High frequency dielectric spectroscopy of relaxor ferroelectrics and related materials

Relaxor and doped incipient ferroelectrics represent the partially disordered solids, where the main lattice periodicity is preserved and only some of the sublattices exhibit disorder. Dielectric response of these polar materials is defined by both crystal lattice dynamics and relaxational processes in a wide frequency range below the phonon frequencies. High frequency part of the response is very important for studying the nature of disorder and the relation between the relaxation processes and the crystal lattice dynamics. Here we analyze the high frequency dielectric response (1 MHz - 100 THz) of model lead-containing perovskite relaxor ferroelectrics (PMN, PLZT), moderately doped incipient ferroelectrics (Sr_1-1.5xBi_xTiO₃ and K_1-xLi_xTaO₃) and pyrochlore high-ε microwave ceramics ((Bi,Zn)₂(Zn,Nb)₂O₇), studied by the coaxial and waveguide microwave methods, time domain THz spectroscopy and infrared reflectivity.