The dielectric response of quantum paraelectrics containing dipole impurities

The presence of even a very small concentration of slowly reoriented dipole impurities in a quantum paraelectric leads to strong changes in the dielectric response of the sample. This is manifested by the appearance of a giant dielectric susceptibility, colossal frequency dispersion, and several peaks in the temperature dependence of the susceptibility; in addition, the temperature dependence of the relaxation time deviates from exponential. The experimental results are presented for KTaO3 samples slightly or moderately doped with lithium. General relationships between the dielectric response and the concentration of impurities, the temperature, and the frequency are established. A theory is proposed which qualitatively explains the observed complex phenomena and sometimes quantitatively describes the results with high precision. (C) 2002 MAIK "Nauka / Interperiodica".