Structure Evolution of Ge-Doped CaTiO (CTG) at High Pressure: Search for the First 2:4 Locked-Tilt Perovskite by Synchrotron X-ray Diffraction and DFT Calculations.

This research investigates the high-pressure behavior of the Ca(TiGe)O perovskite, a candidate of the locked-tilt perovskite family (orthorhombic compounds characterized by the absence of changes in the octahedral tilt and volume reduction under pressure controlled solely by isotropic compression). The study combines experimental high-pressure synchrotron diffraction data with density functional theory (DFT) calculations, complemented by the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), to understand the structural evolution of the perovskite under pressure. The results show that CTG undergoes nearly isotropic compression with the same compressibility along all three unit-cell axes (i.

MgAlSiO jeffbenite inclusion in super-deep diamonds is thermodynamically stable at very shallow Earth's depths.

Jeffbenite (having the same chemical composition of pyrope, ~ MgAlSiO, and also known as TAPP phase) is a mineral inclusion only found in diamonds formed between about 300 and 1000 km depth) and is considered a stable phase in the transition zone (410-660 km depth) and/or in the shallowest regions of the lower mantle (around 660-700 km depth). This rare and enigmatic mineral is considered to be a pressure marker for super-deep diamonds and therefore it has a key role in super-deep diamond research. However, the pressure-temperature stability fields for MgAlSiO jeffbenite is unknown and its actual formation conditions remain unexplored.

Ab Initio Thermodynamic and Thermophysical Properties of Sodium Metasilicate, NaSiO, and Their Electron-Density and Electron-Pair-Density Counterparts.

Thermodynamic and thermophysical properties of NaSiO in the Cmc2 structural state are computed ab initio using the hybrid B3LYP density functional method. The static properties at the athermal limit are first evaluated through a symmetry-preserving relaxation procedure. The thermodynamic properties that depend on vibrational frequencies, viz.