Study of the ferroelectricity in Bi₂Ti₂O₇ by infrared spectroscopic ellipsometry

Using infrared spectroscopic ellipsometry, the dielectric functions of (111) oriented Bi₂Ti₂O₇ thin films with pyrochlore structure prepared on Pt/Ti/SiO₂/Si substrate were determined in the temperature range of 20-70 °C. It is demonstrated that there is a phase transition that appears near 40 °C in terms of static effective charge as a function of temperature calculated from the infrared spectroscopic ellipsometric data of Bi₂Ti₂O₇ thin films. It suggests that the static effective charge is related to the structural distortion, which can facilitate the polarization of Bi ₂Ti₂O₇. Accordingly, ferroelectricity in Bi₂Ti₂O₇ is proved by analyzing the infrared dielectric function.