Equations of state of alkali hydrides at high pressures

Structural diversity and hydrogen storage properties in the system K-Si-H

KSiH₃ exhibits 4.1 wt% experimental hydrogen storage capacity and shows reversibility under moderate conditions, which provides fresh impetus to the search for other complex hydrides in the K-Si-H system. Here, we reproduce the stable Fm3̄m phase of K₂SiH₆ and uncover two denser phases, space groups P3̄m1 and P6₃mc at ambient pressure, by means of first-principles structure searches. We note that P3̄m1-K₂SiH₆ has a high hydrogen content of 5.4 wt% and a volumetric density of 88.3 g L^-1. Further calculations suggest a favorable dehydrogenation temperature T_des of -20.1/55.8 °C with decomposition into KSi + K + H₂. The higher hydrogen density and appropriate dehydrogenation temperature indicate that K₂SiH₆ is a promising hydrogen storage material, and our results provide helpful and clear guidance for further experimental studies. We found three further potential hydrogen storage materials stable at high pressure: K₂SiH₈, KSiH₇ and KSiH₈. These results suggest the need for further investigations into hydrogen storage materials among such ternary hydrides at high pressure.

Sequential Pressure-Induced B1-B2 Transitions in the Anion-Ordered Oxyhydride Ba2YHO3

We present a detailed experimental and computational investigation of the influence of pressure on the mixed-anion oxyhydride phase Ba₂YHO₃, which has recently been shown to support hydride conductivity. The unique feature of this layered perovskite is that the oxide and hydride anions are segregated into distinct regions of the unit cell, in contrast to the disordered arrangement in closely related Ba₂ScHO₃. Density functional theory (DFT) calculations reveal that the application of pressure drives two sequential B1–B2 transitions in the interlayer regions from rock salt to CsCl-type ordering, one in the hydride-rich layer at approximately 10 GPa and another in the oxide-rich layer at 35–40 GPa. To verify the theoretical predictions, we experimentally observe the structural transition at 10 GPa using high-pressure X-ray diffraction (XRD), but the details of the structure cannot be solved due to peak broadening of the XRD patterns. We use DFT to explore the structural impact of pressure on the atomic scale and show how the pressure-dependent properties can be understood in terms of simple electrostatic engineering.

We investigate a sequence of pressure-induced phase transitions in Ba₂YHO₃, a perovskite oxyhydride with a unique layered anion ordering. Density functional theory and X-ray diffraction together provide a detailed and informative picture of the changes to the crystal structure across the pressure range. This work provides new insights into nonuniform structural flexibility in 2D materials, which can aid targeted materials design in other chemical systems.