Structure and properties of complex hydride perovskite materials

Abstract

Perovskite materials host an incredible variety of functionalities. Although the lightest element, hydrogen, is rarely encountered in oxide perovskite lattices, it was recently observed as the hydride anion H À , substituting for the oxide anion in BaTiO 3 . Here we present a series of 30 new complex hydride perovskite-type materials, based on the non-spherical tetrahydroborate anion BH 4 À and new synthesis protocols involving rare-earth elements. Photophysical, electronic and hydrogen storage properties are discussed, along with counterintuitive trends in structural behaviour. The electronic structure is investigated theoretically with density functional theory solid-state calculations. BH 4 -specific anion dynamics are introduced to perovskites, mediating mechanisms that freeze lattice instabilities and generate supercells of up to 16 Â the unit cell volume in AB(BH 4 ) 3 . In this view, homopolar hydridic di-hydrogen contacts arise as a potential tool with which to tailor crystal symmetries, thus merging concepts of molecular chemistry with ceramic-like host lattices. Furthermore, anion mixing BH 4 À 2X À (X À ¼ Cl À , Br À , I À ) provides a link to the known ABX 3 halides.

Complex and liquid hydrides for energy storage

“…- [85]. Structural dynamics on the anion site are systematically introduced to the perovskite structure type, and anion substitution, where BH 4 -is partially replaced by the heavier halides, Cl -, Br -or I -, readily occurs, contributing to a vast structural flexibility and compositional diversity.…”

Hydrogen Sorption in Erbium Borohydride Composite Mixtures with LiBH4 and/or LiH

“…Li-containing RE borohydrides are also considered as solid state electrolytes for new battery applications, due to their high Li-ion conductivities [20][21][22][23]. RE borohydrides have shown novel properties such as luminescence, and a magnetocaloric effect has also been recently published [24][25][26].…”

Increasing Hydrogen Density with the Cation-Anion Pair BH4−-NH4+ in Perovskite-Type NH4Ca(BH4)3

“…Semi-empirical chemical concepts combining the stabilities of the less stable and more stable borohydrides [2], for instance, have given way to more profound concepts that exploit different kinds of weak interaction [3]. Recently, we reported on a large family of mixed-metal borohydrides crystallizing in the perovskite structure type, the latter being a prime example of functional materials design [4]. As a very stable structure type, the perovskite form allows one to study the behavior of a large range of different metals in a borohydride environment, but also to apply an immense toolbox developed throughout decades of metal-oxide perovskite design.…”

“…A logical further step is to explore anion-mixing on the ligand site. It was shown that the borohydride perovskite host readily takes up halide anions on the borohydride site [4]. In this context, it comes to mind to test the nitrogen-based hydrogen molecules, which are currently being vigorously investigated as means to tailor hydrogen release temperatures [3].…”