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Silver iodo-bismuthates show promise for optoelectronic and other applications. Within this family of materials, AgBiI 4 is a prominent model compound. The complexity of AgBiI 4 has prevented a conclusive determination of specific atomic arrangements of metal atoms in the bulk material. Here, we employ high through-put density functional and novel machine learning methods to determine physically relevant unit cell configurations. We also calculate the fundamental properties of the bulk material using newly discovered configurations. Our results for the lattice constant (12.7 Å) and bandgap (1.8 eV) agree with the previous theory and experiment. We report new predictions for the bulk modulus (7.5 GPa) and the temperature-dependent conductivity mass for electrons ([Formula: see text] at T = 300 K) and holes (7[Formula: see text] at T = 300 K); these masses will be useful in AgBiI 4 -based device simulations. 

Abstract As a unique nonlinear optical material, Ba₃(ZnB₅O₁₀)PO₄(BZBP) boasts a range of distinctive properties, including low anisotropic thermal expansivity, high specific heat, minimal walk‐off effect, large acceptance angle, non‐hygroscopicity, and high conversion efficiency. These features position BZBP as a highly promising candidate for crucial components in ultraviolet (UV) laser systems. Notably, all previous studies have been conducted under ambient pressures. In this research, synchrotron X‐ray diffraction and Raman spectroscopy are employed to investigate BZBP's behavior under extreme conditions. The findings revealed that BZBP remains exceptionally stable up to 43 Gigapascals (GPa), significantly extending its application range from ambient to high‐pressure environments. This stability enhancement opens new avenues for utilizing BZBP in optical systems designed to function under extreme conditions. Additionally, the study determined BZBP's bulk modulus (110 GPa) and linear compressibility along each lattice axis. Theoretical computations are used to assign the Raman modes, characterize their corresponding lattice vibrations, validate the experimental results, and elucidate the mechanisms underlying the material's remarkable stability. 

Rocksalt structure nitrides emerge as a promising class of semiconductors for high-temperature thermoelectric and plasmonic applications. Controlling the bandgap and strain is essential for the development of a wide variety of electronic devices. Here we use (Ti 0.5 Mg 0.5 ) 1−x Al x N as a model system to explore and demonstrate the tunability of both the bandgap and the strain state in rocksalt structure nitrides, employing a combined experimental and computational approach. (Ti 0.5 Mg 0.5 ) 1−x Al x N layers with x ≤ 0.44 deposited on MgO(001) substrates by reactive co-sputtering at 700 °C are epitaxial single crystals with a solid-solution B1 rocksalt structure. The lattice mismatch with the substrate decreases with increasing x , leading to a transition in the strain-state from partially relaxed (74% and 38% for x = 0 and 0.09) to fully strained for x ≥ 0.22. First-principles calculations employing 64-atom Special Quasirandom Structures (SQS) indicate that the lattice constant decreases linearly with x according to a = (4.308 − 0.234 x ) Å for 0 ≤ x ≤ 1. In contrast, the measured relaxed lattice parameter a o = (4.269 − 0.131 x ) Å is linear only for x ≤ 0.33, its composition dependence is less pronounced, and x > 0.44 leads to the nucleation of secondary phases. The fundamental (indirect) bandgap predicted using the same SQS supercells and the HSE06 functional increases from 1.0 to 2.6 eV for x = 0–0.75. In contrast, the onset of the measured optical absorption due to interband transitions increases only from 2.3 to 2.6 eV for x = 0–0.44, suggesting that the addition of Al in the solid solution relaxes the electron momentum conservation and causes a shift from direct to indirect gap transitions. The resistivity increases from 9.0 to 708 μΩ m at 77 K and from 6.8 to 89 μΩ m at 295 K with increasing x = 0–0.44, indicating an increasing carrier localization associated with a randomization of cation site occupation and the increasing bandgap which also causes a 33% reduction in the optical carrier concentration. The overall results demonstrate bandgap and strain engineering in rocksalt nitride semiconductors and show that, in contrast to conventional covalent semiconductors, the random cation site occupation strongly affects optical transitions.