Electron–relaxation-mode interaction inBaTiO3:Nb

Dielectric relaxation was previously reported in ${\mathrm{BaTiO}}_3$ and ${\mathrm{BaTiO}}_3$:Fe single crystals at radio frequencies [M. Maglione et al., Phys. Rev. B 40, 11 441 (1989)]. We have measured the dielectric dispersion in four ${\mathrm{BaTiO}}_3$:Nb samples (${\mathit{x}}_{\mathrm{Nb}}$<0.3 at. %) as a function of frequency (10<f<${10}^9$ Hz) and temperature (20<T<450 K). The electronic conductivity of ${\mathrm{BaTiO}}_3$:Nb enhances drastically the relaxation step at all temperatures. In the rhombohedral phase of ${\mathrm{BaTiO}}_3$:Nb (T<180 K), an unusual slowing down of the relaxation motion is measured. The relaxation time increases to more than ${10}^{\mathrm{-}2}$ 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.