Study on diffuse dielectric anomaly at high temperature region in perovskite-type ferroelectric oxides

Abstract

The dielectric relaxation behavior at high temperature region (400~700℃) was investigated in various perovskite-type ferroelectric oxide systems. It is known as diffuse dielectric anomaly or rounded dielectric anomaly. It is commonly found at the same temperature range of 400~700℃ in various perovskite-type ferroelectric oxides such as $BaTiO_3$, $PbTiO_3$, $CaTiO_3$, $SrTiO_3$ and their solid solutions. Although previously suggested dielectric relaxation models explained partly the dielectric relaxation phenomenon of the diffuse dielectric anomaly, there have been still remained unclear. For example, the frequency dependence of the diffuse dielectric anomaly was perfectly understood by the Debye relaxation model. However, the temperature-dependent behavior of the diffuse dielectric has not been understood. Therefore, the dielectric relaxation behavior of the diffuse dielectric anomaly at high temperature region was systematically studied in both experimental and theoretical ways, in this study. In the first chapter, the diffuse dielectric anomaly was experimentally investigated in various perovskite-type ferroelectric oxides such as $BaTiO_3$ single crystal and ceramics, La-doped $PbTiO_3$ ceramics, and $Pb_{1-x}La_xZr_{0.4}Ti_{0.6}O_3(x=0, 0.01, 0.05, 0.1)$ ceramics. The effects of sintering atmosphere, heat treatment and additives on the diffuse dielectric anomaly were observed, which strongly confirmed that the diffuse dielectric anomaly was related with oxygen vacancies. Also, it was found that the diffuse dielectric anomaly was perfectly suppressed in highly donor-doped PLZT ceramic systems. The theoretical approach with Debye relaxation model was performed to understand the dielectric relaxation behavior of the diffuse dielectric anomaly in the second chapter. Conventionally, the relaxation time has been known as a main parameter between experimental results and the Debye relaxation model. However, the modified fitting method with the relaxation streng...