Bi-0 covalency in PbTi0₃-Biln0₃ with enhanced ferroelectric properties : Synchrotron radiation diffraction and first-principles study

High-Tc ferroelectric (1 -X )PbTiO₃.r.xBilnO₃shows a sustainable spontaneous polarization in tetragonal phase by amount of BilnO₃ augmented. It is rare and interesting that weak ferroelectric In³ substitution does not reduce ferroelectricity as most of BiMeOs materials. To understand this abnormality behavior, the structure and the cation displacements arc studied by means of synchrotron radiation diffraction. The cation displacements of A-site atoms and B-site atoms exhibit a coupling property. Their sustainedly increasing trend is quantitatively associated with spontaneous polarization. Moreover, the structure, the valence electron density distributions, electron localization function, and Bader analysis have been researched on the chemical bond in (1 -X )PbTiO₃.r.xBilnO₃ through first-principles calculations here. Although In atoms substitution reduces the covalency degree, this loss is offset by enhanced covalency between Bi-O bonds. The crucial role of Bi atom substitution not only contributes to enhance the covalency but also promotes the polarization.