Dielectric anisotropy in relaxor ferroelectric Pb_(0.775)La_(0.15)(Zr_(0.4)Ti_(0.6))O_3 ceramics

摘要

A huge dielectric anisotropy has been found in Pb_(0.775)Lag_(0.15)(Zr_(0.4)Ti_(0.6))O_3 (PLZT 15/40/60)rnceramics by analysis of infrared reflectivity spectra. Anisotropy is present in both the relaxor and the ferroelectric phases. Infrared spectra were evaluated using Bruggeman's formula within the effective medium approximation. X-ray structural analysis supports a local [110] shift of Pb cations and factor-group analysis taking into account the Ad site symmetry for the effective Pb/La atom gives more infrared and Raman active phonons than the previous published factor-group analysis, in agreement with our infrared data. Symmetry of all observed polar phonons was assigned.