Pressure-Induced Anion Order–Disorder Transition in Layered Perovskite Sr₂LiHOCl₂

Abstract

While cation order–disorder transitions have been extensively investigated because of their decisive impact on chemical and physical properties, only few anion order–disorder transitions are known. Here, we show that Sr2CuO2Cl2-type layered perovskite Sr2LiHOCl2 exhibits a pressure-induced H–/O2– order–disorder transition. When synthesized at ambient and low pressures (≤2 GPa), Sr2LiHOCl2 is isostructural to orthorhombic Eu2LiHOCl2 (Cmcm) with a H–/O2– order at the equatorial sites. However, applying a higher pressure (5 GPa) during synthesis causes the equatorial anions to be disordered, leading to a tetragonal symmetry (I4/mmm) with a loss of the superstructure. The structural analysis revealed that, in the ambient pressure phase, HLi2Sr4 and OLi2Sr4 octahedra have distinct sizes to stabilize otherwise underbonded oxide ions, which is less important at the higher pressure. Anion-disordered Sr2LiHOBr2 and Ba2LiHOCl2 were also obtained at 5 GPa. Given the abundant layer-type anion order in perovskite-based oxyhydrides (e.g., La2LiHO3), the inclusion of additional anions (e.g., chloride) expands the frontiers of anion ordering patterns and their distribution control with the benefit of improving ionic conduction in solids.

Combining Nitridoborates, Nitrides and Hydrides—Synthesis and Characterization of the Multianionic Sr6N[BN2]2H3

“…Starting with Ca 2 BN 2 H in 2004, this class combines highly stable nitridoborate ions next to the elusive hydride ions within one material [25–26] . When it comes to multinary compounds with three or more different anions, the hydride family is only sparsely explored yet, with SmH 0.78 OF 0.22 and Sr 2 LiHOCl 2 being just two recent members [27–28] . Due to the high reactivity and omnipresent abundance of oxygen, this class exclusively consists of hydride oxides.…”

“…[25][26] When it comes to multinary compounds with three or more different anions, the hydride family is only sparsely explored yet, with SmH 0.78 OF 0.22 and Sr 2 LiHOCl 2 being just two recent members. [27][28] Due to the high reactivity and omnipresent abundance of oxygen, this class exclusively consists of hydride oxides. Neither an oxide-free nor a complex anion containing compound was found to date with such a multianionic composition.…”