Crystals, Volume 13, Issue 8 (August 2023) – 139 articles

Acoustic sensing systems play a critical role in identifying and determining weak sound sources in various fields. In many fault warning and environmental monitoring processes, sound-based sensing techniques are highly valued for their information-rich and non-contact advantages. However, noise signals from the environment reduce the signal-to-noise ratio (SNR) of conventional acoustic sensing systems. Therefore, we proposed novel nonlinear gradient-coiling metamaterials (NGCMs) to sense weak effective signals from complex environments using the strong wave compression effect coupled with the equivalent medium mechanism. Theoretical derivations and finite element simulations of NGCMs were executed to verify the properties of the designed metamaterials. Compared with nonlinear gradient acoustic metamaterials (Nonlinear-GAMs) without coiling structures, NGCMs exhibit far superior performance in terms of acoustic enhancement, and the structures capture lower frequencies and possess a wider angle acoustic response. Additionally, experiments were constructed and conducted using set Gaussian pulse and harmonic acoustic signals as emission sources to simulate real application scenarios. It is unanimously shown that NGCMs have unique advantages and broad application prospects in the application of weak acoustic signal sensing, enhancement and localization. Full article

A polychrome tourmaline crystal from Anjanabonoina pegmatite (Madagascar) was characterized using a multi-analytical approach. The sample showed a complex concentric zoning and a wide range of colors typical of the variety known as “watermelon”. The sample was cut perpendicularly to the c axis. The basal slice exhibits a rim characterized by narrow, differently colored layers parallel to the prism faces and a relatively homogeneous triangular core. Four main pronounced color zones were identified from the rim to core: a dark green rim (M1RVS); a pale green rim (M1RVC); a pale pink rim (M1CR); and a brownish yellow core (M1CG). Compositional variations in the basal slice were studied by scanning electron microscopy and electron microprobe analyses (WDS mode). The Li content was determined via micro-laser-induced breakdown spectroscopy. To deeply characterize the sample, single crystal structure refinement was also performed on fragments extracted from the four zones. The results show that the polychrome tourmaline sample consists of two different species: the three outer zones are Mn-rich fluor-liddicoatite, whereas the inner zone is Mn-rich fluor-elbaite. The structural and compositional characterization of the color zoning shows that each step of the tourmaline growth is related to a change in the geological environment. Full article

The use of silica fume as a partial replacement for Ordinary Portland Cement provides a wide variety of benefits, such as reduced pressure on natural resources, reduced CO₂ footprint, and improved mechanical and durability properties. The formation of more stable crystallographic phases in the hardened cement paste can promote resistance to concrete attacks. However, using coarse silica fume may result in lower expenses and shorter workdays. In this work, coarse silica fume was used as a partial replacement of cement, by weight, at 3%, 5%, and 7%, and it was used as limestone filler at different particle sizes. The size of coarse silica fume used was 238 μm. The microstructural, compositional analysis, and crystalline phase content of mixed cements at different ages were evaluated. The addition of coarse silica fume and limestone promoted pore refinement of the composites and increased the calcium and silica content. The filling effect of fine limestone and coarse silica fume particles, as well as the formation of CSH gel, was found to be the main reason for the densified microstructure. The contributions of combined coarse silica fume and limestone improve the stability of CSH gels and pozzolanic reaction. Full article

The up-conversion (UC) and temperature sensing behaviours of Y₂O₃:Ho³⁺, Yb³⁺ phosphors were investigated. A series of Y₂O₃:Ho³⁺, Yb³⁺ phosphors were synthesized using a solution combustion method. The cubic structure of the Y₂O₃ with an Ia$\overline{3}$ space group was analysed by using X-ray powder diffraction. Scanning electron microscopy was conducted to study the surface morphologies of the UC phosphors. Under 980 nm excitation, the UC emissions of Ho³⁺ from the ⁵S₂ → ⁵I₈, ⁵F₅ → ⁵I₈ and ⁵S₂ → ⁵I₇ transitions were observed, which occurred through UC energy transfer (ET) processes. The Yb³⁺ ion concentration severely affected the UC emission. The sensing behaviour of the phosphor was investigated through the green (⁵F₄, ⁵S₂ → ⁵I₈) to red (⁵F₅ → ⁵I₈) fluorescence intensity ratio (FIR). The maximum absolute and relative sensitivity values of S_A = 0.08 K⁻¹ and S_R = 0.64% K⁻¹ were obtained. The results revealed that the prepared Y₂O₃:Ho³⁺, Yb³⁺ phosphor is suitable for optical sensing at high temperatures. Full article

Generally, the addition of Chromium (Cr) into the dual-phase (DP) steels can suppress bainitic transformation. In this work, the continuous hot-dip galvanization of DP980 steel is thermally simulated with various Cr contents of 0/0.3/0.6 wt.%, and the effect of Cr on bainitic transformation and properties of steels is studied. The results indicate that the bainitic transformation is obviously inhibited. The fraction of bainite decreases with the increasing Cr content. The incubation time is prolonged in the 0.6Cr steel with a slower bainitic transformation rate. Compared to that of 0 and 0.3Cr steels, the 0.6Cr steel exhibits a high tensile strength of 1033 MPa and uniform elongation of 9.1% due to the rapid strain-hardening rate. As a result, the mechanical properties of 0.6Cr steel satisfy the requirements of hot-dip galvanized DP980 steel. Full article

The microstructure and residual stress of polycrystalline diamond compact (PDC) play crucial roles in the performance of PDCs. Currently, in-depth research is still to be desired on the evolution mechanisms of microstructure and residual stress during high pressure high temperature (HPHT) synthesis process of PDCs. This study systematically investigated the influencing mechanisms of polycrystalline diamond (PCD) layer material design, especially the Co content of the PCD layer, on microstructure and residual stress evolution in PDCs via Raman spectroscopy and finite element micromechanical simulation. The research shows that when the original Co content of the PCD layer is higher than 15 wt.%, the extra Co in the PCD layer will migrate backwards towards the carbide substrate and form Co-enrichment regions at the PCD–carbide substrate interface. As the original Co content of the PCD layer increases from 13 to 20 wt.%, the residual compressive stress of diamond phase at the upper surface center of the PCD layer gradually decreases and transforms into tensile stress. When the original Co content of the PCD layer is as high as 30 wt.%, the residual stress transforms back into significant compressive stress again. The microstructure-based micromechanical simulation at the PCD–carbide substrate interface shows that the Co-enrichment region is the key for the transformation of the residual stress of the diamond phase from tensile stress into significant compressive stress. Full article

In this study, trace amounts of In and Ce elements were composite added into a Ag10CuZnSn low-silver brazing filler metal, and the effects of the composite alloying on the solidus and liquidus temperatures, the spreading performance, the microstructure of the filler metal, and the mechanical properties of the joints prepared with these filler metals were studied. The results reveal that the In element can significantly decrease the solidus and the liquidus temperatures of the Ag10CuZnSn alloy, while the Ce element has little effect on the melting temperature. Trace amounts of In and Ce elements can obviously increase the spreading areas of the filler metals on the pure Cu and 304 stainless steel base metals. The In and Ce elements can refine the microstructure of the filler metals. When the contents of In and Ce are 1.5 wt% and 0.15 wt%, respectively, the microstructure refinement effect is the most obvious, and the shear strength of the 304 stainless steel brazed joint also achieves a maximum value of 375 MPa. Excessive addition of In and Ce can form brittle intermetallic compounds in the filler metal, decreasing the brazed joints' shear strength. Full article

One of the main challenges is using an effective photocatalyst that responds to a broad range of visible light for hydrogen production during water splitting. Series types of photocatalysts based on magnetic ferrite nanostructure were fabricated via a two-step co-precipitation technique. Precisely, four types of magnetic structures: magnetite nanoparticles (MNPs), zinc cobalt ferrite nanoparticles (ZCFNPs), hybrid magnetite/zinc cobalt ferrite nanoparticles (MNPs @ ZCFNPs), and hybrid zinc cobalt ferrite/magnetite nanoparticles (ZCFNPs @ MNPs) were used to fabricate magnetic photocatalysts. The characterizations of the fabricated magnetic photocatalysts were investigated via TEM, zeta potential, XRD, VSM, and UV–VIS spectroscopy. ZCFNPs @ MNPs showed the smallest particle with size ≈11 nm. The magnetization value of ZCFNPs @ MNPs (59.3 emu/g) was improved compared to the MNPs (41.93 emu/g). The produced hydrogen levels via photocatalyst were 60, 10, 24, and 1.4 mmole min⁻¹ g⁻¹ for MNPs, ZCFNPs, MNPs @ ZCFNPs, and ZCFNPs @ MNPs, respectively, under visible light with magnetic force. MNPs displayed outstanding performance as magnetic photocatalysts for the water-splitting process. Full article

In this article, we present the procedure of preparation of flexible electronic paper with a photosensitive azo dye layer as the key element for changing the orientation of the polarization plane. The main steps of the technology for the fabrication of flexible e-paper are reported. The possible production of Digital Mirror Devices and the roll-to-roll process is discussed. Images on flexible e-paper are demonstrated, including bank card options. The advantages of optically rewritable e-paper technology in comparison with the e-ink usually used for this purpose are highlighted. Potential applications of flexible optically rewritable e-paper include price tags for supermarkets, indoor and outdoor advertisements, smart card labels, etc. Full article

In the correspondence, a novel polished-D-shape photonic crystal fiber sensor structure on the basis of surface plasmon resonance is proposed for measuring analyte refractive index. With the help of the finite element method, sensing performances of the structure have been analyzed through numerical simulations along with a step-by-step optimization. In this design, different capillaries are gathered and processed to form a D-shape silica structure and nano-scale gold material is coated on the flattened surface. With utilization of a thin gold film and solid silica background, the resonance effect is excited and the loss curve has red shift along with an increase in refractive index, which is applied for sensing. From the simulation and calculation results, the final sensor structure achieves the optimal performance where values of maximum and average sensitivity reach 32,000 and 12,167 nm/RIU along with a sensing coverage of refractive index from 1.26 to 1.32. Also, the proposed design obtains a range of resonant wavelength from 1810 to 2540 nm. We believe the proposed sensor can be a potential candidate for organic and biological detection and related applications. Full article

The crystal structures of red and blue-black tin(II) oxide, SnO, have been determined for the first time by single-crystal X-ray diffraction. Blue-black SnO crystallizes in the tetragonal space group P4/nmm, representing a layer structure consisting of the square–pyramidally coordinated tin and slightly distorted tetrahedrally coordinated oxygen atoms, in accordance with previous results. In contrast, red SnO crystallizes in the orthorhombic centrosymmetric space group Pbca rather than in the non-centrosymmetric space group Cmc2₁, as assumed for a long time. Its layer structure consists of very regular, trigonal–pyramidally coordinated tin atoms as well as trigonal–planar coordinated oxygen atoms. Special care was taken on space group determination, including lattice centering. C-centering could be excluded because of systematic absence violations detected when collecting and processing a primitive triclinic dataset and by generating precession images. In the absence of meaningful extinction conditions resulting from the very small crystal under examination, the structure was initially solved and refined in the triclinic space group P1. Subsequently, the observed atom coordinates were used to reconstruct the actual symmetry skeleton. The various possibilities to identify the correct space group starting from the triclinic solution are demonstrated, and the unique structural features of the crystal structure are visualized. Full article

Tissue engineering (TE) and nanomedicine require devices with hydrophilic surfaces to better interact with the biological environment. This work presents a study on the wettability of cubic silicon-carbide-based (SiC) surfaces. We developed four cubic silicon-carbide-based epitaxial layers and three nanowire (NW) substrates. Sample morphologies were analyzed, and their wettabilities were quantified before and after a hydrogen plasma treatment to remove impurities due to growth residues and enhance hydrophilicity. Moreover, sample biocompatibility has been assessed with regard to L929 cells. Our results showed that core–shell nanowires (SiO₂/SiC NWs), with and without hydrogen plasma treatment, are the most suitable candidate material for biological applications due to their high wettability that is not influenced by specific treatments. Biological tests underlined the non-toxicity of the developed biomaterials with regard to murine fibroblasts, and the proliferation assay highlighted the efficacy of all the surfaces with regard to murine osteoblasts. In conclusion, SiO₂/SiC NWs offer a suitable substrate to develop platforms and membranes useful for biomedical applications in tissue engineering due to their peculiar characteristics. Full article

This article mainly studies the improvement of the properties of the 1Cr18Ni9Ti material after laser shock peening. The 1Cr18Ni9Ti material is the main material used to make aviation ducts, and improving the fatigue life of aviation ducts can significantly improve the safety performance of aviation engines. The article combines simulation and experiment to study the improvement effect of laser shock peening on the material’s properties. The main results are as follows: The fatigue test showed that, under the same stress load, laser shock peening can greatly extend the fatigue life of the specimen, with the 3J process having the best effect. EBSD analysis showed that the 3J process has the best grain refinement effect. The X-ray diffraction method proved that the measurement results of residual compressive stress under the 3J process are optimal. Overall, it is shown that the properties of the 1Cr18Ni9Ti material can be greatly improved under the 3J process. Full article

The insulator-to-metal transition upon the thermal reduction of perovskites is a well-known yet not completely understood phenomenon. By combining different surface-sensitive analysis techniques, we analyze the electronic transport properties, electronic structure, and chemical composition during the annealing and cooling of high-quality BaTiO₃ single crystals under ultra-high-vacuum conditions. Our results reveal that dislocations in the surface layer of the crystal play a decisive role as they serve as easy reduction sites. In this way, conducting filaments evolve and allow for turning a macroscopic crystal into a state of metallic conductivity upon reduction, although only an extremely small amount of oxygen is released. After annealing at high temperatures, a valence change of the Ti ions in the surface layer occurs, which becomes pronounced upon the quenching of the crystal. This shows that the reduction-induced insulator-to-metal transition is a highly dynamic non-equilibrium process in which resegregation effects in the surface layer take place. Upon cooling to the ferroelectric phase, the metallicity can be preserved, creating a “ferroelectric metal.” Through a nanoscale analysis of the local conductivity and piezoelectricity, we submit that this phenomenon is not a bulk effect but originates from the simultaneous existence of dislocation-based metallic filaments and piezoelectrically active areas, which are spatially separated. Full article

Low fracture toughness has been a major barrier for the structural applications of cast Mg-Gd-Y-Zr alloys. In this work, the tensile properties and fracture toughness of a direct-chill-cast Mg-9Gd-4Y-0.5Zr (VW94K) alloy were investigated in different conditions, including its as-cast and as-homogenized states. The results show that the tensile properties of the as-cast VW94K alloy are greatly improved after the homogenization treatment due to the strengthening of the solid solution. The plane strain fracture toughness values K_Ic of the as-cast and as-homogenized VW94K alloys are 10.6 ± 0.5 and 13.8 ± 0.6 MPa·m^1/2, respectively, i.e., an improvement of 30.2% in K_Ic is achieved via the dissolution of the Mg₂₄(Gd, Y)₅ eutectic phases. The initiation and propagation of microcracks in an interrupted fracture test are observed via an optical microscope (OM) and scanning electron microscope (SEM). The fracture surfaces of the failed samples after the fracture toughness tests are examined via an SEM. The electron backscatter diffraction (EBSD) technique is adopted to determine the failure mechanism. The results show that the microcracks are initiated and propagated across the Mg₂₄(Gd, Y)₅ eutectic compounds in the as-cast VW94K alloy. The propagation of the main cracks exhibits an intergranular fracture pattern and the whole crack propagation path displays a zigzag style. The microcracks in the as-homogenized alloy are initiated and propagated along the basal plane of the grains. The main crack in the as-homogenized alloy shows a more tortuous fracture characteristic and a trans-granular crack propagation behavior, leading to the improvement of the fracture toughness. Full article

This study is devoted to the morphological/dynamic instability analysis of directional crystallization processes in finite domains with allowance for melt convection. At first, a linear instability theory for steady-state crystallization with a planar solid/liquid interface in the presence of convection was developed. We derived and analyzed a dispersion relation showing the existence of morphological instability over a wide range of wavenumbers. This instability results from perturbations arriving at the solid/liquid interface from the cooled wall through the solid phase. Also, we showed that a planar solid/liquid interface can be unstable when it comes to dynamic perturbations with a zero wavenumber (perturbations in its steady-state velocity). A branch of stable solutions for dynamic perturbations is available too. The crystallizing system can choose one of these branches (unstable or stable) depending of the action of convection. The result of morphological and dynamic instabilities is the appearance of a two-phase (mushy) layer ahead of the planar solid/liquid interface. Therefore, our next step was to analyze the dynamic instability of steady-state crystallization with a mushy layer, which was replaced by a discontinuity interface between the purely solid and liquid phases. This analysis showed the existence of dynamic instability over a wide range of crystallization velocities. This instability appears in the solid material at the cooled wall and propagates to the discontinuity interface, mimicking the properties of a mushy layer. As this takes place, at a certain crystallization velocity, a bifurcation of solutions occurs, leading to the existence of unstable and stable crystallization branches simultaneously. In this case, the system chooses one of them depending of the effect of the convection as before. In general, the crystallizing system may be morphologically/dynamically unstable when it comes to small perturbations arriving at the phase interface due to fluctuations in the heat and mass exchange equipment (e.g., fluctuations in the freezer temperature). Full article

Monolayer MoS₂ has emerged as a highly promising candidate for next-generation electronics. However, the production of monolayer MoS₂ with a high yield and low cost remains a challenge that impedes its practical application. Here, a significant breakthrough in the batch production of wafer-scale monolayer MoS₂ via chemical vapor deposition is reported. Notably, a single preparation process enables the growth of multiple wafers simultaneously. The homogeneity and cleanliness of the entire wafer, as well as the consistency of different wafers within a batch, are demonstrated via morphology characterizations and spectroscopic measurements. Field-effect transistors fabricated using the grown MoS₂ exhibit excellent electrical performances, confirming the high quality of the films obtained via this novel batch production method. Additionally, we successfully demonstrate the batch production of wafer-scale oxygen-doped MoS₂ films via in situ oxygen doping. This work establishes a pathway towards mass preparation of two-dimensional materials and accelerates their development for diverse applications. Full article

Aspartate semialdehyde dehydrogenase (ASADH) catalyzes the biosynthesis of several essential amino acids, including lysine, methionine, and threonine, and bacterial cell components. Thus, ASADH is a crucial target for developing new antimicrobial agents that can potentially disrupt the biosynthesis of essential amino acids, thereby inhibiting the growth of pathogens. Herein, the crystal structures of ASADH obtained from Porphyromonas gingivalis (PgASADH, UniProtKB code A0A1R4DY25) were determined in apo- and adenosine-2′-5′-diphosphate (2′,5′-ADP)-bound complex forms at a resolution of 1.73 Å. The apo- and 2′,5′-ADP-complexed crystals of PgASADH belonged to the space groups of I2₁2₁2₁ and C222₁, respectively. Analytical size-exclusion chromatography showed a stable PgASADH dimer in a solution. Clustering analysis and structural comparison studies performed on PgASADH and previously known ASADHs revealed that ASADHs, including PgASADH, can be classified into three types depending on sequential and structural differences at the α-helical subdomain region. These findings provide valuable insights into developing structure-based species-specific new antibacterial drugs against the oral pathogen P. gingivalis. Full article

High-quality single crystals with empirical composition Y₂.₉₆Sm₀.₀₄Ga₅O₁₂ (YGG: Sm³⁺) were successfully prepared by the optical floating zone method for the first time and compared with related single crystals of Y₂.₉₆Sm₀.₀₄Al₅O₁₂ (YAG: Sm³⁺). With both crystals, XRD showed that Sm³⁺ entered the cubic-phase structure. Optical absorption spectra produced a series of peaks from Sm³⁺ in the 250 nm to 550 nm range, and photoluminescence excitation (PLE) spectra detected at 613 nm showed strong excitation peaks at 407 nm and 468 nm. A strong emission peak at 611 nm (orange-red light) was observed in the photoluminescence (PL) spectra under excitations at both 407 and 468 nm, respectively, but it was much brighter under excitation at 407 nm. Furthermore, with both emission spectra, the peaks from the YGG: Sm³⁺ crystal were significantly more intense than those from the YAG: Sm³⁺ crystal, and both experienced a blue shift. In addition, under excitation at 407 nm, the color purity of the emitted orange-red light of YGG: Sm³⁺ was higher than that of the YAG: Sm³⁺ crystal, and the fluorescence lifetime for the ⁴G_5/2 → ⁶H_7/2 transition of YGG: Sm³⁺ was longer than that of the YAG: Sm³⁺ crystal. The optical properties of the YGG: Sm³⁺ crystal are better than those of the YAG: Sm³⁺ crystal. Full article

We present the results of a twofold experimental and computational study of (0001) GaN/AlN multilayers forming pseudomorphic superlattices. High-Resolution Transmission Electron Microscopy (HRTEM) shows that heterostructures with four c-lattice parameters thick GaN Quantum Wells (QW) are misfit-dislocation free. Accurate structural data are extracted from HRTEM images via a new methodology optimizing the residual elastic energy stored in the samples. Total energy calculations are performed with several models analogous to the experimental QWs with increasing thicknesses of GaN, whereas this of the AlN barrier is kept fixed at n = 8 c-lattice parameters. With vanishing external stresses, minimum energy configurations of the studied systems correspond to different strain states. Linear elasticity accurately yields the corresponding lattice parameters, suppressing the need for on-purpose total energy calculations. Theoretically justified parabolic fits of the excess interfacial energy yield the values of interfacial stress and elastic stiffness as functions of the GaN QW thickness. Total species-projected densities of states and gap values extracted from there allow deciphering the effect of the evolving strain on the electronic structure of the superlattice. It is found that the gap energy decreases linearly with increasing the strain of the QW. These results are briefly discussed in the light shed by previous works from the literature. Full article

The research on molybdenum disulphide (MoS${}_2$) has progressed remarkably in the last decade, prompted by the increasing interest for this material as a potential candidate in future ultrathin optoelectronic devices. MoS${}_2$ is a layered semiconductor with a gap in the visible region, which can be exfoliated down to the mono-layer form. Since the discovery of the exceptional optoelectronic properties of 2D MoS${}_2$, Raman spectroscopy has been extensively used as a tool to characterize the structure and thickness of MoS${}_2$ films. Recent works on MoS${}_2$-metal interfaces have shown that Raman spectra are significantly affected by the interaction with metals. However, a complete understanding of how such interaction modifies the MoS${}_2$ vibrational properties is still lacking. Studying this subject with both experimental and theoretical methods will provide fundamental insight into the interface physics of MoS${}_2$-metal systems, which is crucial for the fabrication of metal contacts and for the development of metal-assisted synthesis methods. This review summarizes the main results concerning Raman spectroscopy studies of heterosystems between MoS${}_2$ and transition metals, providing both a basis and directions for future research. Full article

In this paper, we present concurrent atomistic-continuum (CAC) simulations of the hydrogen (H) diffusion along a grain boundary (GB), nearby which a large population of dislocations are piled up, in a plastically deformed bi-crystalline bcc iron sample. With the microscale dislocation slip and the atomic structure evolution at the GB being simultaneously retained, our main findings are: (i) the accumulation of tens of dislocations near the H-charged GB can induce a local internal stress as high as 3 GPa; (ii) the more dislocations piled up at the GB, the slower the H diffusion ahead of the slip–GB intersection; and (iii) H atoms diffuse fast behind the pileup tip, get trapped within the GB, and diffuse slowly ahead of the pileup tip. The CAC simulation-predicted local H diffusivity, $D_{\mathrm{pileup}-\mathrm{tip}}$, and local stresses, $\sigma$, are correlated with each other. We then consolidate such correlations into a mechanics model by considering the dislocation pileup as an Eshelby inclusion. These findings will provide researchers with opportunities to: (a) characterize the interplay between plasticity, H diffusion, and crack initiation underlying H-induced cracking (HIC); (b) develop mechanism-based constitutive rules to be used in diffusion–plasticity coupling models for understanding the interplay between mechanical and mass transport in materials at the continuum level; and (c) connect the atomistic deformation physics of polycrystalline materials with their performance in aqueous environments, which is currently difficult to achieve in experiments. Full article

In the present study, we extensively explored the high-pressure behaviors and vibrational properties of amblygonite LiAlPO₄F with elevated pressures up to 34.3 GPa based on single-crystal X-ray diffraction measurements, Raman spectroscopy, and DFT calculations. The compressibility and elastic properties of amblygonite were determined first. Specifically, the obtained isothermal bulk modulus of LiAlPO₄F is 128(4) GPa and the triclinic phase exhibited anisotropic compression with axial compressibility β_c > β_a > β_b with a ratio of 1.11:1.00:1.20. The Raman spectra showed no indication of phase transformation and were used to obtained mode Grüneisen parameters. The average Grüneisen parameter for PO₄ tetrahedral sites was smaller than for the LiO₄F sites. Our results provide new insights into the phase stability and elastic properties of lithium-fluorite granites at extreme conditions. Full article

Covalent organic framework (COF)-supported palladium catalysts have garnered enormous attention for cross-coupling reactions. However, the limited linkage types in COF hosts and their suboptimal catalytic performance have hindered their widespread implementation. Herein, we present the first study immobilizing palladium acetate onto a dioxin-linked COF (Pd/COF-318) through a facile solution impregnation approach. By virtue of its permanent porosity, accessible Pd sites arranged in periodic skeletons, and framework robustness, the resultant Pd/COF-318 exhibits exceptionally high activity and broad substrate scope for the Suzuki–Miyaura coupling reaction between aryl bromides and arylboronic acids at room temperature within an hour, rendering it among the most effective Pd/COF catalysts for Suzuki–Miyaura coupling reactions to date. Moreover, Pd/COF-318 demonstrates excellent recyclability, retaining high activity over five cycles without significant deactivation. The leaching test confirms the heterogeneity of the catalyst. This work uncovers the vast potential of dioxin-linked COFs as catalyst supports for highly active, selective, and durable organometallic catalysis. Full article

The increase of device lifetime and reliability of THz photomixers will play an essential role in their possible future application. Therefore, their optimal work conditions/operation range, i.e., the maximal incident optical power should be experimentally estimated. We fabricated and tested THz photomixer devices based on nitrogen-implanted GaAs integrated with a Bragg reflector. Raman spectroscopy was applied to investigate the material properties and to disclose any reversible or irreversible material changes. The results indicate that degradation effects in the photomixer structures/material could be avoided if the total optical power density does not exceed levels of about 0.7 mW/µm² for 100 min of operation. Furthermore, the investigations performed during 1000 min of optical exposure on the photomixer devices’ central region comprising interdigitated metal-semiconductor-metal (MSM) structures suggest a reversible “curing” mechanism if the power density level of ~0.58 mW/µm² is not exceeded. Long-term operation (up to 1000 h) reveals that the photomixer structures can withstand an average optical power density of up to ~0.4 mW/µm² without degradation when biased at 10 V. Besides the decrease of the position of the A_1g (LO) Raman mode from ~291 cm⁻¹ down to ~288 cm⁻¹ with increasing optical power density and operation time, broad Raman modes evolve at about 210 cm⁻¹, which can be attributed to degradation effects in the active photomixer/MSM area. In addition, the performed carrier lifetime and photomixer experiments demonstrated that these structures generated continuous wave sub-THz radiation efficiently as long as their optimal work conditions/operation range were within the limits established by our Raman studies. Full article

The preparations and structural characteristics of three-dimensional Zn(II) metal-organic frameworks (MOFs) with dipyridyl-olefin and tricarboxylate are reported. The solvothermal reactions of zinc(II) nitrate hexahydrate, 1,4-bis [2-(4-pyridyl)ethenyl]benzene (bpeb), and 4,4′,4″,-benzene-1,3,5-triyl-tris(benzoic acid) (H₃btb) furnished three Zn(II) MOFs (1–3) with new topologies. Depending on the temperature or mole-ratio variations, self-interpenetrated [Zn₂(bpeb)(btb)(OH)]·DMF·H₂O (1), noninterpenetrated [Zn₃(btb)₂(bpeb)]·xSolvent (2), and fourfold interpenetrated [Zn₂(Hbtb)₂(bpeb)][Zn₂(Hbtb)₂(bpeb)][Zn₄(Hbtb)₄(bpeb)₂] (3) structures were generated with different molecular building blocks. It is interesting that although all three MOFs contain the same metal cation, anion, and spacer ligand, they show different emissions due to structure and connectivity. Full article

The engineering of new states of matter through Floquet driving has revolutionized the field of condensed matter physics. This technique enables the creation of hybrid topological states and ordered phases that are absent in normal systems. Crystalline structures, exemplifying spatially ordered systems under periodic driving, have been extensively studied. However, recent focus has shifted towards discrete time crystals (DTCs), periodically driven quantum many-body systems that break time translation symmetry under specific conditions. In this paper, the model of discrete time crystals is extended to allow for the formation of time-varying tesseracts, allowing for the investigation of time translational symmetry in pseudo-higher-dimensional lattice systems. Full article

The process of biomineralization of apatite in nature has been studied by scientists from various fields of science for more than a century. Unlike the volcanogenic, hydrothermal, and other types of igneous apatites, the genesis of which is entirely clear, the formation of phosphate ores of marine sedimentary origin is still debatable. Since phosphate concentrations in water bodies are too low for the spontaneous precipitation of solid phosphates, the study of different ways for their concentration is of particular interest. In this work, phase equilibria in the system CaO–P₂O₅–HF–H₂O at 298 K, involving fluorapatite formation, have been studied. Fluorapatite is known to be the most common phosphate mineral and the main source of phosphorus on Earth, playing an important role in the mineralization process of dental tissues in vertebrates. The equilibrium in the system defined above was studied at a low mass fraction of the liquid phase components, i.e., in conditions close to natural. It has been shown that the compounds of variable composition with the fluorapatite structure containing HPO₄²⁻ ions were formed in the acid region of this system. These compounds are formed at pH ≤ 7.0 and have invariant points with monetite, CaHPO₄, and fluorite, CaF₂. Stoichiometric fluorapatite was formed at the lowest concentrations of the liquid phase components in a neutral and weakly alkaline medium and had an invariant point with Ca(OH)₂. The composition of the resulting equilibrium solid phases was found to be dependent on the Ca/P ratio of the initial components and pH of the equilibrium liquid phase. Fluorite CaF₂ was present in each sample obtained in this study. Full article

The pressure–temperature scales in DAC and shock wave (SW) experiments should be corrected by taking into account the thermal pressure shifts. In the present contribution, it is further claimed that first-principle ab initio DFT and MD simulations should serve as an anchor for correcting the pressures and temperatures reported by DAC and SW experiments. It was concluded that upon deriving the actual pressure sensed by the explored sample, the thermal pressure and the temperature shifts must be taken into account when constructing melting curves. Therefore, melting curves measured by diamond anvil cells for 3d elements do not contribute to a better understanding of the geophysical Earth’s inner core. In addition, the advantage of the Lindemann–Gilvarry vs. Simon–Glatzel fitting procedure of melting curves is shown. Full article

In this study, we investigate how changing the nitrogen flow rate, the length of time during deposition, and the intensity of pressure have an impact on the resulting chromium oxynitride coatings. Depending on the sputtering conditions, the X-ray diffraction analyses reveal different textures in the Cr₂O₃ and Cr₂N phases. Films deposited with varying nitrogen flow rates and deposition durations experience compressive strains, whereas films produced with varying sputtering pressures witness tensile stresses. Film surface energies and contact angles were measured with a contact angle goniometer. Because of their hydrophobic properties, chromium oxynitride coatings may find use as water-repellent, self-cleaning surfaces. Chromium oxynitride films’ absorption and transmission curves were recorded using a UV-Vis-NIR spectrophotometer. The band gap of chromium oxynitride coatings reduces with a rise in the flow of nitrogen and sputtering time but widens with increasing deposition pressure. Full article