Realizing negative thermal expansion over an extended temperature range in PbTiO ₃-based perovskites

Negative thermal expansion (NTE) is fascinating as it involves a material’s volume contraction rather than expansion upon heating. Although NTE lattices typically have highly flexible frameworks, the magnitude of NTE is often very small, and they frequently behave a narrow temperature range for controllable NTE. It remains a great challenge to achieve large NTE while maintaining a wide temperature operation range from the currently available materials. Herein, we present a novel PbTiO₃-based perovskite system, (1-<em>x</em>)PbTiO₃-<em>x</em>BiYbO₃, synthesized using a distinctive high-pressure and high-temperature technique. The system exhibits an unusual enhanced tetragonalities compared to pristine PbTiO₃ (<em>c</em>/<em>a</em> = 1.064). Consequently, NTE over an extended temperature range has been realized in 0.95PbTiO₃-0.05BiYbO₃ ( &nbsp;= -2.18 ´ 10^-5/K, 300 - 820 K) and 0.90PbTiO₃-0.10BiYbO₃ ( &nbsp;= -1.85 ´ 10^-5/K, 300 - 850 K), respectively, when compared to that of pristine PbTiO₃ ( &nbsp;= -1.99 ´ 10^-5/K, 300 - 763 K). Our experimental and theoretical studies indicate that the improved tetragonality and the expanded NTE temperature range result from larger ionic displacements and an enhanced asymmetric charge distribution, both induced by the BiYbO₃ substitution. The present study presents a new instance of NTE across a broad temperature range, highlighting its potential as an effective thermal expansion compensator.