Mechanism for suppression of ferroelectricity in Cd1-xCaxTiO3

A mechanism for cation-substitution-induced suppression of ferroelectricity in a perovskite-type ferroelectric oxide, CdTiO3, has been elucidated in terms of the relationship between the covalency and the lattice dynamics. Raman scattering experiments and first-principles calculations clarified that a change in the covalency of Cd sites due to Ca substitution selectively decreases the frequencies of the modes associated with octahedral rotations whose axes are perpendicular to the spontaneous polarization direction. The resulting destabilization of zigzag octahedral chains synchronizes the hardening of the ferroelectric soft mode, which suppresses the ferroelectricity. This result enhances our understanding of the relationship between local chemical bonds and macroscopic ferroelectricity.