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The structural, elastic, and electronic properties of orthorhombic Cd2SiO4 and Hg2GeO4 were examined under varying pressure conditions using first-principles calculations based on density functional theory employing the Projector Augmented Wave method. The obtained cell parameters at 0 GPa were found to align well with existing experimental data. We delved into the pressure dependence of normalized lattice parameters and elastic constants. In Cd2SiO4, all lattice constants decreased as pressure increased, whereas, in Hg2GeO4, parameters a and b decreased while parameter c increased under pressure. Employing the Hill average method, we calculated the elastic moduli and Poisson's ratio up to 10 GPa, noting an increase with pressure. Evaluation of ductility/brittleness under pressure indicated both compounds remained ductile throughout. We also estimated elastic anisotropy and Debye temperature under varying pressures. Cd2SiO4 and Hg2GeO4 were identified as indirect band gap insulators, with estimated band gaps of 3.34 eV and 2.09 eV, respectively. Interestingly, Cd2SiO4 exhibited a significant increase in band gap with increasing pressure, whereas the band gap of Hg2GeO4 decreased under pressure, revealing distinct structural and electronic responses despite their similar structures. [ABSTRACT FROM AUTHOR]

Two novel oxides with Pb2Rh2O7 and Y2Rh2O7 compositions were synthesised using high pressure, high temperature techniques at 19 GPa and 8 GPa, respectively. Structurally, both compounds were determined to crystallise in the cubic pyrochlore structure, space group Fd3¯m, with no observed oxygen vacancies. Both oxides have effectively identical Rh–O bond lengths of 1.987 Å and a bond-valence sum (BVS) of 4.2 that confirm a Rh4+ oxidation state. Physical property measurements for Pb2Rh2O7 are consistent with a metallic ground state. This is similar to other Pb2M2O7 oxides where M = Ru, Ir, and Os. Y2Rh2O7 represents an unusual case of the lower density (6.356 g cm−3) pyrochlore structure being stabilised under high pressure conditions, while the analogous, higher density (7.031 g cm−3) perovskite YRhO3 is stabilised by synthesis under ambient pressure conditions. The Rh4+ state results in a S = ½ magnetic ground state. Magnetisation measurements suggest strong AFM coupling in Y2Rh2O7. However, long range AFM order is not observed down to 2 K presumably due to the geometric frustration of the pyrochlore lattice. Specific heat and resistivity measurements indicate a large electronic contribution to the heat capacity. The Wilson ratio of 4.78(11) is well above 2, indicating nearness to magnetism and the likely presence of Rh moments in the background of the conduction electrons. Catalytic activity indicated a greater correlation with other Rh pyrochlores as opposed to dependence on the Rh oxidation state. [ABSTRACT FROM AUTHOR]

Organic polar crystals are a promising material platform for achieving unique nonlinear nanophotonic properties. Mainly, tunable second‐harmonic generation (SHG) with continuous‐wave (CW) pump sources is considered as breakthrough technology for optical switching, actuation, sensing, chip‐integrated coherent light sources, and low‐threshold tunable microlasers. Here, the discovery of tunable CW SHG in a polar (non‐centrosymmetric) electro‐mechanical microcrystal cavity of 4‐(4‐(methylthio)phenyl)‐2,6‐di(1H‐pyrazol‐1‐yl)pyridine (UOH1) is demonstrated. As a result of total internal reflection in mirror‐like light‐reflecting facets and its high second‐order nonlinear susceptibility, the octahedron‐shaped cavities exhibit both bright femtosecond and CW‐pumped SHG with coherent whispering gallery mode (WGM) and bow‐tie‐like (BT) optical modes excited in its spectrum. Moreover, for an external dc electric field of about 23 kV cm−1 the microcavity displays 0.18 nm resonant wavelength peak shift in the second harmonic signal due to electrostriction (strain effect). [ABSTRACT FROM AUTHOR]

To build a safe, sustainable, and reliable disposal system for radioactive waste from the nuclear industry, researchers need to understand the physical and chemical aspects of technetium (Tc)‐based oxides. Here, structure–property correlation studies of scheelite‐type AgTcO4 are performed using ab initio calculations. The full phonon dispersion studies reveal the dynamical stability of this compound. The partial phonon density of states, including the complete mode assignment of the vibrational frequencies, shows the maximum involvement of silver (Ag) atoms in the low‐frequency range, while high contribution of oxygen atoms and average contribution from Tc atoms are found throughout the frequency region. The electronic band structure shows that the main contribution to the bottom of the conduction band is Tc d states with a minor contribution from oxygen p states, while the top of the valence band is from Ag d states, which are responsible for the electronic transitions. The frequency‐dependent dielectric functions and computed optical properties show near‐isotropy behavior and, together with absorption peak in the low‐energy range, indicate that AgTcO4 may be a good phosphor when doped with a suitable activator. The estimations are grounded by the available experimental data and also deliver direction for distinct and futuristic applications of AgTcO4. [ABSTRACT FROM AUTHOR]

This article presents a thorough density functional theory based comparative study on nitrogen‐rich 5‐aminotetrazole alkali metal salts M 5‐At (M = Li, K, Rb, Cs). The calculated structural parameters using plane‐wave pseudopotential method are consistent with the experimental results. The computed vibrational frequencies at ambient pressure show that vibrational modes in high energy region are due the NH bond of NH2 group. Pressure variation IR spectra of these materials show clear frequency shifts where Li 5‐At shows an overall red shift below 900 cm−1 contrary to the blue shift seen in other materials in this range. The born effective charge values reveal the presence of strong covalency between N, H, and C atoms whereas an increased ionic nature is seen as the atomic number of metal atoms increases. Furthermore, we used full potential linear augmented plane wave (FP‐LAPW) method for calculating electronic structure and optical properties with TB‐mBJ potential which provides an enhanced band gap for all materials compared to standard GGA functional. Electronic structure calculation reveals that all the compounds are indirect band gap insulators with the exception of Li 5‐At. The computed partial density of states show mixed ionic‐covalent nature in metal‐N/C bonds and covalent nature in NC bonds. In addition, we are also presenting the optical properties such as real and imaginary dielectric constant, absorption, refraction, reflection, loss spectrum as functions of photon energy. From the optical properties we can conclude that all the studied compounds are optically anisotropic in nature and are good absorbers in the ultraviolet (UV) region. [ABSTRACT FROM AUTHOR]

To build a safe, sustainable, and reliable disposal system for radioactive waste from the nuclear industry, researchers need to understand the physical and chemical aspects of technetium (Tc)‐based oxides. Here, structure–property correlation studies of scheelite‐type AgTcO4 are performed using ab initio calculations. The full phonon dispersion studies reveal the dynamical stability of this compound. The partial phonon density of states, including the complete mode assignment of the vibrational frequencies, shows the maximum involvement of silver (Ag) atoms in the low‐frequency range, while high contribution of oxygen atoms and average contribution from Tc atoms are found throughout the frequency region. The electronic band structure shows that the main contribution to the bottom of the conduction band is Tc d states with a minor contribution from oxygen p states, while the top of the valence band is from Ag d states, which are responsible for the electronic transitions. The frequency‐dependent dielectric functions and computed optical properties show near‐isotropy behavior and, together with absorption peak in the low‐energy range, indicate that AgTcO4 may be a good phosphor when doped with a suitable activator. The estimations are grounded by the available experimental data and also deliver direction for distinct and futuristic applications of AgTcO4. [ABSTRACT FROM AUTHOR]

Beryllium silicate, recognized as the mineral phenakite (Be 2 SiO 4 ), is a prevalent constituent in Earth's upper mantle. This study employs density-functional theory (DFT) calculations to explore the structural, mechanical, dynamical, thermodynamic, and electronic characteristics of this compound under both ambient and high-pressure conditions. Under ideal conditions, the DFT calculations align closely with experimental findings, confirming the mechanical and dynamical stability of the crystalline structure. Phenakite is characterized as an indirect band gap insulator, possessing an estimated band gap of 7.83 eV. Remarkably, oxygen states make a substantial contribution to both the upper limit of the valence band and the lower limit of the conduction band. We delved into the thermodynamic properties of the compound, including coefficients of thermal expansion, free energy, entropy, heat capacity, and the Gruneisen parameter across different temperatures. Our findings suggest that Be 2 SiO 4 displays an isotropic behavior based on estimated anisotropic factors. Interestingly, our investigation revealed that, under pressure, the compression of phenakite is not significantly affected by bond angle bending., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Within the burgeoning field of electronic materials, B-N Lewis acid-base pairs, distinguished by their partial charge distribution across boron and nitrogen centers, represent an underexplored class with significant potential. These materials exhibit inherent dipoles and are excellent candidates for ferroelectricity. However, the challenge lies in achieving the optimal combination of hard-soft acid-base pairs to yield B-N adducts with stable dipoles. Herein, we present an enantiomeric pair of B-N adducts [ R/S C 6 H 5 CH(CH 3 )NH 2 BF 3 ] ( R/S MBA-BF 3 ) crystallizing in the polar monoclinic P2 1 space group. The ferroelectric measurements on R MBA-BF 3 gave a rectangular P-E hysteresis loop with a remnant polarization of 7.65 μC cm -2 , a value that aligns with the polarization derived from the extensive density-functional theory computations. The PFM studies on the drop-casted film of R MBA-BF 3 further corroborate the existence of ferroelectric domains, displaying characteristic amplitude-bias butterfly and phase-bias hysteresis loops. The piezoelectric nature of the R MBA-BF 3 was confirmed by its direct piezoelectric coefficient (d 33 ) value of 3.5 pC N -1 for its pellet. The piezoelectric energy harvesting applications on the sandwich devices fabricated from the as-made crystals of R MBA-BF 3 gave an open circuit voltage (V PP ) of 6.2 V. This work thus underscores the untapped potential of B-N adducts in the field of piezoelectric energy harvesting., (© 2024 Wiley‐VCH GmbH.)

We report an extensive study of the optical and structural properties of NiWO 4 combining experiments and density functional theory calculations. We have obtained accurate information on the pressure effect on the crystal structure determining the equation of state and compressibility tensor. We have also determined the pressure dependence of the band gap finding that it decreases under compression because of the contribution of Ni 3 d states to the top of the valence band. We report on the sub-band-gap optical spectrum of NiWO 4 showing that the five bands observed at 0.95, 1.48, 1.70, 2.40, and 2.70 eV correspond to crystal-field transitions within the 3 d 8 ( t 2g 6 e g 2 ) configuration of Ni 2+ . Their assignment, which remained controversial until now, has been resolved mainly by their pressure shifts. In addition to the transition energies, their pressure derivatives are different in each band, allowing a clear band assignment. To conclude, we report resistivity and Hall-effect measurements showing that NiWO 4 is a p -type semiconductor with a resistivity that decreases as pressure increases., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Isolation and structural characterization of novel organoantimony(V)-based oxo clusters are reported. (RSb) 4 (OH) 4 ( t -BuPO 3 ) 6 and (RSb) 2 (O)( t -BuPO 3 H) 6 independently in the presence of pyridine under solvothermal conditions afford the hexanuclear organoantimonate clusters [(RSb) 6 (μ 3 -O) 2 (μ 2 -O) 6 ( t -BuPO 3 ) 4 ], where R = p - i -PrC 6 H 4 ( 1 ), p -ClC 6 H 4 ( 2 ). Further, reaction of organostibonate phosphonate with Ti(O i Pr) 4 in the presence of pyridine under solvothermal conditions afforded the mixed-metal titanium stibonate hexanuclear clusters [(RSb) 2 Ti 4 (μ 3 -O) 2 (μ 2 -O) 2 ( t -BuPO 3 ) 4 (μ-OCH 3 ) 4 (OCH 3 ) 4 ], where R = p - i -PrC 6 H 4 ( 3 ), p -ClC 6 H 4 ( 4 ). Band gap measurements were performed on 1 - 4 . They reveal a remarkable reduction in the band gap on moving from the heavier main-group-based oxo cages ( 1 and 2 ) to the titanium-incorporated oxo cages ( 3 and 4 ).