Berlin 2008 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 3: Phase Transitions

DF 3.2: Talk

Monday, February 25, 2008, 11:00–11:20, EB 407

Transformation from ferroelectric to relaxor state in BaTiO₃ based relaxor ferroelectrics — •Vladimir Shvartsman¹, Wolfgang Kleemann¹, Jan Dec², Sheng-Guo Lu³, Zheng Kui Xu³, and Jiwei Zhai⁴ — ¹Angewandte Physik, Universität Duisburg-Essen. Duisburg, Germany — ²Institute of Physics, University of Silesia, Katowice, Poland — ³Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China — ⁴Functional Materrials Research Laboratory, Tongji University, Shanghai, China

Presently considerable interest is focused onto the investigation of environment-friendly lead-free relaxors, in particular those based on the ferroelectric BaTiO₃. In these materials relaxor properties are observed not only at heterovalent cation substitution as in most relaxors, but also at isovalent substitution. We report on results of investigations of Ba(Ti_1−xSn_x)O₃ (BTSn) and Ba(Ti_1−xZr_x)O₃ (BTZ), x=0.1-0.4, ceramics which show a gradual transformation from ferroelectric to relaxor behavior at decreasing titanium content. Low-frequency dielectric spectroscopy and piezoresponse force microscopy were applied in order to distinguish the ferroelectric and relaxor features. The ferroelectric state is evidenced in BTSn and BTZ with x < 0.175 and 0.25, respectively. The broadening of the peak of the dielectric permittivity ("diffuse phase transition") is due to the coexistence of ferroelectric domains and paraelectric regions related to a nanoscale compositional segregation into Ti-rich and Ti-depleted regions. Further decrease of Ti-content results in relaxor behavior, which is supposed to be related both to weak random fields and to disorder inherent in pure BaTiO₃.