Tolerance Factor Control of Tetragonality and Negative Thermal Expansion in PbTiO₃-Based Ferroelectrics

The exploration of materials with large negative thermal expansion (NTE) is highly demanded but remains challenging because chemical substitution generally tends to weaken the NTE effect of currently available NTE materials. Herein, we proposed a tolerance factor (t)-tetragonality (c/a) relationship in order to achieve enhanced NTE in PbTiO3-based ferroelectrics. According to this guidance, we designed a new Pb/Bi-based perovskite of (1 – x)PbTiO3-xBiYO3. The present new system exhibits an unusual increased tetragonality (c/a = 1.073) compared to pristine PbTiO3 (c/a = 1.064). As a result, enhanced NTE with an average volumetric coefficient of thermal expansion of α̅V = −2.34 × 10–5/K has been successfully achieved in an extended temperature range from room temperature (RT) up to 840 K for the 0.90PbTiO3-0.10BiYO3 compound, which is contrasted with that of pristine PbTiO3 (α̅V = −2.11 × 10–5/K, RT to 800 K). The present study not only paves the way for the design of large NTE in PbTiO3-based ferroelectrics, but also has great impact on the understanding of structure–property relationships so as to provide a new design to optimize NTE performance.