Crystal and Electronic Structures of Bi₄(Ti, Si)₃O₁₂ Ferroelectrics

Abstract

In this work, we synthesized Bi₄Ti₃O₁₂ and Bi₄Ti_2.85Si_0.15O₁₂ by means of a conventional solid-state reaction, and investigated their ferroelectric properties. From P-E hysteresis measurement, it was demonstrated that the Bi₄Ti₃O₁₂ began to show higher remanent polarization and lower coercive field by partially substituting Si for Ti. In order to clarify how the substitution affected the crystal and electronic structures and thus ferroelectric properties, we performed X-ray absorption fine structure spectroscopy, synchrotron X-ray diffraction and neutron diffraction measurements. As a result, it was found by Rietveld analysis using neutron diffractions that local distortions of TiO₆ octahedra increased by the partial substitution of Si for Ti. Taking it into account that such a distortion induces a polarization in a crystal, this may be one of the reasons why the substitution improved ferroelectric properties of Bi₄Ti₃O₁₂. From electronic density distributions estimated by maximum entropy method, it was also suggested that Ti-O bond became stronger by the substitution.