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

Abstract

We present a detailed experimental and computational investigation of the influence of pressure on the mixed-anion oxyhydride phase Ba 2 YHO 3 , 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 Ba 2 ScHO 3 . Density functional theory (DFT) calculations reveal that the application of pressure drives two sequential B 1– B 2 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.

Electron Counting and High-Pressure Phase Transformations in Metal Hexaborides

“…A phase transition is predicted to occur wherever the calculated enthalpy change between two phases, Δ H = Δ E + P Δ V , equals zero. The approximation of neglecting the vibrational entropy contribution to the free energy provides good agreement with experimentally measured transition pressures for ionic solids. − For CaB 6 , a Pm 3̅ m -to- Cmcm transition is predicted at 15 GPa and a Cmcm -to- I 4/ mmm transition is predicted at 35 GPa, and for SrB 6 , the same transitions occur at 44 and 62 GPa, respectively. The CaB 6 results agree closely with those of Kolmogorov et al, who predicted the same transitions at 13 and 32 GPa, respectively.…”

Electron counting and high pressure phase transformations in metal hexaborides

“…The approximation of neglecting the vibrational entropy contribution to the free energy provides good agreement with experimentally measured transition pressures for ionic solids. [35][36][37] For CaB 6 a P m 3m-to-Cmcm transition is predicted at 15 GPa and a Cmcm-to-I4/mmm transition is predicted at 35 GPa, and for SrB 6 the same transitions occur at 44 GPa and 62 GPa respectively. The CaB 6 results agree closely with those of Kolmogorov et al, 25 who predicted the same transitions at 13 and 32 GPa respectively.…”

Compressibility Studies of Copper Selenides Obtained by Cation Exchange Reaction Revealing the New CsCl Phase

“…After 9 GPa, the CsCl-type lattice is preserved in the NCs up to 40 GPa (Figure 2b). Pressure-induced phase transition to CsCl-type phase has been observed typically in oxides 49 and has been partially attributed to repulsion between anions resisting the structural compressive changes in the anionrich layers 50 .…”