effective method to improve both the strength and the ductility of the nickel-based superalloy. Full article

(This article belongs to the Special Issue Emerging Topics of High-Performance Alloys (2nd Edition))

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15 pages, 4738 KiB

Open AccessArticle

Mechanical Performance of Ceria-Coated 3D-Printed Black Zirconia Cellular Structures After Solar Thermochemical CO/H₂ Fuel Production Cycles

by Fernando A. Costa Oliveira, Manuel Sardinha, Joaquim M. Justino Netto, Miguel Farinha, Marco Leite, M. Alexandra Barreiros, Stéphane Abanades and Jorge Cruz Fernandes

Crystals 2025, 15(7), 629; https://doi.org/10.3390/cryst15070629 - 8 Jul 2025

Viewed by 39

Abstract

Solar fuels production requires developing redox active materials with porous structures able to withstand thermochemical cycles with enhanced thermal stability under concentrated solar irradiation conditions. The mechanical performance of 3D-printed, macroporous black zirconia gyroid structures, coated with redox-active ceria, was assessed for their [...] Read more.

Solar fuels production requires developing redox active materials with porous structures able to withstand thermochemical cycles with enhanced thermal stability under concentrated solar irradiation conditions. The mechanical performance of 3D-printed, macroporous black zirconia gyroid structures, coated with redox-active ceria, was assessed for their suitability in solar thermochemical cycles for CO₂ and H₂O splitting. Experiments were conducted using a 1.5 kW solar furnace to supply the high-temperature concentrated heat to a windowed reaction chamber to carry out thermal redox cycling under realistic on-sun conditions. The ceria coating on ceramic structures improved the thermal stability and redox efficiency while minimizing the quantity of the redox material involved. Crushing strength measurements showed that samples not directly exposed to the concentrated solar flux retained their mechanical performance after thermal cycling (~10 MPa), while those near the concentrated solar beam focus exhibited significant degradation due to thermal stresses and the formation of Ce_xZr_1−xO₂ solid solutions (~1.5 MPa). A Weibull modulus of 8.5 was estimated, marking the first report of such a parameter for fused filament fabrication (FFF)-manufactured black zirconia with gyroid architecture. Failure occurred via a damage accumulation mechanism at both micro- and macro-scales. These findings support the viability of ceria-coated cellular ceramics for scalable solar fuel production and highlight the need for optimized reactor designs. Full article

(This article belongs to the Section Materials for Energy Applications)

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18 pages, 5983 KiB

Open AccessArticle

Fixed Particle Size Ratio Pure Copper Metal Powder Molding Fine Simulation Analysis

by Yuanbo Zhao, Mengyao Weng, Wenchao Wang, Wenzhe Wang, Hui Qi and Chongming Li

Crystals 2025, 15(7), 628; https://doi.org/10.3390/cryst15070628 - 5 Jul 2025

Viewed by 138

Abstract

In this paper, a discrete element method (DEM) coupled with a finite element method (FEM) was used to elucidate the impact of packing structures and size ratios on the cold die compaction behavior of pure copper powders. HCP structure, SC structure, and three [...] Read more.

In this paper, a discrete element method (DEM) coupled with a finite element method (FEM) was used to elucidate the impact of packing structures and size ratios on the cold die compaction behavior of pure copper powders. HCP structure, SC structure, and three random packing structures with different particle size ratios (1:2, 1:3, and 1:4) were generated by the DEM, and then simulated by the FEM to analyze the average relative density, von Mises stress, and force chain structures of the compact. The results show that for HCP and SC structures with a regular stacking structure, the average relative densities of the compact were higher than those of random packing structures, which were 0.9823, 0.9693, 0.9456, 0.9502, and 0.9507, respectively. Compared with their initial packing density, it could be improved by up to 21.13%. For the bigger particle in HCP and SC structures, the stress concentration was located between the adjacent layers, while in the small particles, it was located between contacted particles. During the initial compaction phase, smaller particles tend to occupy the voids between larger particles. As the pressure increases, larger particles deform plastically in a notable way to create a stabilizing force chain. This action reduces the axial stress gradient and improves radial symmetry. The transition from a contact-dominated to a body-stress-dominated state is further demonstrated by stress distribution maps and contact force vector analysis, highlighting the interaction between particle rearrangement and plasticity. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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17 pages, 2576 KiB

Open AccessArticle

Discovery and Structural Characterization of a Novel Polymorph (Form III) of Alclometasone Dipropionate

by Gianfranco Lopopolo, M. Giovanna E. Papadopoulos, Corrado Cuocci, Giuseppe F. Mangiatordi, Antonio Lopalco, Emanuele Attolino and Rosanna Rizzi

Crystals 2025, 15(7), 627; https://doi.org/10.3390/cryst15070627 - 5 Jul 2025

Viewed by 103

Abstract

This study reports the discovery and structural characterization of a novel polymorph, designated as Form III, of Alclometasone dipropionate, a corticosteroid commonly used in the treatment of inflammatory dermatoses. Form III was obtained by modifying the crystallization conditions reported in prior art and [...] Read more.

This study reports the discovery and structural characterization of a novel polymorph, designated as Form III, of Alclometasone dipropionate, a corticosteroid commonly used in the treatment of inflammatory dermatoses. Form III was obtained by modifying the crystallization conditions reported in prior art and was thoroughly characterized using Powder X-ray Diffraction (PXRD), Fourier Transform Infrared (FT-IR) spectroscopy, melting-point determination, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), including its first derivative (DTG), optical microscopy, and Scanning Electron Microscopy (SEM). In parallel, pure Form II, previously observed only in mixtures with Form I, was successfully isolated and characterized using the same analytical techniques. Both forms were compared in terms of structural, thermal, and morphological properties. PXRD analysis revealed that Form III crystallizes in a triclinic system; FT-IR spectroscopy revealed unique vibrational signatures, and microscopy showed rod-like crystal morphology. The discovery of Form III expands the current understanding of the solid-state landscape of Alclometasone dipropionate and opens opportunities for the identification of new industrial purification methods for the compound. Full article

(This article belongs to the Special Issue Celebrating the 10th Anniversary of International Crystallography)

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24 pages, 7448 KiB

Open AccessArticle

A Novel Approach to Quantitatively Account on Deposition Efficiency by Direct Energy Deposition: Case of Hardfacing-Coated AISI 304 SS

by Gabriele Grima, Kamal Sleem, Alberto Santoni, Gianni Virgili, Vincenzo Foti, Marcello Cabibbo and Eleonora Santecchia

Crystals 2025, 15(7), 626; https://doi.org/10.3390/cryst15070626 - 5 Jul 2025

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Abstract

Nickel-based coatings have been demonstrated to effectively enhance the surface performance of stainless-steel components. The present study investigates the deposition efficiency and quality of Colmonoy 227-F nickel alloy coatings on AISI 304 stainless steel using direct energy deposition (DED). The work focuses on [...] Read more.

Nickel-based coatings have been demonstrated to effectively enhance the surface performance of stainless-steel components. The present study investigates the deposition efficiency and quality of Colmonoy 227-F nickel alloy coatings on AISI 304 stainless steel using direct energy deposition (DED). The work focuses on the relationships between process parameters, microstructural features, and mechanical properties. A total of sixteen process parameter combinations were studied, varying laser power and scanning speed to establish optimal deposition conditions and to evaluate coating morphology, surface topology, dilution behavior, and mechanical performance. The surface geometry was analyzed using three-dimensional digital confocal microscopy. New material distribution (MD) indices were developed to quantify spatial uniformity and integrity of single coating scan tracks (CSTs) across the XY, XZ, and YZ planes. The optimal process was identified around 900 W laser power, balancing deposition efficiency and structural integrity. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) reveal a gradual compositional transition between coating and substrate. The results of the microhardness test demonstrate a consistent gradient in mechanical properties, extending from the coating to the substrate. Coatings were found to achieve a hardness level of up to 600 HK. These findings establish a new benchmark for evaluating DED high-performance coatings and offer a scalable methodology for optimizing additive manufacturing processes in surface engineering applications. Full article

(This article belongs to the Special Issue Recent Advances in Microstructure and Properties of Metals and Alloys)

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13 pages, 11057 KiB

Open AccessArticle

Microstructure, Hardness and Tribological Characteristics of High-Entropy Coating Obtained by Detonation Spraying

by Zhuldyz Sagdoldina, Laila Sulyubayeva, Dastan Buitkenov and Yedilzhan Kambarov

Crystals 2025, 15(7), 625; https://doi.org/10.3390/cryst15070625 - 4 Jul 2025

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Abstract

In this study, powders based on a high-entropy AlCoCrFeNi alloy obtained by mechanical alloying were successfully applied to a 316L stainless steel substrate by detonation spraying under various conditions. Their microstructural features, phase composition, hardness, and wear resistance were studied. A comparative analysis [...] Read more.

In this study, powders based on a high-entropy AlCoCrFeNi alloy obtained by mechanical alloying were successfully applied to a 316L stainless steel substrate by detonation spraying under various conditions. Their microstructural features, phase composition, hardness, and wear resistance were studied. A comparative analysis between the initial powder and the coatings was performed, including phase transformation modeling using Thermo-Calc under non-equilibrium conditions. The results showed that the phase composition of the powder and coatings includes body-centered cubic lattice (BCC), its ordered modification (B2), and face-centered cubic lattice FCC phases, which is consistent with the predictions of the Scheil solidification model, describing the process of non-equilibrium solidification, assuming no diffusion in the solid phase and complete mixing in the liquid phase. Rapid solidification and high-speed impact deformation of the powder led to significant grain refinement in the detonation spraying coating, which ultimately improved the mechanical properties at the micro level. The data obtained demonstrate the high efficiency of the AlCoCrFeNi coating applied by detonation spraying and confirm its potential for use in conditions of increased wear and mechanical stress. AlCoCrFeNi coatings may be promising for use as structural materials in the future. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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16 pages, 4823 KiB

Open AccessArticle

Magnetic Behavior of Co²⁺-Doped NiFe₂O₄ Nanoparticles with Single-Phase Spinel Structure

by Fatemeh Vahedrouz, Mehdi Alizadeh, Abbas Bahrami and Farnaz Heidari Laybidi

Crystals 2025, 15(7), 624; https://doi.org/10.3390/cryst15070624 - 4 Jul 2025

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Abstract

This study reports the synthesis and characterization of Co_xNi_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) nanoparticles using a co-precipitation method. In this approach, metal ions are precipitated in the presence of a stabilizing agent, [...] Read more.

This study reports the synthesis and characterization of Co_xNi_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) nanoparticles using a co-precipitation method. In this approach, metal ions are precipitated in the presence of a stabilizing agent, which is a common and effective method for nanoparticle preparation. The microstructure and magnetic properties were studied after calcination at 600 °C and heat treatment at 1000 °C. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy confirmed the formation of a single-phase spinel structure. The average crystallite size, calculated using the (311) diffraction peak and the Scherrer equation, ranged from 13 to 19 nm. Scanning electron microscopy (SEM) showed that the nanoparticles had a spherical morphology. Thermogravimetric and differential thermal analysis (TG-DTA) revealed a three-step weight loss process. Magnetic measurements, including remanent magnetization, saturation magnetization, and coercivity, were performed using a vibrating sample magnetometer (VSM) at room temperature. The replacement of Ni²⁺ with Co²⁺ enhanced the magnetic properties, resulting in increased magnetic moment and anisotropy. These effects are attributed to changes in cation distribution, exchange interactions, surface effects, and magnetocrystalline anisotropy. Overall, Co²⁺ doping improved the magnetic behavior of nickel ferrite, indicating its potential for application in memory devices and magnetic recording media. Full article

(This article belongs to the Special Issue Polycrystalline Materials—from Microstructure Characterization to Applications)

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9 pages, 1701 KiB

Open AccessArticle

Effects of [Zn_0.5Si_0.5]³⁺ Substitution on Microwave Dielectric Properties of ZnAl_2-x(Zn_0.5Si_0.5)_xO₄ Ceramics

by Xuekai Lan, Bairui Chen, Huatao Tang, Changzhi Yin, Bin Tian and Wen Lei

Crystals 2025, 15(7), 623; https://doi.org/10.3390/cryst15070623 - 4 Jul 2025

Viewed by 118

Abstract

Microwave dielectric ceramics are indispensable in modern communication technologies, playing a pivotal role in components such as filters, oscillators, and antennas. Among these materials, ZnAl₂O₄ ceramics have garnered attention for their excellent quality factor (Q × f) and [...] Read more.

Microwave dielectric ceramics are indispensable in modern communication technologies, playing a pivotal role in components such as filters, oscillators, and antennas. Among these materials, ZnAl₂O₄ ceramics have garnered attention for their excellent quality factor (Q × f) and low dielectric constant (ε_r). However, their high sintering temperature (~1650 °C) limits practical applications. This study investigates ZnAl_2-x(Zn_0.5Si_0.5)_xO₄ (ZAZS) (x = 0.1–0.9) ceramics, where [Zn_0.5Si_0.5]³⁺ substitutes Al³⁺, to reduce sintering temperature while maintaining high-performance microwave dielectric properties. ZAZS ceramics were synthesized via the solid-state reaction method and characterized for their structural, morphological, and dielectric properties. X-ray diffraction analysis confirmed the formation of a single-phase solid solution up to x = 0.8, with minor secondary phases appearing at x = 0.9. The substitution increased lattice parameters and enhanced material densification, as observed through SEM and relative density calculations. Microwave dielectric measurements showed that ZAZS ceramics achieved a maximum Q × f of 20,200 GHz and a τ_f value reduced to −62 ppm/°C at x = 0.8, while ε_r decreased from 7.90 to 6.98. Bond-valence calculations reveal that the reduction of the average Al/Zn/Si–O bond valence weakens octahedral rigidity, systematically tuning τ_f toward zero. These results demonstrate that ZAZS ceramics, with a reduced sintering temperature of 1400 °C, exhibit excellent potential for application in low-loss microwave devices. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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9 pages, 2068 KiB

Open AccessArticle

Effects of Ge-Doping on Thermoelectric Performance of Polycrystalline Cubic Sn_0.5Ag_0.25Bi_0.25Se_0.50Te_0.50

by Haoyu Zhao, Junliang Zhu, Zhonghe Zhu, Lin Bo, Wenying Wang, Xingshuo Liu, Changcun Li and Degang Zhao

Crystals 2025, 15(7), 622; https://doi.org/10.3390/cryst15070622 - 4 Jul 2025

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Abstract

Cubic phase SnSe-based materials have great potential in the field of thermoelectricity due to their reduced carrier scattering, increased band degeneracy, and ultra-low lattice thermal conductivity. Nevertheless, systematic studies on the influence of element doping on the thermoelectric properties of cubic SnSe-based materials [...] Read more.

Cubic phase SnSe-based materials have great potential in the field of thermoelectricity due to their reduced carrier scattering, increased band degeneracy, and ultra-low lattice thermal conductivity. Nevertheless, systematic studies on the influence of element doping on the thermoelectric properties of cubic SnSe-based materials are still relatively scarce. To enrich the research in this field, this work investigates the effects of Ge doping on the phase composition, electrical and thermal transport properties of cubic Sn_0.50Ag_0.25Bi_0.25Se_0.50Te_0.50 thermoelectric materials. X-ray diffraction (XRD) analysis confirmed that the Ge-doped samples exhibited a single cubic phase structure, while scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed a uniform distribution of elements within the samples. The results indicate that increasing the Ge doping content substantially enhances their electrical conductivity, albeit at the expense of elevated thermal conductivity. By optimizing the content of Ge-doping, the thermoelectric figure of merit (ZT) reached 0.74 at 750 K. Notably, while moderate Ge doping enhances electrical transport properties, excessive doping leads to a significant rise in thermal conductivity, ultimately constraining further thermoelectric performance gains. Full article

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12 pages, 3225 KiB

Open AccessArticle

Multiple Slater Determinants and Strong Spin-Fluctuations as Key Ingredients of the Electronic Structure of Electron- and Hole-Doped Pb_10−xCu_x(PO₄)₆O

by Dimitar Pashov, Swagata Acharya, Stephan Lany, Daniel S. Dessau and Mark van Schilfgaarde

Crystals 2025, 15(7), 621; https://doi.org/10.3390/cryst15070621 - 2 Jul 2025

Viewed by 653

Abstract

LK-99, with chemical formula Pb_10−xCu_x(PO₄)₆O, was recently reported to be a room-temperature superconductor. While this claim has met with little support in a flurry of ensuing work, a variety of calculations (mostly based on [...] Read more.

LK-99, with chemical formula Pb_10−xCu_x(PO₄)₆O, was recently reported to be a room-temperature superconductor. While this claim has met with little support in a flurry of ensuing work, a variety of calculations (mostly based on density-functional theory) have demonstrated that the system possesses some unusual characteristics in the electronic structure, in particular flat bands. We have established previously that within DFT, the system is insulating with many characteristics resembling the classic cuprates, provided the structure is not constrained to the P3(143) symmetry nominally assigned to it. Here we describe the basic electronic structure of LK-99 within self-consistent many-body perturbative approach, quasiparticle self-consistent GW (QSGW) approximation and their diagrammatic extensions. QSGW predicts that pristine LK-99 is indeed a Mott/charge transfer insulator, with a bandgap gap in excess of 3 eV, whether or not constrained to the P3(143) symmetry. When Pb₉Cu(PO₄)₆O is hole-doped, the valence bands modify only slightly, and a hole pocket appears. However, two solutions emerge: a high-moment solution with the Cu local moment aligned parallel to neighbors, and a low-moment solution with Cu aligned antiparallel to its environment. In the electron-doped case the conduction band structure changes significantly: states of mostly Pb character merge with the formerly dispersionless Cu d state, and high-spin and low spin solutions once again appear. Thus we conclude that with suitable doping, the ground state of the system is not adequately described by a band picture, and that strong correlations are likely. Irrespective of whether this system class hosts superconductivity or not, the transition of Pb₁₀(PO₄)₆O from being a band insulator to Pb₉Cu(PO₄)₆O, a Mott insulator, and multi-determinantal nature of doped Mott physics make this an extremely interesting case-study for strongly correlated many-body physics. Full article

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18 pages, 15258 KiB

Open AccessArticle

Nanoindentation-Induced Deformation Mechanisms in Sintered Silver: A Multiscale Study Combining Experimental and Molecular Dynamics Simulations

by Yiping Sun, Xinyue Wang, Haixue Chen and Pan Liu

Crystals 2025, 15(7), 620; https://doi.org/10.3390/cryst15070620 - 2 Jul 2025

Viewed by 169

Abstract

Sintered silver, widely used in WBG electronic device packaging for its excellent electrothermal properties and high-temperature stability, faces challenges in macroscopic mechanical behavior and reliability due to porosity, especially for pressureless sintered silver. However, the intrinsic pores inside sintered material introduce uncertainties during [...] Read more.

Sintered silver, widely used in WBG electronic device packaging for its excellent electrothermal properties and high-temperature stability, faces challenges in macroscopic mechanical behavior and reliability due to porosity, especially for pressureless sintered silver. However, the intrinsic pores inside sintered material introduce uncertainties during nanoindentation tests for mechanical characterization. This study investigated the impact of pore distribution on the dislocation behavior of pressureless sintered silver during nanoindentation. Firstly, pressureless sintered silver models with 8–33% porosity were prepared and characterized through scanning electron microscope (SEM) for porosity, electron backscatter diffraction (EBSD) for the geometrically necessary dislocation (GND) density distribution, and transmission electron microscopy (TEM) for the crystal structure and microscopic strain. The EBSD results indicated that nanoindentation caused localized plastic deformation in sintered silver, closely related to its porous structure. The TEM results revealed that sintered silver undergoes dislocation slip during nanoindentation, leading to complex dislocation network formation, while the strain decreased with distance from the indentation. To further investigate the relationship of pore distribution and dislocation behavior during nanoindentation, molecular dynamics (MD) simulations were carried out. The MD results revealed that the dislocation distribution was consistent with the EBSD and TEM results. During loading, with the increased porosity from 10% to 23.7%, the total dislocation length was reduced by 63%, while it led to a 38% increase in total dislocation length with the average pore size decreased from 3.84 nm to 2.88 nm under similar porosity conditions. This study improves the understanding of the deformation mechanisms of porous sintered silver under nanoindentation and provides insight into the mechanical characterization of porous materials. Full article

(This article belongs to the Section Crystal Engineering)

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10 pages, 1898 KiB

Open AccessArticle

Crystal Structure of 4′-Phenyl-1′,4′-Dihydro-2,2′:6′,2″-Terpyridine: An Intermediate from the Synthesis of Phenylterpyridine

by Alexander Sedykh, Maksim Zhernakov, Mariia Becker, Dirk G. Kurth and Klaus Müller-Buschbaum

Crystals 2025, 15(7), 619; https://doi.org/10.3390/cryst15070619 - 1 Jul 2025

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Abstract

The intermediate compound 4′-phenyl-1′,4′-dihydro-2,2′:6′,2″-terpyridine (pdhtpy) was isolated for the first time during the synthesis of 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) and characterised by single-crystal X-ray diffraction. Pdhtpy crystallises in the triclinic crystal system with space group P

\bar{1}

with the following [...] Read more.

The intermediate compound 4′-phenyl-1′,4′-dihydro-2,2′:6′,2″-terpyridine (pdhtpy) was isolated for the first time during the synthesis of 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) and characterised by single-crystal X-ray diffraction. Pdhtpy crystallises in the triclinic crystal system with space group P

\bar{1}

with the following unit cell parameters at 100 K: a = 6.1325(4) Å; b = 8.2667(5) Å; c = 16.052(2) Å; α = 86.829(2)°; β = 82.507(2)°; γ = 84.603(2)°; V = 802.49(9) Å³. The absence of stabilising electron-withdrawing groups renders pdhtpy prone to oxidative conditions. Pdhtpy was obtained as a mixture with ptpy, confirmed by Rietveld refinement of the powder X-ray diffraction pattern. Notably, pdhtpy is the first solid-state 1,4-dihydropyridine lacking electron-withdrawing groups at both positions 3 and 5, distinguishing it from Hantzsch esters and related compounds. Full article

(This article belongs to the Section Organic Crystalline Materials)

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25 pages, 6245 KiB

Open AccessReview

Effect of Interstitial Oxygen on the Microstructure and Mechanical Properties of Titanium Alloys: A Review

by Yaojia Ren, Jiajun Xu, Yingkang Wei, Yingying Liu, Jilei Zhu and Shifeng Liu

Crystals 2025, 15(7), 618; https://doi.org/10.3390/cryst15070618 - 30 Jun 2025

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Abstract

Titanium alloys are of significant value in aerospace, biomedical, and marine engineering applications due to their excellent specific strength and favorable biocompatibility. As a crucial interstitial solute, oxygen significantly influences the mechanical properties of titanium alloys. However, excessive oxygen content can lead to [...] Read more.

Titanium alloys are of significant value in aerospace, biomedical, and marine engineering applications due to their excellent specific strength and favorable biocompatibility. As a crucial interstitial solute, oxygen significantly influences the mechanical properties of titanium alloys. However, excessive oxygen content can lead to severe embrittlement and a significant reduction in ductility. This paper systematically reviews the mechanisms of microstructural evolution induced by oxygen in conventionally manufactured titanium alloys and their impact on mechanical properties, highlighting that conventional processes require complex post-treatments (PT) to achieve a balance between strength and plasticity. This assessment further explores the regulatory mechanisms of oxygen on the microstructure and mechanical properties of laser additive manufactured (LAM) titanium alloys, elucidating the fundamental phenomena regarding the oxygen–microstructure–property relationship. Finally, based on the current research progress, this paper provides an outlook on the future development directions and key research priorities in this field. This review offers valuable insights into the role of oxygen in titanium alloys and the development of high-performance titanium alloys. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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14 pages, 6081 KiB

Open AccessArticle

Investigation on Tensile Behavior of Solid Solution-Strengthened Ni-Co-Cr-Based Superalloy During Long-Term Aging

by Wanqi Hou, Xianjun Guan, Jiaqi Wang, Jinrong Wu, Lanzhang Zhou and Zheng Jia

Crystals 2025, 15(7), 617; https://doi.org/10.3390/cryst15070617 - 30 Jun 2025

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Abstract

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning [...] Read more.

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning grain boundaries and improving strength. Prolonged aging (750 °C, 5000 h) caused M₂₃C₆ to coarsen into brittle chain-like structures (width up to 1.244 μm) and precipitated M₆C carbides, degrading grain boundaries. Aging at 950 °C accelerated this coarsening via LSW kinetics (rate constant: 6.83 × 10⁻² μm³/s), with Mo segregation promoting M₆C formation. Tensile properties resulted from competing γ′ precipitation strengthening (post-aging strength increased up to 23.3%) and grain boundary degradation (elongation dropped from 70.1% to 43.3%). Fracture shifted from purely intergranular (cracks along M₂₃C₆/γ interfaces at 750 °C) to mixed mode (cracks initiated by M₆C fragmentation at 950 °C). These insights support superalloy microstructure optimization and lifetime prediction. Full article

(This article belongs to the Special Issue Crystal Plasticity (4th Edition))

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12 pages, 19537 KiB

Open AccessArticle

Microstructure, Mechanical Properties, Deformation Behavior, and Crystallographic Texture of the Al-Gd-Cr-Ti Quaternary Alloy for Thermal Neutron Absorption

by Sayed M. Amer, Dmitry I. Nikolayev, Tatiana A. Lychagina, Abdelmoneim El-Khouly, Ruslan Yu. Barkov, Alexey S. Prosviryakov, Anastasia V. Mikhaylovskaya, Maria V. Glavatskikh and Andrey V. Pozdniakov

Crystals 2025, 15(7), 616; https://doi.org/10.3390/cryst15070616 - 30 Jun 2025

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Abstract

In this work, we report the identification of a novel quaternary intermetallic phase (Al₂₁GdCrTi) formed during the solidification of a novel Al-Gd-Cr-Ti alloy, which has not been previously documented in the literature to the best of our knowledge. The study also [...] Read more.

In this work, we report the identification of a novel quaternary intermetallic phase (Al₂₁GdCrTi) formed during the solidification of a novel Al-Gd-Cr-Ti alloy, which has not been previously documented in the literature to the best of our knowledge. The study also provides a detailed analysis of microstructure evolution, texture behavior, and the mechanical strengthening effect of rolling processes, along with neutron absorption performance. XRD analysis reveals that the intensity of (022), (113) planes of the as-hot-cold-rolled sample is higher than that of the as-cast due to the change in the direction of some grains in these planes during rolling. The results indicate that the studied alloys scatter neutrons about 100 times less than a nearly pure aluminum alloy. The hardness of the as-cast alloy increased from 36 to 53 HV after cold rolling and to 50 HV after hot rolling-cold rolling. Hot-cold-rolled alloy has a yield strength of 160 MPa and an ultimate tensile strength of 181 MPa, while maintaining an elongation of 11.3%. The studied alloys, containing 4.2 wt.% of the alloying elements 3.8Gd, 0.2Cr, and 0.2Ti (Al-3.8Gd-0.2Cr-0.2Ti), exhibited a yield strength 28 MPa higher than those containing 21 wt.% of the alloying elements 5Cu, 6Gd, and 8Bi (Al-5Cu-6Gd-8Bi). The studied alloys form the basis for the development of high-technology Al-Gd alloys for neutron shielding. Full article

(This article belongs to the Special Issue Development of Light Alloys and Their Applications)

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21 pages, 5673 KiB

Open AccessArticle

Functionalized Magnetic Nanomaterial Based on SiO₂/Ca(OH)₂-Coated Clusters Decorated with Silver Nanoparticles for Dental Applications

by Izabell Crăciunescu, George Marian Ispas, Alexandra Ciorîta and Rodica Paula Turcu

Crystals 2025, 15(7), 615; https://doi.org/10.3390/cryst15070615 - 30 Jun 2025

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Abstract

In this study, an innovative dental functionalized magnetic nanomaterial was developed by incorporating hydrophilic magnetic clusters as an alternative to conventional isolated magnetic nanoparticles, introducing a novel structural and functional concept in dental applications. The ~100 nm magnetic clusters—composed of densely packed 7 [...] Read more.

In this study, an innovative dental functionalized magnetic nanomaterial was developed by incorporating hydrophilic magnetic clusters as an alternative to conventional isolated magnetic nanoparticles, introducing a novel structural and functional concept in dental applications. The ~100 nm magnetic clusters—composed of densely packed 7 nm Fe₃O₄ nanoparticles—were sequentially coated with a silica (SiO₂) layer (3–5 nm) to improve chemical and mechanical stability, followed by an outer calcium hydroxide [Ca(OH)₂] layer to enhance bioactivity and optical integration. This bilayer architecture enables magnetic field-assisted positioning and improved dispersion within dental resin matrices. Silver nanoparticles were incorporated to enhance antimicrobial activity and reduce biofilm formation. The synthesis process was environmentally friendly and scalable. Comprehensive physicochemical characterization confirmed the material’s functional performance. Saturation magnetization decreased progressively with surface functionalization, from 62 to 14 emu/g, while the zeta potential became increasingly negative (from −2.42 to −22.5 mV), supporting its ability to promote apatite nucleation. The thermal conductivity (0.527 W/m·K) closely matched that of human dentin (0.44 W/m·K), and the colorimetric analysis showed improved brightness (ΔL = 5.3) and good color compatibility (ΔE = 11.76). These results indicate that the functionalized magnetic nanomaterial meets essential criteria for restorative use and holds strong potential for future clinical applications. Full article

(This article belongs to the Special Issue Innovations in Magnetic Composites: Synthesis to Application)

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14 pages, 2423 KiB

Open AccessArticle

Properties of Cast Iron Produced with a Limited Share of Pig Iron in the Charge

by Krzysztof Janerka and Jan Jezierski

Crystals 2025, 15(7), 614; https://doi.org/10.3390/cryst15070614 - 30 Jun 2025

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Abstract

The article presents issues related to the melting of cast iron with a limited or zero share of pig iron in the charge. The results of melts conducted in electric induction furnaces are presented. The elimination of pig iron and its replacement with [...] Read more.

The article presents issues related to the melting of cast iron with a limited or zero share of pig iron in the charge. The results of melts conducted in electric induction furnaces are presented. The elimination of pig iron and its replacement with steel or return scrap is highly significant in the context of sustainable production and product life cycle assessment (LCA). The paper presents the results of research carried out during melts conducted under both laboratory and industrial conditions. The chemical composition of the cast iron, its physicochemical properties obtained from the analysis of the cooling curve and its derivative, as well as the structure, were analyzed. It was found that cast iron produced using high-quality steel scrap contains fewer sulfur and phosphorus impurities. However, it was also observed that such cast iron exhibits reduced nucleation ability, which can be improved by applying an inoculation process. Full article

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