Crystals, Volume 12, Issue 12 (December 2022) – 167 articles

In this study, SHS was used to produce metal-intermetallic-ceramic laminate AlMg6-NiAl-TiC composite. The experiment conducted without a cylindrical powder pellet holder produced no joint between the NiAl and AlMg6 sheet. On the other hand, the experiment conducted inside a cylindrical powder pellet holder (CPPH) with a blind hole produced a joint. It was found that the AlMg6 sheet had a temperature of 400–550 °C across its entire thickness during SHS. The study of the microstructure and energy-dispersive analysis (EDS) of AlMg6-NiAl-TiC composite showed that it had five layers: (1) ceramic layer of 7-mm-thick TiC; (2) the upper diffusion layer that formed at the interface between NiAl and TiC consisted of TiC + NiAl; (3) an intermetallic layer, which consisted of 13-mm-thick NiAl; (4) the lower diffusion layer, which formed at the interface between NiAl and AlMg6; and (5) a layer of 4-mm-thick aluminum alloy AlMg6. The EDS showed that during the synthesis of NiAl and its interaction with the surface of the AlMg6 sheet, mixing of the components of the initial materials (NiAl, AlMg6) in the joint interface occurs. At the interface of NiAl and AlMg6, the microhardness was 790–870 HV, which indicates the presence of quenching structures in the melted zones. Full article

The presence of porosity within magnesium-based orthopaedic implants is known to be beneficial, promoting cell proliferation and vascularisation. However, the presence of porosity increases the surface area available for corrosion, compounding the issue of high corrosion rates which has long been plaguing magnesium-based materials. This work looks at the influence of hydroxyapatite and phosphate conversion coatings on the corrosion performance of conventionally cast, dense Mg-Zn-Zr alloys and binder jet additive manufactured porous Mg-Zn-Zr scaffolds. The performance of coating on dense Mg-Zn-Zr was found to be more effective than the coating on the porous Mg-Zn-Zr scaffold, with the discrepancies attributed to both the microstructure and geometric influence of the binder jet additive manufactured, porous Mg-Zn-Zr scaffold, which not only increases the rate of hydrogen evolution but also reduces the ability of the hydrogen gas generated within the pore channels to escape to the sample’s surface. This restricts the effectiveness of coating application for porous Mg scaffold. Furthermore, the limited diffusion within the pore channels can also result in differing localized corrosion environments, causing discrepancies between the localised corrosion environment within the pore channels and that at the bulk electrolyte. Full article

The effect of the secondary α phase on stress corrosion cracking of a novel metastable β titanium alloy, Ti-6Mo-5V-3Al-2Fe, in 3.5% NaCl solution was investigated by slow strain rate testing. Fine acicular secondary α phase was obtained by aging at the low temperature of 520 °C, and coarsened rod-like secondary α phase was obtained by aging at the high temperature of 680 °C. The electrochemical measurement results and slow strain rate testing results show that the microstructure contained with fine acicular secondary α phase exhibits better corrosion resistance and less stress corrosion cracking susceptibility. The fracture morphology exhibits a mixed fracture characteristic with shallow and small dimples, as well as tear ridges and flat facets with undulating surfaces. The combination of Absorption Induced Dislocation Emission and Hydrogen Enhanced Localized Plasticity is the main mechanism for stress corrosion cracking. Fine acicular secondary α phase with narrow spacing leads to less accumulated dislocations and smaller localized stress, so that has a beneficial effect on stress corrosion performance. Full article

In this work the n-GaN(1000) surface is used as a source of nitrogen atoms in order to obtain niobium nitride film by a surface-mediated nitridation technique. To this end, the physical vapor deposition of the niobium film on GaN is followed by sample annealing at 1123 K. A thermally induced decomposition of GaN and interfacial mixing phenomena lead to the formation of a niobium nitride compound, which contains Nb from thin film and N atoms from the substrate. The processes allowed the obtaining of ordered NbN_x films on GaN. Structural and chemical properties of both the GaN substrate and NbN_x films were studied in-situ by surface-sensitive techniques, i.e., X-ray and UV photoelectron spectroscopies (XPS/UPS) and a low-energy electron diffraction (LEED). Then, the NbN_x/GaN surface morphology was investigated ex-situ by scanning tunneling microscopy (STM). Full article

In this paper, we reported changes in the growth morphology of n+InAs nanowires (NWs) doped with Te which were selectively grown on nano-hole patterned InP(111)B substrates using an MOCVD method. While the vertical growth of InAs NWs in the <111> direction was extremely suppressed, their lateral growth was enhanced when the diethyl-tellurium (DETe) flow rate was increased as they grew. Moreover, the sidewall planes evolved from ($1\overline{1}0$) (90° against the (111) plane) to a reverse-tapered morphology, which had a 62° slope against the InP (111)B plane, when the Te flow rate and growth time were increased. This indicates that the surfactant effect of adsorbed Te atoms on InAs changes the relative growth rate between (111) and ($1\overline{1}0$) due to the increase in surface free energy in the growth plane. Full article

In small-scale continuous crystallization, particle suspension and residence time distribution are critical factors determining operability and product quality. Here, the Taylor–Couette crystallizer stands out for its high flexibility. Its characteristic vortex structure intensifies local mixing, thus improving the suspension and simultaneously narrowing the residence time distribution, whereby these effects can be adjusted by operating and design parameters. However, the operating window is limited by the prerequisite of sufficient particle suspension. In this study, we investigated the suspension behavior and its impact on the attainable liquid phase residence time distribution and the flow regimes observed. For this purpose, the just-suspended rotation rate was visually determined for different design and operating parameters. A correlation was regressed from experimental data, showing that this rotation rate was mainly affected by the radius ratio of the rotor and stator. In addition, the liquid phase residence time distribution was measured by tracer experiments in regions of sufficient suspension, validating a correlation from the literature. With a combination of both correlations, the design parameters of the apparatus can thus be optimized according to the goal of, for example, a narrow residence time distribution in the suspended state. Full article

Additive manufacturing (AM) can quickly and easily obtain lattice structures with light weight and excellent mechanical properties. Body-centered cubic (BCC) lattice structure is a basic type of lattice structure. BCC with Z strut (BCCZ) lattice structure is a derivative structure of BCC lattice structure, and it has good adaptability to AM. Generally, the thickness of each pillar in the BCCZ lattice structure is uniform, which results in the uneven stress distribution of each pillar. This makes the potential of light weight and high strength of the BCCZ lattice structure not fully played, and the utilization rate of materials can be further improved. This paper designs an optimization method. Through the structural analysis of a BCCZ lattice structure, an optimization method of a BCCZ lattice structure based on parametric modeling parameters is presented. The section radius of all pillars in the BCCZ lattice is taken as a design variable, and the specific sensitivity analysis method and simulated full stress optimization idea are successively used to determine the optimal section radius of each pillar. Finally, the corresponding model is designed and samples are manufactured by LPBF technology for simulation and experimental verification. The results of simulation and experiment show that the strength limit of the optimized parts increased by 18.77% and 18.43%, respectively, compared with that before optimization. Full article

In the present review the focus is set on filled antimony-based skutterudites as they are among the most promising TE materials. Thermoelectric properties (at 300 K and 800 K) of more than 1200 compositions from more than 250 publications from 1996 to 2022 were collected and evaluated. In various figures the dependence of the peak ZT for single-filled, double-filled and multi-filled compounds of p- and n-type skutterudites on the publishing year, the peak temperature, electrical resistivity, thermal and lattice thermal conductivity, the power factor and the fillers are displayed. Together with plots of electrical resistivity versus Seebeck coefficient and especially thermal conductivity versus power factor these evaluations etc. may help to find the ideal skutterudite material for practical applications. Full article

Objective: Two kinds of fire-resistant steel with different Nb content (Nb-free and 0.03 wt.%) were prepared for studying the effects of Nb addition on the elevated-temperature strength of fire-resistant steel. Methods: Two stages of heat treatment were carried out on the steels to obtain different microstructures. Typical microstructures, dislocation, and precipitates morphology of steels were observed by SEM and TEM. The dislocation density was calculated by the X-ray data from the microstructures. High temperature and room temperature mechanical properties of steels were determined by tensile testing. Results: The results showed that the YS of N2-HR steel (addition of 0.03 wt.% Nb) at RT and 600 °C was higher than N1-HR steel (Nb-free) by about 81 and 30 MPa, respectively. This indicates that Nb is an alloying element as effective as Mo in increasing the elevated-temperature strength of fire-resistant steel. The dominant strengthening mechanisms of Nb addition on elevated-temperature yield strength are precipitation strengthening and bainite strengthening. Conclusions: Theoretical analysis shows that there are two precipitation strengthening stages in fire-resistant steel: (1) increasing dislocation density during hot rolling, and (2) blocking dislocation movement and recovery in tensile testing. The results also show that the effect of fine grain strengthening is not obvious at high temperature, but is obvious at room temperature. Full article

Dental caries is a progressive disease with varying phases of demineralization and remineralization, and the scope of reversing the carious lesion is increased if it is diagnosed before there is surface cavitation. Preventive management strategies are directed towards making the enamel more resistant towards acid dissolution. The caries preventive protocol has always been fluoride-centric. Repeated application of fluoride gives rise to acquired fluoride resistance strains of Streptococci mutans which can be transient or permanent. The need of the hour is an effective remineralizing protocol which is one which brings about a change in enamel crystal and makes it more resistant to the acidic challenges of the oral cavity. The authors have devised a protocol in which irradiation with aluminum gallium arsenide crystals LASER can bring about a sanative change in crystal and lead to greater acid resistance of the enamel crystal and thus potentiate the remineralization of non-cavitated lesions. The concept of aluminum gallium arsenide–assisted caries inhibition and the proposed hypothesis of the mechanism of action is discussed. Full article

Tl[CB₁₁H₁₂] was prepared with a reaction of Tl₂[CO₃] with the acid of the monocarba-closo-dodecaborate anion (H₃O)[CB₁₁H₁₂] in aqueous solution as prismatic colorless single crystals by isothermal evaporation from the clear brine. It crystallizes in a monoclinic primitive structure with the space group P2₁/c (a = 685.64(3) pm, b = 1978.21(9) pm, c = 1006.89(5) pm, β = 132.918(3)° for Z = 4), which can be derived from the halite-type arrangement if the closo-carbaborate cages are considered as spheres. Due to the different atoms in the [CB₁₁H₁₂]⁻ anion, Tl[CB₁₁H₁₂] features interesting C–H^δ+ ∙∙∙ ^δ−H–B interactions near to non-classical hydrogen bridges (“dihydrogen bonds”) and exhibits considerably different luminescence properties compared to regular closo-hydroborates, such as Tl₂[B₁₀H₁₀], Tl₂[B₁₂H₁₂] and Tl₃Cl[B₁₂H₁₂]. Tl[CB₁₁H₁₂] shows strong photoluminescence (PL) at 390 nm, while the excitation bands for this broad band are located at 245 and 280 nm. It is caused by an interconfigurational [Xe]4f¹⁴5d¹⁰6s² (³P₁) to [Xe]4f¹⁴5d¹⁰6s¹6p¹ (¹S₀) transition, which is also known as lone-pair luminescence. The quantum yield is rather low (<10 %), which is likely caused by the rather large Stokes shift. In addition, temperature-dependent emission spectra were recorded to determine the thermal quenching curve and the respective quenching temperature. Full article

Quasi-2D materials have received much attention in recent years for their unusual physical properties. Among the most investigated of these materials are the rare-earth tellurides, which are primarily studied because they exhibit charge density waves and other quantum phenomena and have a high degree of tunability. In this paper, we examine the optical and magnetic properties of several rare-earth tellurides and find that they are antiferromagnetic materials with hyperbolic dispersion. Hyperbolic materials have very promising applications in sub-diffraction-limit optics, nanolithography, and spontaneous emission engineering, but these applications are hampered by low-quality hyperbolic materials. Rare-earth tellurides may provide insight into solving these issues if their properties can be properly tuned using the large variety of techniques already explored in the literature. Full article

The density functional theory was used to explore the structural, electronic, dynamical, and thermoelectric properties of a VIrSi half-Heulser (HH) alloy. The minimum lattice constant of 5.69 $(\AA )$ was obtained for VIrSi alloy. The band structure and the projected density of states for this HH alloy were calculated, and the gap between the valence and conduction bands was noted to be 0.2 eV. In addition, the quasi-harmonic approximation was used to predict the dynamical stability of the VIrSi HH alloy. At 300 K, the Seebeck coefficient of 370 and −270 $\mathsf{\mu }$V.K${}^{-1}$, respectively, was achieved for the p and n-type doping. From the power factor result, the highest peak of 18 × 10${}^{11}$ W/cm.K${}^2$ is obtained in the n-type doping. The Figure of Merit (ZT) result revealed that VIrSi alloy possesses a high ZT at room temperature, which would make VIrSi alloy applicable for thermoelectric performance. Full article

Despite the large misfit dislocation densities, indium gallium nitride (InGaN) demonstrates high luminous efficiency both for electroluminescence and photoluminescence. The mechanism behind it has been interpreted as the existence of potential minima (i.e., localized states), which will screen the non-radiative recombination centers to avoid carriers being trapped by the defects. The existence of localized states has been testified by many experiments. However, almost all of the observations are indirect observations, and some experiments, such as those focused on whether the indium clusters observed by transmission electron microscopy are localized states, still remain controversial. Here, we report the direct observation of carrier transportation between localized states driven by temperature-dependent photoluminescence (TDPL) and excitation power-dependent PL in InGaN quantum wells. This enriches the experimental evidence on the existence of localized states. Full article

3,5-Dihydroxyphenyl-5-(dimethylamino)naphthalene-1-sulfonate, also referred to as sensor R1, was synthesized and characterized by ¹H- and ¹³C-NMR, IR, HRMS, and single-crystal X-ray diffraction. Connections in the packing crystal structure of sensor R1 occur through hydrogen bonding interactions. However, no π-π stacking interactions between molecules of sensor R1 were observed. Addition of fluoride ion to a solution of sensor R1 resulted in the appearance of a new absorption band at 310 nm, which corresponded to the deprotonated species, and quenching of the peak at an emission wavelength of 562 nm. For the addition of other anions, there was a slight decrease in corresponding peaks in the UV-visible and emission spectra of sensor R1. According to the ¹H-NMR study, the aromatic proton resonances of sensor R1 shifted upfield when adding fluoride ion. Analysis of the solutions prepared using Job’s method revealed that the complexation ratio of the complex formed between sensor R1 and fluoride ion was 1:1. The Stern−Volmer quenching constant (K_sv) between sensor R1 and fluoride ion was characterized as 7157 M⁻¹. Full article

In this work, we report first-principles calculations to study FeVO${}_4$ in the CrVO${}_4$-type (phase II) structure under pressure. Total-energy calculations were performed in order to analyze the structural parameters, the electronic, elastic, mechanical, and vibrational properties of FeVO${}_4$-II up to 9.6 GPa for the first time. We found a good agreement in the structural parameters with the experimental results available in the literature. The electronic structure analysis was complemented with results obtained from the Laplacian of the charge density at the bond critical points within the Quantum Theory of Atoms in Molecules methodology. Our findings from the elastic, mechanic, and vibrational properties were correlated to determine the elastic and dynamic stability of FeVO${}_4$-II under pressure. Calculations suggest that beyond the maximum pressure covered by our study, this phase could undergo a phase transition to a wolframite-type structure, such as in CrVO${}_4$ and InVO${}_4$. Full article

The physical and mechanical properties of an entirely (wrought alloys) or partly (cast alloys) dendritically solidified alloy strongly depend on the secondary dendrite arm spacing (SDAS). The casting practice and the simulation of solidification need a usable but simple method to calculate the SDAS during and at the end of solidification as a function of the cooling rate. Based on many solidification experiments, a simple equation to calculate the SDAS (empirical method) is known to use the local solidification time, which can be obtained from the measured cooling curves (equiaxed solidification), or can be calculated from the temperature gradient and front velocity (directional solidification). This equation is not usable for calculating the SDAS during solidification. Kirkwood developed a semi-empirical method based on the liquid phase’s diffusion, which contains only one geometric factor that seems constant for different alloys. This equation contains some physical parameters that depend on the temperature, so the equation cannot be integral in closed form. In the present work, first, we show the effect of the curvature of the solid/liquid interface on the equilibrium concentrations and then the different processes of SDA coarsening. In our earlier paper, we demonstrated that using the empirical method, the final SDAS can be calculated with acceptable correctness in the case of four unidirectional solidification experiments of Al-7wt%Si alloy. The present work shows that numerically integrated Kirkwood’s equations used the known cooling curve; the SDAS can be calculated at the end and during solidification in good agreement with these experimental results. Compared to the two calculation methods, we stated that the correctness of the methods is similar. Still, the results of the solidification simulation (the microsegregation) will be more correct using the dynamical method. It is also shown that with the dynamical method, the SDAS can be calculated from any type of cooling curve, and using the dynamical method, it is proved that some different SDASs could belong to the same local solidification time. Full article

The quasi-one-dimensional material PdTeI exhibits unusual electronic transport properties at ambient pressure. Here, we systematically investigate both the structural and electronic responses of PdTeI to external pressure, through a combination of electrical transport, synchrotron X-ray diffraction (XRD), and Raman spectroscopy measurements. The charge density wave (CDW) order in PdTeI is fragile and the transition temperature T_CDW decreases rapidly with the application of external pressure. The resistivity hump is indiscernible when the pressure is increased to ~1 GPa. Upon further compression, the resistivity dropping is observed approximately ~15 GPa and zero resistance is established above ~20 GPa, suggesting the occurrence of superconductivity. Combined XRD and Raman data evidence that the emergence of superconductivity is accompanied by a pressure-induced amorphization of PdTeI. Full article

We report on microfabrication and optical characterization of buried channel waveguides defined in Nd:YCOB crystal by focused proton beam writing (PBW). In the fabrication process, the focused proton beam irradiation creates a local material modification region with geometrically symmetric positive index changes at the end of the proton trajectory, where efficient optical waveguiding can be locally supported within a fiber-like channel structure. The impact of the proton fluence (with different values ranging from 10¹⁵ to 10¹⁶ cm⁻²) on the optical waveguiding performance is well studied. The experimental results of the optical waveguide properties are in fairly good agreement with the simulation results. Full article

Thin films of Ti-Al-Cr-N were deposited onto glass substrates by means of the reactive magnetron co-sputtering of pure Cr and TiAl alloy targets in an atmosphere of Ar and N₂. This investigation was carried out by adjusting the Cr-target power in order to increase the Cr amount in the films. The crystal structure of the films was investigated via X-ray diffraction (XRD). The elemental composition of the coatings was determined using Auger electron spectroscopy (AES). The electrical resistivity was measured using the four-point probe method, and the optical properties were characterized via ultraviolet/visible (UV/Vis) spectroscopy. The experimental results showed that, with a Cr concentration between 0 at% and 11.6 at%, a transition between phases from a single-phase hexagonal wurtzite-type structure to a single-phase cubic NaCl-type structure took place. The addition of Cr increased the crystallite size and, with it, the roughness of the coatings. All of the coatings exhibited an ohmic behavior at room temperature, and their surface electrical resistivity decreased from 490.1 ± 43.4 Ωcm to 1.5 ± 0.1 Ωcm as the chromium concentration increased. The transmittance of the coatings decreased, and the optical band gap (Egap) went from 3.5 eV to 2.3 eV with the addition of Cr. These electrical and optical properties have not been previously reported for these films. Full article

The graphene-based nano-mechanical systems have attracted a lot of attention due to their unique properties. Owing to its planar shape, it is hard to control the direction of motion of graphene. In this study, a directional system based on graphene with a channel driven by a thermal gradient was examined by means of molecular dynamics simulations. The results showed that the channel could direct the motion and correct the rotation of graphene nanoflakes. The movement of graphene nanoflake not only depended on the interaction between the nanoflake and the substrate, but also the configuration of the graphene in the channel. A larger thermal gradient was needed to drive a hydrogen-passivated graphene nanoflake. However, the movement of a passivated nanoflake was more stable. Our results showed that a passivated graphene nanoflake could move steadily along a direction in a channel, which might shed light on the design of nano-mechanical systems based on graphene. Full article

Gemstones usually contain inclusions as the natural hallmark of their formation. Studies on inclusions may contribute to our understanding of the gem and better adapt to the gems and jewelry industry. In this study, we applied advanced 3D Raman mapping and high-resolution X-ray computed tomography (HRXCT) and conducted a thorough experiment on one emerald with a special trapiche pattern containing a colorless core, solid minerals, and fluids. Hematite and magnetite were identified as metallic minerals by the Raman spectrum. The hexagonal core is beryl, and the voids are primarily filled with CO₂ and N₂. HRXCT demonstrated a visualized distribution of these inclusions within the gem host by reconstructing a 3D illustration. Further calculation of the volume of inclusions regarding the host showed that the minerals take up 0.07%, void 0.03%, and the hexagonal core 8.25%. The combined application of Raman-Mapping and X-ray Micro Computed Tomography proved to be a very promising technique for tracing the gemstones by characterizing the unique inclusions (identification and morphology) within the gem host. Full article

The Al-Si-Cr-Co-Ni High Entropy Alloy (HEA) with low density (about 5.4 g/cm³) and excellent performance had significant potential in the lightweight engineering material field. To further research and optimize the Al-Si-Cr-Co-Ni system HEA, the influences of element Cr on the microstructures and performances of lightweight AlSi_0.5Cr_xCo_0.2Ni (in mole ratio, x = 1.0, 1.2, 1.4, 1.6, and 1.8) HEAs were investigated. The experiment results manifested that AlSi_0.5Cr_xCo_0.2Ni HEAs were composed of A2 (Cr-rich), B2 (Ni-Al), and Cr₃Si phases, indicating that the addition of Cr did not result in the formation of a new phase. However, ample Cr increased the Cr₃Si phase composition, further ensuring the high hardness (average HV 981.2) of HEAs. Electrochemical tests demonstrated that HEAs with elevated Cr₃Si and A2 phases afforded greater corrosion resistance, and the improvement in corrosion was more pronounced when x > 1.6. This work is crucial in the development of lightweight engineering HEAs, which are of tremendous practical utility in the fields of cutting tools, hard coating, etc. Full article

The effect of rod-like nanoparticles on the high-frequency dielectric susceptibility of the nematic nano-composites has been investigated in the framework of a molecular theory. Analytical expressions for the components of the effective polarizability of a rod-like nanoparticle in the nematic host have been obtained and used in the calculations of the dielectric susceptibility of the composites as functions of the nanoparticle volume fraction. Numerical calculations of the susceptibility have been undertaken using the nematic liquid crystal 5CB as a host doped with either gold or silver particles for different values of the concentration of nanoparticles. It has been shown that the rod-like nanoparticles have a much stronger effect on the components of the dielectric susceptibility of the nano-composites including, in particular, the one with gold nanoparticles in the vicinity of the plasmon resonance. The main conclusion is that at sufficiently large concentration of nanoparticles, the anisotropy of the dielectric susceptibility of the nano-composites may even change the sign with an increasing concentration which may be important for various applications. Full article

In this work, dewetting process has been investigated in shape-memory Heuslers. To this aim, series of high-temperature annealing (1100–1150 K) have been performed at high vacuum (time is varied in the range of 55–165 min) in Ni-Mn-Ga epitaxial thin films grown on MgO(001). The process kinetics have been followed by studying the evolution of morphology and composition. In particular, we report the initiation of the dewetting process by the formation of symmetric holes in the films. The holes propagate and integrate, leaving micrometric and submicron islands of the material, increasing the average roughness of the films by a factor of up to around 30. The dewetting process is accompanied by severe Ga and Mn sublimation, and Ni-Ga segregation, which significantly modify the magnetic properties of the films measured at each stage. The annealed samples show a relatively weak magnetic signal at room temperature with respect to the pristine sample. Full article

In this research, ZnO/GO nanocomposites were successfully synthesized by a simple hydrothermal method using graphene oxide (GO) and zinc acetate dihydrate (Zn(CH₃COO)₂.2H₂O) as the reactants. The effect of the hydrothermal reaction time on the structure and optical property of the ZnO/GO was systematically investigated. The structure, morphology and chemical composition of the samples were measured by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and Raman and Fourier transform infrared (FTIR) spectroscopy, while the optical properties were measured using photoluminescence spectroscopy. The synthesized products consisted of large quantities of one-dimensional (1D) ZnO nanorods (NRs), which were dispersed uniformly on the GO surface. The XRD and Raman results reveal that the ZnO NRs in the fabricated samples had a hexagonal wurtzite structure with high crystalline quality. The FESEM and TEM images reveal that ZnO NRs with an average diameter in the range of ~85–270 nm and length in the range of ~0.3–6 μm were covered with GO sheets. Additionally, it was found that the crystallographic orientation of ZnO NRs was dependent not only on the hydrothermal reaction time but also on the presence of GO in the nanocomposites. However, the addition of GO did not affect the stoichiometric ratio and the crystal structure of ZnO NRs. The room-temperature PL results indicated that, compared to those of pure ZnO, the luminescence of the GO/ZnO nanocomposites was suppressed and shifted towards a higher wavelength (red shift), which was attributed to the incorporation of ZnO NRs within the GO matrix and the formation of a C-O-Zn chemical bond in the nanocomposites. The hydrothermal technique is considered one of the best routes due to its low cost, high growth rates, low-temperature synthesis, controllable crystallographic orientation, particle size, as well as morphology. Full article

Chemical vapor deposition (CVD) diamond crystal is considered as an ideal material platform for Raman lasers with both high power and good beam quality due to its excellent Raman and thermal characteristics. With the continuous development of CVD diamond crystal growth technology, diamond Raman lasers (DRLs) have shown significant advantages in achieving wavelength expansion with both high beam quality and high-power operation. However, with the output power of DRLs reaching the kilowatt level, the adverse effect of the thermal impact on the beam quality is progressively worsening. Aiming to enunciate the underlying restrictions of the thermal effects for high-power DRLs (e.g., recently reported 1.2 kW), we here establish a thermal-structural coupling model, based on which the influence of the pump power, cavity structure, and crystal size have been systematically studied. The results show that a symmetrical concentric cavity has less thermal impact on the device than an asymmetrical concentric cavity. Under the ideal heat dissipation condition, the highest temperature rise in the diamond crystal is 23.4 K for an output power of ~2.8 kW. The transient simulation further shows that the heating and cooling process of DRLs is almost unaffected by the pump power, and the times to reach a steady state are only 1.5 ms and 2.5 ms, respectively. In addition, it is also found that increasing the curvature radius of the cavity mirror, the length and width of the crystal, or decreasing the thickness of the crystal is beneficial to alleviating the thermal impact of the device. The findings of this work provide some helpful insights into the design of the cavity structure and heat dissipation system of DRLs, which might facilitate their future development towards a higher power. Full article

Despite chalcopyrite (CuFeS${}_2$) being one of the oldest known copper ores, it exhibits various properties that are still the subject of debate. For example, the relative concentrations of the ionic states of Fe and Cu in CuFeS${}_2$ can vary significantly between different studies. The presence of a plasmon-like resonance in the visible absorption spectrum of CuFeS${}_2$ nanocrystals has driven a renewed interest in this material over recent years. The successful synthesis of CuAl${}_{1-p}$Fe${}_p$S${}_2$ nanocrystals that exhibit a similar optical resonance has recently been demonstrated in the literature. In this study, we use density functional theory to investigate Fe substitution in CuAlS${}_2$ and find that the formation energy of neutral ${\left[{\mathrm{Fe}}_{\mathrm{Cu}}\right]}^{2+}+{\left[{\mathrm{Cu}}_{\mathrm{Al}}\right]}^{2-}$ defect complexes is comparable to ${\left[{\mathrm{Fe}}_{\mathrm{Al}}\right]}^0$ antisites when $p\ge 0.5$. Analysis of electron density and density of states reveals that charge transfer within these defect complexes leads to the formation of local Cu${}^{2+}$/Fe${}^{2+}$ ionic states that have previously been associated with the optical resonance in the visible absorption of CuFeS${}_2$. Finally, we comment on the nature of the optical resonance in CuAl${}_{1-p}$Fe${}_p$S${}_2$ in light of our results and discuss the potential for tuning the optical properties of similar systems. Full article

The critical roles of short-range ordering (SRO) in the grain boundary character distribution (GBCD) optimization of Ni-Cr alloys with high stacking fault energies were experimentally studied by thermomechanical treatments. It is found that, with the enhancement of the SRO degree (or the increase in Cr content), the dislocation slip mode changes from wavy slip to planar slip, and even deformation twins (DTs) appear in the cold-rolled Ni-40at.%Cr alloy. Within the lower level of Cr content (≤20 at.%), the optimized result of GBCD is conspicuous with the increase in Cr content. As the Cr content is higher than 20 at.%, the GBCD optimization of Ni-Cr alloys cannot be further enhanced, since the cold rolling induced DTs would hinder the growth of twin related domains during subsequent annealing. Full article