Realization of Negative Thermal Expansion in Lead-Free Bi 0.5 K 0.5 VO 3 by the Suppression of Tetragonality.

Bi 1/2 K 1/2 VO 3 is a lead-free PbTiO 3 -type compound with a tetragonality ( c / a = 1.054) comparable to that of typical ferroelectric PbTiO 3 ( c / a = 1.064) with negative thermal expansion (NTE) during the tetragonal-to-cubic phase transition; therefore, Bi 1/2 K 1/2 VO 3 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 Bi 1/2 K 1/2 VO 3 was conducted through substituting K + with La 3+ to suppress the tetragonality and achieve NTE. La substitution successfully suppressed the tetragonality of Bi 1/2 K 1/2 VO 3 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 Bi 0.5 K 0.46 La 0.04 VO 3 during the tetragonal-to-cubic phase transition (Δ V = -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.