High-Pressure Synthesis, Crystal Structure, Chemical Bonding, and Ferroelectricity of LiNbO₃-Type LiSbO₃

A polar LiNbO₃ (LN)-type oxide LiSbO₃ was synthesized by a high-temperature heat treatment under a pressure of 7.7 GPa and found to exhibit ferroelectricity. The crystal structural refinement using the data of synchrotron powder X-ray diffraction and neutron diffraction and the electronic structure calculation of LN-type LiSbO₃ suggest a covalent-bonding character between Sb and O. When comparing the distortion of BO₆ in LN-type ABO₃, the distortions of SbO₆ in LiSbO₃ and SnO₆ in ZnSnO₃, which included a B cation with a d¹⁰ electronic configuration, were smaller than those of BO₆ in LN-type oxides having the second-order Jahn-Teller active B cation, e.g., LiNbO₃ and ZnTiO₃. The temperature dependence of the lattice parameters, second harmonic generation, dielectric permittivity, and differential scanning calorimetry made it clear that a second-order ferroelectric-paraelectric phase transition occurs at a Curie temperature of T_c = 605 ± 10 K in LN-type LiSbO₃. Further, first-principles density functional theory calculation suggested that perovskite-type LiSbO₃ is less stable than LN-type LiSbO₃ under even high pressure, and the ambient phase of LiSbO₃ directly transforms to LN-type LiSbO₃ under high pressure. The phase stability of LN-type LiSbO₃ and the polar and ferroelectric properties are rationalized by the covalent bonding of Sb-O and the relatively weak Coulomb repulsion between Li⁺ and Sb⁵⁺.