Negative thermal expansion in PbTiO₃-type perovskites oxide Bi_0.5+xNa_0.5−xVO₃

Abstract

Negative thermal expansion (NTE) in Bi_0.5+xNa_0.5−xVO₃ is investigated. The parent compound, Bi_0.5Na_0.5VO₃, is a lead-free polar perovskite oxide with a tetragonal distortion comparable to that of ferroelectric PbTiO₃ owing to the ordering of d_xy 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 Bi_0.5Na_0.5VO₃ derivatives exhibit NTE when the c/a ratio is smaller than the critical value of ∼1.06.