Perovskite oxides ABO₃ continue to be a major subject in materials science because of its chemical and structural diversity1. Of particular interest is the interplay between A and B cations with finite d/f electrons, which, for example, causes inter-site charge transfer (ICT), leading to novel phenomane such as negative thermal expansion and metal-to-insulator transitions. The ICT properties are controlled by cationic substitution, but the mechanism is complicated by three-dimensional (3D) structures. Mixed-anion compounds began to draw attention as game-changing inorganic materials. Since, compared with conventional inorganic compounds such as oxides, mixed-anion compounds may exhibit unique coordination and resultant extended structures, from which fundamentally different chemical and physical property may emerge. In my talk, a new oxyhydride EuVO₂H, prepared via anion-exchange reactions of EuVO₃perovskite oxide, will be presented [1]. EuVO₂H with alternating layers of EuH and VO₂ exhibit ICT between the heteroanion layers. While bulk EuVO₂H is a ferromagnetic insulator with T_C = 10 K, application of external pressure or biaxial strain from a substrate to a EuVO₂H film causes ICT to occur from the Eu^IIH layer to the V^IIIO₂ layer. The strained film exhibits a 4-fold increase in T_C and, despite the absence of orbital angular momentum, Eu²⁺ exhibits giant magnetic anisotropy with its easy axis perpendicular to the film, which is favorable for devices such as high-density memory. The present results provide new possibilities for the acquisition of novel functions by alternating layered structures of heteroanions. If time allows, other examples of strain engineering of perovskite structures and properties including SrV(O,N)3-x [2]will be presented.

References:
[1] Nambe et al., submitted.
[2] Yamamoto et al., Nat. Commun 11, 5923 (2020)