Extend the scope of negative thermal expansion in PbTiO3-based perovskites

PbTiO3 is a typical perovskite-type ferroelectric that shows unique negative thermal expansion (NTE) from room temperature to its Curie temperature (α¯V = −1.99 × 10−5 K−1, 300–763 K). It is widely accepted that enhanced NTE can be achieved in PbTiO3-based ferroelectrics by improving the tetragonality of PbTiO3 (c/a = 1.064) through chemical substitutions. Nevertheless, most substituted PbTiO3-based ferroelectrics exhibit reduced tetragonality and weakened NTE, while enhanced NTE has only been achieved in those materials with enhanced tetragonality so far. Herein, we report on (1 − x)PbTiO3-xBiAlO3 solid solutions for which we observe reduced tetragonality accompanied by an unusual enhanced NTE (c/a = 1.057, α¯V = −2.23 × 10−5 K−1, 300–740 K), without much degradation of the NTE temperature range of pristine PbTiO3 upon doping. The present study provides an example of unusual enhanced NTE accompanied by reduced tetragonality in PbTiO3-based perovskites, which will extend the scope of NTE in PbTiO3-based ferroelectrics and shed light on the understanding of enhanced NTE in PbTiO3 family.