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Finite size scaling for a first order phase transition, where a continuous symmetry is broken, is tested using an approximation of Gaussian probability distributions with a phenomenological "degeneracy" factor. Predictions are compared to the data from Monte Carlo simulations of the Lebwohl–Lasher model on L × L × L simple cubic lattices. The data show that the intersection of the fourth-order cumulant of the order parameter for different lattice sizes can be expressed in terms of the relative degeneracy q = 4π of the ordered and disordered phases. This result further supports the concept of universality at first order transitions developed recently. [ABSTRACT FROM AUTHOR]

The effect of cadmium ions introduced into fluorophosphate glass on the growth and photoluminescence (PL) of the CsPb1–xCdxBr3 perovskite nanocrystals (NCs) is systematically studied. The x-ray diffraction patterns have shown that cadmium ions are really incorporated into the NCs that results in a decrease in the lattice constant from 5.85 (x = 0) to 5.75 Å (x = 0.45). At the large cadmium content in the glass (x > 0.38), simultaneous formation of the perovskite CsPb1–xCdxBr3 NCs and the non-luminescent CsCdBr3 NCs in the hexagonal phase is found. It is also found that the lattice contraction leads to an increase in the bandgap energy and a noticeable shift of the PL band to the blue region of the spectrum (from 2.42 to 2.68 eV) with a drop in quantum yield from 85% for CsPbBr3 NCs down to 4% for CsPb0.55Cd0.45Br3 NCs. It is shown that the PL quantum yield decreases due to the formation of deep trap states, which manifest themselves as a PL band in the energy range of 1.6–2.5 eV at cryogenic temperatures. A simple model explaining the behavior of the PL band as a function of temperature in the range from 30 to 300 K is proposed. [ABSTRACT FROM AUTHOR]

The B20 type chiral magnet FeGe exhibits the formation of skyrmion-lattice (SkL) phases in the vicinity of the magnetic ordering temperature. The SkL is a magnetic superlattice composed of vortex-type topological spin objects, and it has experimentally been known that its formation requires the existence of an intermediate (IM) phase between SkL and the paramagnetic (PM) phases. We take interest in how the crystal lattice experiences the formation of these topological spin texture. In this study, we observed the so-called spin–orbit coupling induced magnetostriction related to these topological spin texture formation, in addition to the ac magnetization anomalies. The temperature and magnetic field dependences of the lattice parameter reflected the transformation of phases, such as helimagnetic (HM), SkL, IM, conical (CM), and PM phases. In the PM region, a phase characterized as gaseous skyrmions was detected similarly to the case of the same B20 type MnSi. Furthermore, the HM, CM, and IM phases were also divided into two regions. Thus, the precise phase diagram near T c was reconstructed from the prospect of the magnetostriction such that we demonstrated that the stabilization of skyrmions needs a finite magnetic field. [ABSTRACT FROM AUTHOR]

Laser annealing was employed to trigger the solid-state reaction of a thin Co film (2.5 nm) with undoped Si. A metastable disilicide layer was obtained after one laser pulse close to the melt threshold. Its diffraction pattern, relaxed lattice parameter, and residual resisitivity are consistent with the formation of the defective CsCl structure. The CoSi2 phase was found after prolonging the thermal treatment with additional pulses or rapid thermal annealing. Because CoSi is skipped in the phase sequence, CoSi2 layers are more uniform in thickness, have an increased superconductivity and a reduced formation temperature. This approach is compatible with the SALICIDE process and can be used to form smooth contacts in superconducting or regular transistors. [ABSTRACT FROM AUTHOR]

The pyrite phase of sodium superoxide, NaO 2 , is studied using equilibrium molecular dynamics simulations and lattice dynamics calculations to understand the impacts of static disorder and dynamic disorder on its thermal conductivity. Three structural regimes are observed based on the rotational dynamics and orientations of O 2 − ions. At low temperatures, where the O 2 − ions librate and the system is fully ordered, thermal conductivity exhibits a crystal-like temperature dependence, decreasing with increasing temperature. As temperature increases, the static disorder regime emerges, where the O 2 − ions transition between different orientations on a time scale larger than the librational period. In this regime, the thermal conductivity continues to decrease and then becomes temperature independent. At higher temperatures, where the O 2 − ions freely rotate, the system is dynamically disordered and the thermal conductivity is temperature independent, as in an amorphous solid. Using instantaneous normal mode analysis and Allen–Feldman theory, 80% of the thermal conductivity in the dynamic disorder regime is attributed to diffusons, vibrational modes that are non-propagating and non-localized. When increasing the lattice constant at a constant temperature, transitions from librations to static disorder to dynamic disorder are also observed, with the thermal conductivity decreasing monotonically. The presented methodology can be applied to other crystals with rotational degrees of freedom, offering strategies for the design of thermal conductivity switches that are responsive to external stimuli. [ABSTRACT FROM AUTHOR]

Recent developments in materials manufacturing has allowed researchers to engineer unique wave-matter interactions at the nano-scale. These interactions foster unique and coupled modes of thermal, optical, electrical, and acoustic energy transport and conversion. This study addresses the sensitivity of the static ϵ 0 and complex ϵ ~ (ω) = ϵ 1 (ω) + i ϵ 2 (ω) dielectric constant due to changes in pressure (P), volume (V), and temperature (T). General β -sensistivity relations are derived based on traditional Drude and Lorentz oscillator models. Then, these sensitivity relations are compared to literature d ln ⁡ ϵ i / d T and d ln ⁡ ϵ i / d ln ⁡ V data for various metals, dielectric insulators, and semiconductor materials. For example, the effects of isotropic strain on ϵ (ω) are found to have two common contributions: the frequency dependence of the dielectric dispersion (d ln ⁡ ϵ / d ln ⁡ ω) and key vibrational-mode Grüneisen parameters (γ i = − d ln ⁡ ω i / d ln ⁡ V). Because these sensitivity relations are dictated by the various electronic, optical, and lattice Grüneisen parameters, a comprehensive listing of mode Grüneisen parameters and coupled property data are provided for materials ranging from metals to semiconductors to polymers to dielectric insulators such as BaTiO 3. In most cases, the developed sensitivity relations are consistent with published isotropic strain derivative data. [ABSTRACT FROM AUTHOR]

The pyrite phase of sodium superoxide, NaO 2 , is studied using equilibrium molecular dynamics simulations and lattice dynamics calculations to understand the impacts of static disorder and dynamic disorder on its thermal conductivity. Three structural regimes are observed based on the rotational dynamics and orientations of O 2 − ions. At low temperatures, where the O 2 − ions librate and the system is fully ordered, thermal conductivity exhibits a crystal-like temperature dependence, decreasing with increasing temperature. As temperature increases, the static disorder regime emerges, where the O 2 − ions transition between different orientations on a time scale larger than the librational period. In this regime, the thermal conductivity continues to decrease and then becomes temperature independent. At higher temperatures, where the O 2 − ions freely rotate, the system is dynamically disordered and the thermal conductivity is temperature independent, as in an amorphous solid. Using instantaneous normal mode analysis and Allen–Feldman theory, 80% of the thermal conductivity in the dynamic disorder regime is attributed to diffusons, vibrational modes that are non-propagating and non-localized. When increasing the lattice constant at a constant temperature, transitions from librations to static disorder to dynamic disorder are also observed, with the thermal conductivity decreasing monotonically. The presented methodology can be applied to other crystals with rotational degrees of freedom, offering strategies for the design of thermal conductivity switches that are responsive to external stimuli. [ABSTRACT FROM AUTHOR]

This work reports heavy ion-irradiation effects in polycrystalline Fe3O4. For this matter, Fe/Fe3O4 heterostructures were irradiated in situ in a transmission electron microscopy with 1 MeV Kr ions at 50 K. Evidence of cubic to monoclinic transformation (a.k.a Verwey transition) was recorded in some magnetite grains upon cooling the sample (around 90 K); however, most of the oxide grains retain their cubic spinel structure. Irradiation effects were analyzed in the cubic phase up to a maximum dose of 38 dpa without the sign of amorphization. The extinction of first-order reflections was recorded at doses below 1 dpa, indicating the formation of a new (metastable) phase with half of the lattice parameters compared to the unirradiated Fe3O4 crystal. The formation of the new crystalline phase, which also presents a high resistance to amorphization, is related to the disordering of the cation lattice and the high mobility of the cation interstitials. The metastable phase readily recovers around 225 K during the natural warming of the sample from 50 K to room temperature. [ABSTRACT FROM AUTHOR]

In this numerical study, we propose dual-modulated topological pillared phononic crystal (PnC) plates and demonstrate their application in achieving frequency-selective waveguiding of Lamb-wave valley-edge states. We show that both the radius and the height of the pillars in the honeycomb unit cell can be varied, allowing a generalized parameter space to obtain the complete topological bandgaps and two groups of distinct valley Hall phases for designing topological waveguides operating in different frequency ranges. Accordingly, we construct different types of phase domain walls to support valley-edge states using the dual-modulated PnC plates with a lattice constant of 2000 μm and with topological bandgaps opened around the Dirac cone frequency of 426 kHz. The numerical results show that the valley-edge states emerge to cover different frequency ranges and exhibit robust backscattering immunity when propagating along zigzag paths with sharp corners. Furthermore, the transport path of the valley-edge states can be designed to be highly dependent on the operating frequency in different domain walls. Consequently, we design a straight waveguide and three multichannel waveguides to demonstrate frequency-dependent switchable transmission and selective channeling of valley-edge states, respectively. The results of this study pave the way for the development and optimization of topological acoustic circuits using the generalized parameter space approaches and are expected to find promising applications in frequency-controlled and signal-division devices. [ABSTRACT FROM AUTHOR]

In this work, we derive the analytical expression of Helmholtz free energy, mean nearest neighbor distance between two atoms, lattice constant, and molar volume using statistical moment method (SMM). Then, we present how to determine the melting temperature of cubic perovskite at high pressures by combining SMM and work-heat equivalence principle. The results of the melting theory of cubic perovskite are applied to two perovskites MgSiO 3 and CaSiO 3 under extreme conditions of the Earth's lower mantle. Our obtained melting curves of MgSiO 3 up to 1400 GPa and CaSiO 3 up to 136 GPa were compared with available experiment and other calculations and were in good agreement. The present study provides an effective theoretical tool for finding the melting curves of strongly anharmonic materials under extreme conditions. Our theoretical calculations would be helpful to clarify geological formation process at the Earth's lower mantle. [ABSTRACT FROM AUTHOR]

We investigated the structure of ice under nanoporous confinement in periodic mesoporous organosilicas (PMOs) with different organic functionalities and pore diameters between 3.4 and 4.9 nm. X-ray scattering measurements of the system were performed at temperatures between 290 and 150 K. We report the emergence of ice I with both hexagonal and cubic characteristics in different porous materials, as well as an alteration of the lattice parameters when compared to bulk ice. This effect is dependent on the pore diameter and the surface chemistry of the respective PMO. Investigations regarding the orientation of hexagonal ice crystals relative to the pore wall using x-ray cross correlation analysis reveal one or more discrete preferred orientation in most of the samples. For a pore diameter of around 3.8 nm, stronger correlation peaks are present in more hydrophilically functionalized pores and seem to be connected to stronger shifts in the lattice parameters. [ABSTRACT FROM AUTHOR]

Magnetic structure factor (MSF), calculated from ground state configuration previously obtained by Monte Carlo simulation in different rectangular artificial spin ices, is employed to investigate ground state degeneracy. Our analysis considers the importance of nanoislands size to the ratio between rectangle sides in the lattice parameters via a dumbbell model. Pinch points in MSF along with residual entropy, determined for a number of different rectangular lattices with disconnected nanoislands, point out the conditions for the emergency of a gauge field, through which magnetic monopoles interact effectively. [ABSTRACT FROM AUTHOR]

We find that the unit cell volume (V), which affects many properties, decreases too rapidly with strain when calculated with standard density functional theories (DFTs) such as local density approximation (LDA). We find that this demerit is moderated with the use of the Hubbard potential U for local electron correlation (DFT + U). However, the introduction of U to standard DFTs, e.g., LDA and Perdew–Burke–Ernzerhof functional (PBE) optimized for solids (PBEsol), leads to the excessive underestimation of the spontaneous polarization (PS) and frequently extinguishes PS. Therefore, we attempt to improve the overall accuracy of DFTs for ferroelectrics by using U in several DFT methods including PBE that overestimates PS and lattice constants. We demonstrate that PBE with U (PBE + U) is in excellent agreement with the experimental properties of BaTiO3 and SrTiO3, with improvements in the estimates of lattice constants, PS, the phonon frequency, the antiferrodistortive angle of 105 K-phase SrTiO3, the bandgap, the strain dependence of V, and hole polarons. When the lattice parameters and PS moderately agree with the experimental data, PBE + U with a single U set can produce both electron and hole polarons. Hence, PBE + U can be a practical substitute of hybrid functionals for perovskite oxide ferroelectrics, except for the estimation of the bandgap. Furthermore, we propose an approach to construct a functional accurately depicting the incipient ferroelectric state of SrTiO3. Additionally, these results suggest that conventional DFT underestimates PS under compressive in-plane strain and predicts the unrealistic deformation of ferroelectrics and that in-plane-strained lattices can mitigate the problems associated with U. [ABSTRACT FROM AUTHOR]

Hyperbolic metasurfaces exhibit unique dispersion and polarization properties, making them a promising platform for a plethora of photonic applications. At the same time, the ability to engineer the hyperbolicity via the predefined spectral positions of the metasurface resonances remains a notable challenge. Here, we analyze the dependencies of the spectral positions of the resonances corresponding to the limits of the hyperbolic regime for the metasurfaces based on square arrays of the rectangular nanopatches. We show that the spectral difference between the resonances increases linearly with stretching of the nanopatch, but this dependence becomes quadratic when the length of the stretched nanopatch exceeds 85% of the lattice constant, indicating the regime of extreme anisotropy. Finally, we demonstrate the characteristic feature of the engineered resonances by showing the canalization (divergenceless propagation) of the surface plasmon-polariton along the anisotropic nanopatch-based metasurface in the vicinity of the resonance. The results obtained may be used for the engineering of the anisotropic nanoparticle-based metasurfaces for a plethora of photonic applications. [ABSTRACT FROM AUTHOR]

In multicomponent lattice problems, for example, in alloys and at crystalline surfaces and interfaces, atomic arrangements exhibit spatial correlations that dictate the kinetic and thermodynamic phase behavior. These correlations emerge from interparticle interactions and are frequently reported in terms of the short-range order (SRO) parameter. Expressed usually in terms of pair distributions and other cluster probabilities, the SRO parameter gives the likelihood of finding atoms/molecules of a particular type in the vicinity of other atoms. This study focuses on fundamental constraints involving the SRO parameters that are imposed by the underlying lattice topology. Using a data-driven approach, we uncover the interrelationships between different SRO parameters (e.g., pairs, triplets, and quadruplets) on a lattice. The main finding is that while some SRO parameters are independent, the remaining are collinear, i.e., the latter are dictated by the independent ones through linear relationships. A kinetic and thermodynamic modeling framework based on these constraints is introduced. [ABSTRACT FROM AUTHOR]

Spin–orbit coupling induces a current density in the ground state, which consequently requires a generalization for meta-generalized gradient approximations. That is, the exchange–correlation energy has to be constructed as an explicit functional of the current density, and a generalized kinetic energy density has to be formed to satisfy theoretical constraints. Herein, we generalize our previously presented formalism of spin–orbit current density functional theory [Holzer et al., J. Chem. Phys. 157, 204102 (2022)] to non-magnetic and magnetic periodic systems of arbitrary dimension. In addition to the ground-state exchange–correlation potential, analytical derivatives such as geometry gradients and stress tensors are implemented. The importance of the current density is assessed for band gaps, lattice constants, magnetic transitions, and Rashba splittings. In the latter, the impact of the current density may be larger than the deviation between different density functional approximations. [ABSTRACT FROM AUTHOR]

Emerging quantum materials as well as novel traditional electronic and photonic materials may enable a new generation of information science devices if they can be synthesized on suitable substrates. Additionally, material and device designs may benefit from tunable properties through engineered epitaxial strain for the manipulation of the electronic character. In this work, three series of III–V ternary alloys, GaInSb, AlInSb, and InAsSb, are grown via molecular beam epitaxy on GaAs (001) substrates to explore the flexibility of abrupt metamorphic epitaxial layers with tunable lattice parameters between 6.135 and 6.479 Å. Their deposition on both homomorphic GaAs and pseudomorphic AlAs buffers is also explored. The structures of these alloys are characterized via reflection high-energy electron diffraction, high-resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy to assess their suitability as stable buffer layers with wide variability of accessible lattice parameters. [ABSTRACT FROM AUTHOR]

Molecular dynamics and density functional theory simulations are used to predict the lattice and electronic contributions of thermophysical properties for UN, PuN, and mixed (U,Pu)N systems. The properties predicted include the lattice parameter, linear thermal expansion, enthalpy, and specific heat capacity, as a function of temperature. The simulation predictions for high temperature specific heat capacity are compared against experimental measurements to understand the behavior, and why differences in the experimental measurements are observed. The influence of adding U vacancies, N interstitials, and Pu to UN is also examined. For this, a new PuN potential parameter set is developed and used with the Kocevski UN potential, enabling the dynamics of mixed (U,Pu)N systems to be studied. How defects impact the thermophysical properties is important for understanding fuel behavior under different reactor conditions, and these mechanistic predictions can be used to support fuel performance codes where data is scarce. [ABSTRACT FROM AUTHOR]

This work outlines conditions suitable for the heteroepitaxial growth of Cr2O3(0001) films (1.5–20 nm thick) on a Ru(0001)-terminated substrate. Optimized growth is achieved by sputter deposition of Cr within a 4 mTorr Ar/O2 20% ambient at Ru temperatures ranging from 450 to 600 °C. The Cr2O3 film adopts a 30° rotated honeycomb configuration with respect to the underlying Ru(0001) substrate and exhibits a hexagonal lattice parameter consistent with that for bulk Cr2O3(0001). Heating to 700 °C within the same environment during film preparation leads to Ru oxidation. Exposure to temperatures at or above 400 °C in a vacuum, Ar, or Ar/H2 3% leads to chromia film degradation characterized by increased Ru 3d XPS intensity coupled with concomitant Cr 2p and O 1s peak attenuations when compared to data collected from unannealed films. An ill-defined but hexagonally well-ordered RuxCryOz surface structure is noted after heating the film in this manner. Heating within a wet Ar/H2 3% environment preserves the Cr2O3(0001)/Ru(0001) heterolayer structure to temperatures of at least 950 °C. Heating an Ru–Cr2O3–Ru heterostacked film to 950 °C within this environment is shown by cross-sectional scanning/transmission electron microscopy (S/TEM) to provide clear evidence of retained epitaxial bicrystalline oxide interlayer structure, interlayer immiscibility, and epitaxial registry between the top and bottom Ru layers. Subtle effects marked by O enrichment and O 1s and Cr 2p shifts to increased binding energies are noted by XPS in the near-Ru regions of Cr2O3(0001)/Ru(0001) and Ru(0001)/Cr2O3(0001)/Ru(0001) films after annealing to different temperatures in different sets of environmental conditions. [ABSTRACT FROM AUTHOR]

Nonvolatile memory using intersubband transitions and quantum-well electron accumulation in GaN/AlN resonant tunneling diodes (RTDs) is a promising candidate for high-speed nonvolatile memory operating on a picosecond timescale. This memory has been fabricated on sapphire(0001) substrates to date because of the high affinity between the nitride materials and the substrate. However, the fabrication of this memory on Si(111) substrates is attractive to realize hybrid integration with Si devices and nonvolatile memory and three-dimensional integration such as chip-on-wafer and wafer-on-wafer. In this study, GaN/AlN RTDs are fabricated on a Si(111) substrate using metal-organic vapor phase epitaxy. The large strain caused by the differences in the thermal expansion coefficients and lattice constants between the Si(111) substrate and nitride materials are suppressed by a growth technique based on the insertion of low-temperature-grown AlGaN and thin AlN layers. The GaN/AlN RTDs fabricated on Si(111) substrates show clear GaN/AlN heterointerfaces and a high ON/OFF ratio of >220, which are equivalent to those for devices fabricated on sapphire(0001) substrates. However, the nonvolatile memory characteristics fluctuate by repeated write/erase memory operations. Evaluation of the ON/OFF switching time and endurance characteristics indicates that the instability of the nonvolatile memory characteristics is caused by electron leakage through deep levels in the quantum-well structure. Possible methods for suppressing this are discussed with an aim of realizing high-speed and high-endurance nonvolatile memory. [ABSTRACT FROM AUTHOR]

Sc0.18Al0.82N/GaN with state-of-the-art x-ray diffraction figures of merit grown by metal modulated epitaxy under metal-rich conditions and a low substrate temperature of 400 °C is demonstrated to have improved crystalline order [250 arc sec for the (0002) reflection and 469 arc sec for the (10 1 ¯ 5)] compared to a previous state-of-the-art sample grown at a more conventional temperature of 650 °C. While both samples show a columnar structure, the higher substrate temperature sample has a good symmetric rocking curve (RC) of 229 arc sec, but unlike the lower temperature sample, the RC of the (10 1 ¯ 5) asymmetric reflection could not be measured, indicating a more columnar structure common among ScAlN films. Local lattice constant maps (LLCMs) from 4D-STEM depict abrupt strain relaxation within ∼2 nm from the ScAlN/GaN interface for the sample grown at Tsub = 400 °C. Since these LLCMs suggest a lattice mismatch in the a-lattice constant, and since the films show a sudden roughening, the composition for lattice match to GaN may be less than the accepted 18%–20% Sc, consistent with the average GaN lattice match from lattice constant values reported in the literature of 12%. Compared to traditional III-Nitrides, ScAlN films have substantially more screw and mixed-type threading dislocations, suggesting substantial shear forces that result in significant twist and distortion leading to orthorhombic diffraction patterns as viewed from plan-view TEM in the Tsub = 650 °C sample. These results offer the possibility of ScAlN integration into low-thermal-budget processes including CMOS but further indicate that structural understanding of ScAlN remains lacking. [ABSTRACT FROM AUTHOR]

The electronic structures of three highly mismatched alloys (HMAs)—GeC(Sn), Ga(In)NAs, and BGa(In)As—were studied using density functional theory with HSE06 hybrid functionals, with an emphasis on the local environment near the mismatched, highly electronegative atom (B, C, and N). These alloys are known for their counterintuitive reduction in the bandgap when adding the smaller atom, due to a band anticrossing (BAC) or splitting of the conduction band. Surprisingly, the existence of band splitting was found to be completely unrelated to the local displacement of the lattice ions near the mismatched atom. Furthermore, in BGaAs, the reduction in the bandgap due to BAC was weaker than the increase due to the lattice constant, which has not been observed among other HMAs but may explain differences among experimental reports. While local distortion in GeC and GaNAs was not the cause for BAC, it was found to enhance the bandgap reduction due to BAC. This work also found that mere contrast in electronegativity between neighboring atoms does not induce BAC. In fact, surrounding the electronegative atom with elements of even smaller electronegativity than the host (e.g., Sn or In) consistently decreased or even eliminated BAC. For a fixed composition, moving Sn toward C and In toward either N or B was always energetically favorable and increased the bandgap, consistent with experimental annealing results. Such rearrangement also delocalized the conduction band wavefunctions near the mismatched atom to resemble the original host states in unperturbed Ge or GaAs, causing the BAC to progressively weaken. These collective results were consistent whether the mismatched atom was a cation (N), anion (B), or fully covalent (C), varying only with the magnitude of its electronegativity, with B having the least effect. The effects can be explained by charge screening of the mismatched atom's deep electrostatic potential. Together, these results help explain differences in the bandgap and other properties reported for HMAs from different groups and provide insight into the creation of materials with designer properties. [ABSTRACT FROM AUTHOR]

We explore piezooptic and photoelastic properties of Ca3Ga2Ge4O14 (CGG) crystals. A Mach–Zehnder interferometry technique is utilized to determine a complete set of the piezooptic tensor constants πim, with particular attention to the measurement accuracy, reliability, and uncertainty resolution in the piezooptic measurements. For these reasons, independent piezooptic constants or their combinations were determined by performing interferometric measurements for different geometries of piezooptic coupling using samples of both principal (direct) and non-principal (X/45°) crystallographic cuts. Basing on the results of piezooptic measurements, a complete set of photoelastic tensor constants pim and the acousto-optic performance (figure of merit M2) of CGG crystals were evaluated. The obtained piezooptic, photoelastic, and acousto-optic characteristics of CGG crystals are compared with those of other crystals of the langasite group, langasite and CTGS (Ca3TaGa3Si2O14). A comparative analysis reveals a correlation between the values of the piezooptic or photoelastic constants and the lattice parameters for this group of crystals. High optical quality and optical transparency in the UV region of the spectrum up to 260 nm together with extremely high mechanical resistance to uniaxial compression (≤2000 kg/cm2) opens up the possibility for specific application of CGG crystal as an optical material for piezooptic sensors of high uniaxial compression. The presented piezooptic interference technique along with methodological and metrological approaches paves the way for accurate and unambiguous characterization of photoelastic crystal materials of trigonal symmetry. [ABSTRACT FROM AUTHOR]

Thermal transport in wurtzite aluminum nitride (w-AlN) significantly affects the performance and reliability of corresponding electronic devices, particularly when lattice strains inevitably impact the thermal properties of w-AlN in practical applications. To accurately model the thermal properties of w-AlN with high efficiency, we develop a machine learning interatomic potential based on the atomic cluster expansion (ACE) framework. The predictive power of the ACE potential against density functional theory (DFT) is demonstrated across a broad range of properties of w-AlN, including ground-state lattice parameters, specific heat capacity, coefficients of thermal expansion, bulk modulus, and harmonic phonon dispersions. Validation of lattice thermal conductivity is further carried out by comparing the ACE-predicted values to the DFT calculations and experiments, exhibiting the overall capability of our ACE potential in sufficiently describing anharmonic phonon interactions. As a practical application, we perform a lattice dynamics analysis using the potential to unravel the effects of biaxial strains on thermal conductivity and phonon properties of w-AlN, which is identified as a significant tuning factor for near-junction thermal design of w-AlN-based electronics. [ABSTRACT FROM AUTHOR]

Alloying and site ordering play complementary roles in dictating a material's properties. However, deconvolving the impacts of these separate phenomena can be challenging. In this work, we simulate structures of Zn (Sn , Ge) N 2 with varied Sn content and site ordering to determine the impacts of order and composition on structural and electronic properties. We assess the formation enthalpy, lattice parameters, elastic constants, spontaneous polarization, and piezoelectric coefficients. In mostly disordered structures (order parameters ranging from 0.2 to 0.4), the formation enthalpy exhibits local extrema as a function of the order parameter, deviating from the more linear trends seen in both fully disordered and fully ordered systems. This anomalous deviation from the otherwise linear trend in formation enthalpy with order manifests in each of the other properties calculated. This range of order parameters of interest may be caused by a transition in the ordering of the quaternary material similar to phase changes seen in ternary compounds but stretched over a region inclduing 20% of the order parameter range. Most parameters calculated are more sensitive to order than to composition in the limited composition range tested; however, the lattice parameter c , piezoelectric coefficient e 33 , and elastic moduli C 12 , C 13 , and C 23 are more sensitive to composition. Of the properties compared, the piezoelectric coefficients are influenced most significantly by changes in both the composition and order parameter. Lattice parameters undergo the smallest changes with order and composition, but these small differences appear to impart large trends in the other properties. Better understanding the effects of disorder and group IV alloying in Zn (Sn , Ge) N 2 allows for more accurate modeling of characteristics of this material system for solid state lighting and other applications. [ABSTRACT FROM AUTHOR]

Semilocal density-functional approximations (DFAs), including the state-of-the-art SCAN functional, are plagued by the self-interaction error (SIE). While this error is explicitly defined only for one-electron systems, it has inspired the self-interaction correction method proposed by Perdew and Zunger (PZ-SIC), which has shown promise in mitigating the many-electron SIE. However, the PZ-SIC method is known for its significant numerical instability. In this study, we introduce a novel constraint that facilitates self-consistent localization of the SIC orbitals in the spirit of Edmiston–Ruedenberg orbitals [Rev. Mod. Phys. 35, 457 (1963)]. Our practical implementation within the all-electron numeric atom-centered orbitals code FHI-aims guarantees efficient and stable convergence of the self-consistent PZ-SIC equations for both molecules and solids. We further demonstrate that our PZ-SIC approach effectively mitigates the SIE in the meta-generalized gradient approximation SCAN functional, significantly improving the accuracy for ionization potentials, charge-transfer energies, and bandgaps for a diverse selection of molecules and solids. However, our PZ-SIC method does have its limitations. It cannot improve the already accurate SCAN results for properties such as cohesive energies, lattice constants, and bulk modulus in our test sets. This highlights the need for new-generation DFAs with more comprehensive applicability. [ABSTRACT FROM AUTHOR]

Diffraction-free beams with large depth-of-field have a lot of potential in the field of acoustics, such as imaging, sensing, and particle manipulation. In this study, an acoustic Bessel-like beam is produced using an axicon-sonic crystal lens. The sonic crystal is created using cylindrical glass rods arranged in a triangular shape with a centered square lattice configuration. The numerical simulation between 4 and 8 kHz indicates that the axicon-sonic crystal converts the plane acoustic wave into a Bessel-like beam. The analysis of the beam indicates that the depth of field of this beam depends on the size and periodicity (lattice parameter) of the sonic crystal. The axicon lens also displays variable focal lengths at different frequencies. A graded index layer was implemented to mitigate the reflection caused by the significant impedance mismatch. Experimental validation of acoustic Bessel-like beam formation is also reported for the working frequencies. At 8 kHz, the measured range to the 50 % on-axis intensity was 34 λ , while the focus width at the same frequency was measured to be 2 λ. The integration of three distinct design strategies—axicon shape, sonic crystal, and graded index—expands the possibilities for sound focusing applications. [ABSTRACT FROM AUTHOR]

Epitaxial (Bi, K)TiO3 films with 800- to 900-nm thicknesses were grown hydrothermally at 200 °C on SrTiO3 substrates covered with SrRuO3 layers. Perfectly (001)-oriented films grew on (100)SrTiO3 due to good lattice matching. Films on (110)SrTiO3 had mixed orientations of dominant (110) and minor (101), while three types of (111) orientations with in-plane 120° rotation were observed for the film on (111)SrTiO3. The (101) and (110) orientations of the film deposited on (110)SrTiO3 were tilted by approximately 2.6° and 1.6°, respectively, from surface normal due to the formation of a 90° domain with a twinning plane. The plane-view measurement for the film deposited on (111)SrTiO3 showed nine spots. These are explained by the presence of 15 possible spots resulting from the relaxed 90° domain combination and by overlapping. The lattice parameters of these films explain the tilting angles of these domains. These results reveal the formation of perfectly relaxed 90° domain structures for films grown on (110) and (111)SrTiO3. This differs from our previous data for tetragonal Pb(Zr,Ti)O3 films grown above TC on (110) and (111)SrTiO3 because the present films directly grow the ferroelectric films below TC without phase change. The tilting angle of the polar-axis and the volume fraction of the 90° domain can explain the piezoelectric responses of these films assuming that films have purely an up-state. This suggests that these films show almost pure up-state polarization without 180° domains, at least along surface-normal directions. These data show that these films have domain structures different from the well-known ones for the tetragonal Pb(Zr,Ti)O3 films. [ABSTRACT FROM AUTHOR]

In the process of high temperature service, the mechanical properties of cutting tools decrease sharply due to the peeling of the protective coating. However, the mechanism of such coating failure remains obscure due to the complicated interaction between atomic structure, temperature, and stress. This dynamic evolution nature demands both large system sizes and accurate description on the atomic scale, raising challenges for existing atomic scale calculation methods. Here, we developed a deep neural network (DNN) potential for Ti–N binary systems based on first-principles study datasets to achieve quantum-accurate large-scale atomic simulation. Compared with empirical interatomic potential based on the embedded-atom-method, the developed DNN-potential can accurately predict lattice constants, phonon properties, and mechanical properties under various thermodynamic conditions. Moreover, for the first time, we present the atomic evolution of the fracture behavior of large-scale rocksalt-structure (B1) TiN systems coupled with temperature and stress conditions. Our study validates that interatomic brittle fractures occur when TiN stretches beyond its tensile yield point. Such simulation of coating fracture and cutting behavior based on large-scale atoms can shed new light on understanding the microstructure and mechanical properties of coating tools under extreme operating conditions. [ABSTRACT FROM AUTHOR]

A key development toward new electronic devices integrating memory and processing capabilities could be based on the electric control of the spin texture of charge carriers in semiconductors. In that respect, GeTe has been recently recognized as a promising ferroelectric Rashba semiconductor, with giant spin splitting of the band structure, due to the inversion symmetry breaking arising from ferroelectric polarization. Here, we address the temperature dependence of the ferroelectric structure of GeTe thin films grown on Si(111). We demonstrate the hysteretic behavior of the ferroelectric domain density upon heating/cooling cycles by low energy electron microscopy. This behavior is associated with an abnormal evolution of the GeTe lattice parameter as shown by x-ray diffraction. We explain these thermomechanical phenomena by a large difference of thermal expansion coefficients between the film and the substrate and to the pinning of the GeTe/Si interface. The accumulated elastic energy by the GeTe thin film during sample cooling is released by the formation of a -nanodomains with in-plane ferroelectric polarization components. [ABSTRACT FROM AUTHOR]

Layered electrides are a unique class of materials with anionic electrons bound in interstitial regions between thin, positively charged atomic layers. While density-functional theory is the tool of choice for computational study of electrides, there has to date been no systematic comparison of density functionals or dispersion corrections for their accurate simulation. There has also been no research into the thermomechanical properties of layered electrides, with computational predictions considering only static lattices. In this work, we investigate the thermomechanical properties of five layered electrides using density-functional theory to evaluate the magnitude of thermal effects on their lattice constants and cell volumes. We also assess the accuracy of five popular dispersion corrections with both planewave and numerical atomic orbital calculations. [ABSTRACT FROM AUTHOR]

Strain-related piezoelectric polarization is detrimental to the radiative recombination efficiency for InGaN-based long wavelength micro-LEDs. In this paper, partial strain relaxation of InGaN multiple quantum wells (MQWs) on the wafer scale has been demonstrated by adopting a partially relaxed InGaN superlattice (SL) as the pseudo-substrate. Such a pseudo-substrate was obtained through an electro-chemical etching method, in which a sub-surface InGaN/InGaN superlattice was etched via threading dislocations acting as etching channels. The degree of strain relaxation in MQWs was studied by x-ray reciprocal space mapping, which shows an increase of the in-plane lattice constant with the increase of etching voltage used in fabricating the pseudo-substrate. The reduced strain in the InGaN SL pseudo-substrate was demonstrated to be transferable to InGaN MQWs grown on top of it, and the engineering of the degree of strain relaxation via porosification was achieved. The highest relaxation degree of 44.7% was achieved in the sample with the porous InGaN SL template etched under the highest etching voltage. Morphological and structural properties of partially relaxed InGaN MQWs samples were investigated with the combination of atomic force and transmission electron microscopy. The increased porosity of the InGaN SL template and the newly formed small V-pits during QW growth are suggested as possible origins for the increased strain relaxation of InGaN MQWs. [ABSTRACT FROM AUTHOR]

Rare-earth nickelates (RENiO3: RE≠La) exhibit metal–insulator transition (MIT) properties that enable potential applications, such as critical temperature resistance thermistors, optoelectronic switches, and correlated logical devices. Nevertheless, their abrupt structural distortion across MIT results in mechanical stresses and forms microcracks within the bulk RENiO3, and this irreversibly reduces their resistive change during MIT that further impedes their practical applications. Herein, we demonstrate a compositing strategy that simultaneously improves the MIT performances and mechanical strength of RENiO3 by introducing a secondary phase of perovskite oxides with similar lattice parameters and high resistivity. Despite its much higher resistivity compared to RENiO3 (e.g., RE = Sm or Pr), introducing the LaMnO3 compositing phase under high oxygen pressure surprisingly reduces the matrix resistivity. Furthermore, such a compositing process (e.g., 20% LaMnO3) also effectively improves the mechanical strength of RENiO3 by eight times. Such counterintuitive variations are attributed to the similar structure and lattice parameter between RENiO3 and the perovskite composites that modify the grain boundary. As a result, the resistive change is more abrupt across MIT owing to the reduction in the resistivity associated with the grain boundary, while the defect generation and propagation are also suppressed that improves the mechanical properties. This further pave the way to the application of bulk RENiO3 as discrete devices in correlated electronics. [ABSTRACT FROM AUTHOR]

Lattice simulations are an important class of problems in crystalline solids, surface science, alloys, adsorption, absorption, separation, catalysis, to name a few. We describe a fast computational method for performing lattice thermodynamic calculations that is based on the use of the reverse Monte Carlo (RMC) technique and multiple short-range order (SRO) parameters. The approach is comparable in accuracy to the Metropolis Monte Carlo (MC) method. The equilibrium configuration is determined in 5–10 Newton–Raphson iterations by solving a system of coupled nonlinear algebraic SRO growth rate equations. This makes the RMC-based method computationally more efficient than MC, given that MC typically requires sampling of millions of configurations. The technique is applied to the interacting 2D adsorption problem. Unlike grand canonical MC, RMC is found to be adept at tackling geometric frustration, as it is able to quickly and correctly provide the ordered c(2 × 2) adlayer configuration for Cl adsorbed on a Cu (100) surface. [ABSTRACT FROM AUTHOR]

Gauss chains are one-dimensional nonperiodic lattices in which lattice sites are located at z j = j n d , with j ∈ W , n ∈ N , and d being the underlying lattice constant. They may potentially be realized in semiconductor superlattices or tailored chain molecules. In recent work, we have characterized the electronic delocalized states for the quadratic Gauss chain n = 2 obtained using a one-dimensional transfer-matrix approach applied to the Kronig–Penney model. We here extend those results to cases of larger n , illustrating the approach for n = 3 , 4, and 5. Beginning with the structure factor, we find that the case n = 2 has a visually evident structure lacking for n > --> 2 , and this structure (or lack thereof) is reflected in the statistics of the structure factor. Turning to the electronic structure, the delocalized-state spectrum for each n is singular-continuous with delocalized states at wavevectors k for all rational multiples r s of π d with r , s ∈ N coprime in the limit of weak onsite potential parameter λ. Most states, however, become localized at a state-dependent threshold value of | λ |. The case n = 2 appears to exhibit delocalized-state spectra that most clearly reveal the hidden symmetry of these systems. Gauss chains with various n , therefore, provide a way (in principle) to realize a class of functions of number-theoretic importance. [ABSTRACT FROM AUTHOR]

The Ca-based fluorinated MOF, named UoC-9 (UoC = University of Cologne), was previously published, crystallising in an orthorhombic crystal system with a 2nd order phase transition (Ima2 to Pna21) between room temperature and 100 K. Herein, this MOF was used as a crystalline sponge to embed a selection of six different small guest molecules inside its pores by liquid exchange. After confirming that the guest molecules were successfully loaded into the pores of UoC-9, the resulting host–guest systems were extensively analysed via single crystal X-ray diffraction. The different crystal structures allowed us to investigate the structural behaviour of UoC-9 in response to the embedded guest molecules. The lattice parameters as well as the phase transition are influenced differently by the various guests, which is described in detail by supplementary Hirshfeld surface analyses enabling us to examine the underlying host–guest interactions. The NMP@UoC-9 (NMP = N-methyl-2-pyrrolidone) system exhibits superstructure reflections with a tripled b-axis, which was also elucidated within this work. [ABSTRACT FROM AUTHOR]

The photocatalytic activity of photocatalysts can be enhanced by cation doping, and the dopant concentration plays a key role in achieving high efficiency. This study explores the impact of copper (Cu) doping at concentrations ranging from 0% to 10% on the microstructural, optical, electronic, and photocatalytic properties of zinc oxide (ZnO) nanostructures. The x-ray diffraction analysis shows a non-linear alteration in the lattice parameters with increasing the Cu content and the formation of CuO as a secondary phase at the Cu concentration of >3%. Density functional theory calculations provide insights into the change in the electronic structures of ZnO induced by Cu doping, leading to the formation of localized d electronic levels above the valence band maximum. The modulation of the electronic structure of ZnO by Cu doping facilitates the visible light absorption via O 2p → Cu 3d and Cu 3d → Zn 2p transitions. Photoluminescence spectroscopy reveals a quenching of the defect-related emission peak at approximately 570 nm for all Cu-doped ZnO nanostructures, indicating a reduction in the structural and other defects. The photocatalytic activity tests confirm that the ZnO nanostructures doped with 3% Cu exhibit the highest efficiency compared to other samples due to the suitable band-edge position and visible light absorption. [ABSTRACT FROM AUTHOR]

The location of the H atoms in Ti, Zr, and Hf is crucial to the formation of the hydrides in these metals as it influences the crystal lattice transformation and the hydrogen diffusion involved in the hydride formation process. Although Ti, Zr, and Hf are all of hexagonal close-packed structure with similar lattice parameters, the solute H atom occupies the octahedral interstice in Ti but the tetragonal interstice in Zr and Hf, of which the origin is still mysterious. In the present work, the origin of the distinct site occupation behavior of H atom in Ti and Zr/Hf is investigated through first principles calculations. The calculated solution energies confirm that H prefers the octahedral interstice in Ti but the tetrahedral interstice in Zr and Hf. We ascribe the distinct site occupations of H in Ti and Zr/Hf to the varying Coulomb repulsion between the H (as a screened proton in the metals) and the matrix atoms against the interstitial size. The competition between the H-induced electron accumulation effect and the matrix atom debonding effect might matter as well. We propose that, as a general rule, a H atom prefers the site with a trade-off between a large space and a high electron density in metals. • Hydrogen occupies octahedral interstice in Ti but tetrahedral interstice in Zr/Hf. • H-metal atom Coulomb repulsion is responsible for the distinct site occupation of H. • H-induced electron redistribution might matter to the distinct site occupation of H. • H prefers the site with a trade-off between large space and high electron density. [ABSTRACT FROM AUTHOR]

This paper is dedicated to improving the sintering and conductivity of BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) by adding ZnO–CuO dual-sintering aids. The synergistic effects of liquid-sintering of Zn and B-site substitution of Cu on the sinterability and proton conductivity of BZCYYb are systematically investigated. X-ray diffraction (XRD) analysis of BZCYYb after addition of ZnO–CuO (BZCYYb-Zn-Cu) confirms the complete perovskite phase formation without any secondary phase. The substitution of Ce4+ (0.87 Å) with Zn2+ (0.74 Å) or Cu2+ (0.73 Å) induces a shift in XRD diffraction peak to higher angle due to a decrease in lattice constant. Energy dispersive X-ray spectroscopy analysis indicate a distinct distribution of Zn primarily at the grain boundaries, while Cu is predominantly located within the grains of BZCYYb-Zn-Cu. The addition of ZnO–CuO into BZCYYb results in a denser microstructure with larger average grain size. Furthermore, the substitution of Ce4+ by Cu2+ increases the concentration of oxygen vacancies and reduces activation energy. For BZCYYb-Zn-Cu, the proton conductivity reaches 4.52 × 10−2 S/cm at 750 °C, approximately 3 times higher than that of BZCYYb. This enhancement can be attributed to the synergistic effects of larger average grain size resulting from liquid phase sintering of Zn, low active energy, and high concentration of oxygen vacancies arising from Cu B-site substitution. BZCYYb-Zn-Cu is used as the electrolyte for anode support SOFC, and the single cell exhibits remarkable electrochemical performance and excellent stability in H 2 fuel. This research establishes a crucial theoretical foundation for the preparation and performance evaluation for large-size protonic ceramic cell. • Zn is mainly aggregated at grain boundaries, while Cu is mostly distributed in the grains bulk. • ZnO–CuO synergistically promote the sinterability and conductivity for BZCYYb. • The SOFC with BZCYYb-Zn1-Cu1 electrolyte exhibits high electrochemical performance. [ABSTRACT FROM AUTHOR]

This paper reports an extensive investigation on the structural, dielectric, ferroelectric and pyroelectric properties of 0.7Ba 1-x Sr x TiO 3 – 0.3Bi 0.5 Na 0.5 TiO 3 (x = 0.0, 0.5, 0.6, 0.7) ceramics synthesized via conventional solid-state reaction (SSR) technique. X-ray diffraction data confirms the presence of pure perovskite phase. The variation of lattice parameters with strontium concentration in 0.7Ba 1-x Sr x TiO 3 – 0.3Bi 0.5 Na 0.5 TiO 3 ceramics were evaluated using the Rietveld refinement of the XRD data. The variation of dielectric permittivity with temperature (ε' ∼ T) shows the diffused phase transition and all the parameters related to the relaxor ferroelectrics (relaxation coefficient, activation energy and freezing temperature) were evaluated. The energy storage properties of the as-prepared ceramics were evaluated using the room temperature PE loop. Amongst the as-prepared ceramics, the composition with x = 0.5 possesses the highest energy storage density of 0.46 J/cm3 with an efficiency of 90 %. The temperature dependent P-E loops were used to study the electrocaloric effect (ECE). The ECE calculations were performed using in-direct method based on Maxwell's thermodynamic relations. A maximum adiabatic temperature change of 0.32 K is achieved at 268 K under a small applied electric field of 25 kV/cm for the ceramic with Sr content x = 0.5. Additionally, electrocaloric responsivity ξ max = 0.13 K mm/kV was also found for the studied ceramics. The above results show that the ceramic 0.7Ba 1-x Sr x TiO 3 – 0.3Bi 0.5 Na 0.5 TiO 3 with the composition x = 0.5 is a viable lead-free option for application in solid state refrigeration. [ABSTRACT FROM AUTHOR]

Perovskite oxides have huge potential applications in carbon capture and utilization as oxygen transport membranes (OTM) and solid oxide fuel cell (SOFC) electrodes. SrFeO 3- δ -based perovskite material, as the promising candidate, possesses high mixed ionic-electronic conductivity, but its partial application is impeded by poor stability under CO 2 conditions. In this work, SrFe 0.9 M 0.1 O 3- δ (SFM, M = Fe, Al, Zr, Nb, W) ceramic membranes were synthesized to study the effects of different valence B-site ions doping on the stability and CO 2 adsorption process of perovskite oxides. The phase structure, thermal expansion property, CO 2 tolerance, and CO 2 absorption mechanism on surfaces of SFM were investigated systematically. B-site doping stables the pure cubic structure, improves the high-temperature structural stability, and reduces the thermal expansion coefficient (TEC) by increasing the lattice parameters and metal-oxygen average binging energy (ABE) of SFM. Moreover, density functional theory (DFT) calculations indicate that although B-site ions doping promotes the adsorption of CO 2 on the FeO 2 -terminated, it inhibits CO 2 adsorption on the Sr-O-Sr site after Zr4+, Nb5+, and W6+ doping, causing the reduction of the CO 2 desorption. The results offer new insights for designing perovskite oxides in the carbon neutralization field. • Different valence ions B-site dope SrFeO 3- δ perovskite oxide used in the CCUS. • SrFe 0.9 M 0.1 O 3- δ (SFM, M = Fe, Al, Zr, Nb, W) ceramic membranes are synthesized. • The increase of lattice parameters stabilizes the cubic structure of SFM. • The structure stability at high temperatures is improved by B-site ion doping. • The CO 2 adsorption mechanism on the SFM surfaces is revealed by DFT calculations. [ABSTRACT FROM AUTHOR]

This paper investigated the impact of Co ions doping on the structure, magnetic properties, and magnetocaloric effect for La 0.8 Sr 0.2 Mn 1- x Co x O 3 ceramics (LSMCO) by sol-gel method and first-principles calculations The use of first-principles calculations was provided for subsequent experiments. The sol-gel preparation of LSMCO ceramics and sintered at 950 °C for 10 h. It was shown that the samples' cell volume and lattice constants changed slightly with increasing Co2+ doping but remained a rhombohedral structure (No.167, R-3c space group) by statistics of TEM and XRD. The average particle size for the LSMCO ceramics ranged from 130 nm to 170 nm. LSMCO's chemical composition was verified by EDS and XPS and it was demonstrated that Co2+ was successfully doped. The oxidation state of La was found to be +3, Mn is a mixture of Mn3+ and Mn4+ valence states, and Co is a mixture of Co3+ and Co2+ valence states using XPS. In the vicinity of Tc, all samples presented the second-order magnetic phase transition from ferromagnetic to paramagnetic resorting to normalization and the Banerjee criterion. The Tc dropped from 292 K to 237 K with increasing Co2+ doping. The blocking temperature and the saturation magnetization were suppressed by the Co2+ substitution while the maximum magnetic entropy change of the LSMCO ceramics was observed to reduce as Co2+ increased. When the external magnetic field is 5 T, the La 0.8 Sr 0.2 Mn 0.95 Co 0.05 O 3 ceramics has a Tc of 292 K and a maximum magnetic entropy change value of 3.47 J/(kg K). [ABSTRACT FROM AUTHOR]

This study explores a novel method for fabricating Ca-α-sialon ceramics using a calcium aluminate oxide eutectic additive. Conventional sintering techniques for Ca-α-sialon ceramics employ nitrogen-containing additives to facilitate the Si–N bond substitution mechanism with Al–O and Al–N bonds. In this work, calcium aluminate additives are utilized, leading to the formation of Ca-α-sialon ceramics via carbothermal reduction processes and partial nitridation of aluminum oxide. The influence of varying calcium aluminate content (5, 10, 15, 30, and 40 wt%) on the phase composition of Ca-α-sialon ceramics, produced by hot pressing at 1650 °C in a nitrogen atmosphere, was investigated. Results indicate that increasing the calcium aluminate content leads to the formation of a β-sialon phase, which subsequently transforms into Ca-α-sialon. At 40 wt% calcium aluminate, complete conversion of α-Si 3 N 4 to Ca-α-sialon is achieved, with significant glassy phase formation at the grain boundaries. The study elucidates the relationship between calcium aluminate content, phase composition, lattice parameters, mechanical properties, oxidation resistance, and thermal expansion of the ceramics. [ABSTRACT FROM AUTHOR]

Ceramics of Li 2 Mg 2 GaTi 2 O 8 F (LMGTOF) were prepared by the traditional solid-state method. XRD and TEM results confirmed that a single phase of Li 2 Mg 2 GaTi 2 O 8 F, with an Fd-3m space group and a cubic spinel structure, was formed by the ceramics. It was shown by the results that the lattice parameters of the ceramics at 1050 °C were measured as a = b = c = 8.36576 Å, with a volume of V = 585.485549 Å3. Furthermore, it was observed through the analysis of the Raman peak at 718 cm−1 that an inverse relationship was exhibited between the Raman shift and ε r. Similarly, an opposing trend was also demonstrated between the Q × f value and FWHM. By bond valence analysis, it was shown that Mg2+, Ga3+, and Ti4+ ions were in a "rattling" state, and the large positive deviation between ε corr and ε theo was attributed to the strong "rattling" effect induced by the cations. At 1050 °C, the best microwave dielectric properties (ε r = 14.58, Q × f = 76,689 GHz, and τ f = −52 ppm/°C) were exhibited by LMGTOF ceramics. [ABSTRACT FROM AUTHOR]

The (Al 1-x Cr x) 2 O 3 solid solution (ACS) is expected to be an low pollution chromium source for high-performance alumina-chromium oxide refractory materials. In this work, the effects of Cr 2 O 3 content and reaction conditions on the solid solution behavior in the Al 2 O 3 -Cr 2 O 3 system were explored and the mechanism was revealed. The relationship between the lattice parameters of the formed ACS phase and the content of Cr 2 O 3 was closer to a linear one as the temperature rose, serving as an indicator for a higher degree of reaction. The solid solution reaction between Al 2 O 3 and Cr 2 O 3 was governed by the diffusion processes of Al3+ and Cr3+ at 1300–1500 °C and 1200 °C, respectively, and thus the increase of Cr 2 O 3 content slowed the solid solution reaction at a low temperature whereas promoted it at elevated temperatures. The diffusion process of solid solution reaction within the Al 2 O 3 -Cr 2 O 3 system was consistent with the Cater model; The diffusion activation energy (E a) decreased as the content of Cr 2 O 3 increased at 1300–1500 °C. When the content of Cr 2 O 3 increased from 25 to 60 mol%, the diffusion activation energy decreased from 92.48 to 86.49 kJ/mol−1, which was attributed to the augmentation in the diffusion rate of Cr3+ caused by the increase of Cr 2 O 3 content and its vapor-phase transport mechanism at high temperatures. [ABSTRACT FROM AUTHOR]

The coalescence of nanocrystals that occurs during low-temperature thermal treatments during the purification of hydroxyapatite from pigs has not yet been studied in the context of low-temperature environmentally friendly purification. To preserve the nature of hydroxyapatite, two extraction methods were investigated: Route 1 (autoclave and Soxhlet) and Route 2 (calcination at low temperatures with different times). The focus is on observing the effectiveness of removing fats and proteins while maintaining crystallite size and morphology. DSC showed that coalescence of crystallites occurred at 452, 566, 648, and 704 °C. Raw has a higher IR FWHM (phosphate band) due to the organic material; R1 had a lower FWHM (partial removal of lipids and proteins). Increasing the calcination temperature decreases the FWHM, indicating a shift in vibrational states from surface to bulk, leading to an increase in apparent crystallite size due to coalescence. For 20–80 h at quasi-stable temperatures of 400 and 500 °C, no significant changes occur in the IR spectrum. X-ray diffraction indicates the removal of organic material during calcination, as the peaks become clearer with increasing temperature. The crystallite size is not affected and remains in similar ranges. Purification with hydroxide shows an increase in both lattice parameters, in addition to the fluctuations that occur due to the ionic substitutions that naturally occur in biogenic HAp. And the TEM study confirms that the changes in apparent size from 2D to 3D are the result of the phenomenon of interplanar coalescence at low temperatures that occurs in sintering processes. [ABSTRACT FROM AUTHOR]

β‐Ga2O3 is an emerging ultra‐wide bandgap semiconductor with great promise for power electronics and optoelectronics. Alloys in the In2O3‐Ga2O3 system are interesting for optoelectronic applications, particularly where bandgap tuning is desirable. Herein, β‐(InxGa1–x)2O3 alloys with target compositions x = 0.025 or 0.10 are grown from the melt using the Czochralski and vertical gradient freeze techniques. Growth with 10 mol% In yields only small, needle‐like crystals, while 2.5 mol% In allows growth of centimeter‐sized single crystals. A substantial degree of indium segregation is unveiled by spatial measurements of lattice parameters and the bandgap. The bandgap decreases by a maximum of 0.28 eV in the case of the highest In content crystals. Z‐contrast transmission electron microscopy confirms a solely octahedral coordination of In in the β‐Ga2O3 lattice. With indium concentrations higher than 2.5 mol%, samples contain micron‐scale voids that impart a dark coloration. All measured crystals are electrically conductive, with carrier concentrations varying 1016–1017 cm−3 depending upon the location of the sample in the growth. Lastly, a unique luminescence with unknown origin centered around 2.0 eV is revealed by photoluminescence spectroscopy. [ABSTRACT FROM AUTHOR]

Ammonium‐calcium mixed‐cation pentaborate NH4Ca[B5O7(OH)4]·H2O has been synthesized for the first time. Single‐crystal X‐ray diffraction analysis reveals that it crystallizes in the triclinic space group P‐1 with lattice parameters a = 6.7042(3) Å, b = 7.1859(3) Å, c = 10.7447(4) Å, α = 100.304(3), β = 97.774(3), γ = 96.972(3). The structure is characterized by 1D boron–oxygen chains composed of [B5O7(OH)4]3− polyanions that are further interspaced by Ca2+, NH4+ cations, along with lattice water molecules. The phase purity and thermal stability of the as‐synthesized sample were confirmed by XPRD and TG‐DSC analyses. Experimental UV–vis diffuse reflectance spectroscopy coupled with Urbach fitting indicates a direct bandgap of 4.50 eV, contrasting with theoretical calculations that suggest an indirect bandgap of 5.53 eV. Additionally, both theoretical computation and polarized light experimental test indicate that NH4Ca[B5O7(OH)4]·H2O exhibits moderate birefringence. [ABSTRACT FROM AUTHOR]