Realization of Negative Thermal Expansion in Lead-Free Bi_0.5K_0.5VO₃ by the Suppression of Tetragonality

Abstract

Bi1/2K1/2VO3 is a lead-free PbTiO3-type compound with a tetragonality (c/a = 1.054) comparable to that of typical ferroelectric PbTiO3 (c/a = 1.064) with negative thermal expansion (NTE) during the tetragonal-to-cubic phase transition; therefore, Bi1/2K1/2VO3 is a potential lead-free NTE material if its metastable perovskite structure can be maintained at high temperatures. In the present experiment, electron doping in Bi1/2K1/2VO3 was conducted through substituting K+ with La3+ to suppress the tetragonality and achieve NTE. La substitution successfully suppressed the tetragonality of Bi1/2K1/2VO3 and also improved its thermal stability. Moreover, both composition- and temperature-induced tetragonal-to-cubic phase transitions occurred. In particular, a large volume shrinkage with a large negative thermal coefficient of expansion (CTE) was obtained for Bi0.5K0.46La0.04VO3 during the tetragonal-to-cubic phase transition (ΔV = −0.66%). Hence, this study extends the NTE family and also sheds light on the exploration of lead-free piezoelectric materials with controllable thermal expansion.

Two Types of Negative Thermal Expansion Observed in PbCr1–xTixO3

“…Materials exhibiting negative thermal expansions (NTEs) have attracted much attention because these can potentially compensate for the thermal expansion of structure materials by forming composites. − The last decade has seen remarkable development in materials with NTEs resulting from phase transition. In particular, compounds with perovskite-type structures (BiNiO 3 derivatives, − PbTiO 3 -type polar oxides, − and A-site ordered quadruple perovskites − ) and their related structures such as anti-perovskites (Mn nitrides , ), layered perovskites (Ca 2 RuO 4– y , ), and ReO 3 -type compounds (ScF 3 , ) have been reported as giant NTE materials.…”