Résumé
Oxide synthesis traces its roots back to BC. Their chemical and physical properties are largely dependent on cation selection. However, the 21st century has witnessed a surge in interest towards compounds composed of multiple anion species, called mixed-anion compounds [1]. In this seminar, recent research trends in mixed anion compounds will be reviewed from the viewpoints of synthesis, structure, and physical properties, with a particular focus on strain engineering – a pivotal concept applied to mixed anion compounds [2-6].
For example, H-anion conduction in BaH2 experiences a drastic reduction due to a phase transition to a low-symmetry phase at low temperatures, but through layer ordering (i.e., Ba2H3X (X = Cl, Br, I)), the halide layer acts as a protective layer, preventing symmetry lowering and allowing excellent H-anion conduction at low temperatures [2]. Medium-temperature nitridation of cubic perovskite SrVO3 bulk yields SrV(O,N)2.8 with periodic anion-vacancy layers in the 111 direction [4]. In epitaxial thin films, the direction and periodicity of the anion-vacancy layers can be tuned by applying the strain from the substrate. Anion-ordered perovskite EuVO2H, a ferromagnet with Tc = 10 K in bulk, exhibits inter-site charge transfer from the EuH layer to the VO2 layer VO2H thin films in compressively strained thin films, leading a fourfold increase in Tc as well as a giant perpendicular magnetic anisotropy [5]. A parallel concept is exemplified in the unique magnetism of Sr2NiO2Ag2Se2 that can be obtained under high pressure, where distinct compressibilities of multiple anions play a crucial role [6].
If time permits, the seminar will also touch upon recent finding in mechanochemical reactions [7].
