ELECTRON RELAXATION-MODE INTERACTION IN BATIO3-NB

Dielectric relaxation was previously reported in BaTiO3 and BaTiO3:Fe single crystals at radio frequencies [M. Maglione et al., Phys. Rev. B 40, 11441 (1989)]. We have measured the dielectric dispersion in four BaTiO3:Nb samples (x(Nb) < 0.3 at. %) as a function of frequency (10 < f < 10(9) Hz) and temperature (20 < T < 450 K). The electronic conductivity of BaTiO3:Nb enhances drastically the relaxation step at all temperatures. In the rhombohedral phase of BaTiO3:Nb (T < 180 K), an unusual slowing down of the relaxation motion is measured. The relaxation time increases to more than 10(-2) s at 20 K while the relaxation step is temperature independent. The precursor effect of this slowing down is a maximum in the dc conductivity. A simple electron-relaxation-mode coupling model may explain such behavior.