2022 年 130 巻 8 号 p. 691-695
Negative thermal expansion (NTE) in Bi0.5+xNa0.5−xVO3 is investigated. The parent compound, Bi0.5Na0.5VO3, is a lead-free polar perovskite oxide with a tetragonal distortion comparable to that of ferroelectric PbTiO3 owing to the ordering of dxy orbital of V4+ with d1 electronic configuration. The c/a ratio was decreased by electron doping to V4+ through increasing Bi3+/Na+ ratio and transition to a non-polar cubic phase on heating accompanied by NTE with a large volume shrinkage of −2.28 % was enabled. It is found that the Bi0.5Na0.5VO3 derivatives exhibit NTE when the c/a ratio is smaller than the critical value of ∼1.06.