*

PbTiO₃ is an important technological material due to its high-temperature ferroelectricity, piezoelectricity, and negative thermal expansion. Previous theoretical work has predicted an anomalously large elastic compliance in PbTiO₃ that can be induced by negative pressure¹, stress^2,3, or strain³, and could potentially be exploited in applications requiring large tailored piezoelectric and elastic responses. The microscopic mechanism of this anomalous behavior remains unknown but has been hypothesized to involve breaking of the Ti-O bond along the polarization direction.¹

In this work, we use a newly developed first-principles-based energy partitioning procedure to show that the microscopic origin of the elastic anomaly in PbTiO₃ is a competition between the ionic lattice response and collective electronic interactions, and is surprisingly dominated by the Pb-O bond, rather than the Ti-O bond. Our insights into the chemical origin of the elastic anomaly further position PbTiO₃ as a key material for the study of functionally important competing collective behavior and phase transitions.

1) S. Tinte, et al. PRB 68, 144105 (2003).

2) Y. Duan, et al. J. Phys. Condens. Matter 20, 17 (2008).

3) H. Sharma, et al. PRB 90, 214102 (2014).