Electron Scattering in Perovskite-Oxide Ferroelectric Semiconductors

This paper reports new data on the hydrostatic-pressure dependence of the conductivity and static dielectric constant, as well as new Hall-effect data taken over a wide temperature range, in the perovskite-oxide ferroelectrics KTa${\mathrm{O}}_3$, SrTi${\mathrm{O}}_3$, BaTi${\mathrm{O}}_3$, and $\mathrm{K}{\mathrm{Ta}}_{1-x}{\mathrm{Nb}}_x{\mathrm{O}}_3$ ($x=0.002, 0.1, \mathrm{and} 0.35$). From the linear dependence of the electron mobility $\mu$ and the reciprocal dielectric constant $\frac{1}{\epsilon }$ on pressure in all materials studied, we conclude that $\mu \propto \frac{1}{\epsilon }+\mathrm{const}$. Based on the observed temperature dependence of the Hall mobility and the Curie-Weiss behavior of $\epsilon$, we conclude further that in the perovskite oxides the temperature dependence of the mobility is given by the empirical expression $\mu \propto T^{-3.5\mathrm{}}(T-T_0+T^{*})$, $T>\mathrm{}{T}_0$, where $T^{*}$ is an experimental constant and $T_0$ is the Curie-Weiss temperature ($T_0=4\mathrm{}°$K and $T^{*}\approx 140°$K for KTa${\mathrm{O}}_3$, $T_0=32\mathrm{}°$K and $T^{*}\approx 77°$K for SrTi${\mathrm{O}}_3$, $T_0=287\mathrm{}°$K and $T^{*}\approx 70°$K for K${\mathrm{Ta}}_{0.65}$ ${\mathrm{Nb}}_{0.35}$ ${\mathrm{O}}_3$, and $T_0=395\mathrm{}°$K and $T^{*}\approx 85°$K for BaTi${\mathrm{O}}_3$). Our experimental results are shown to be inconsistent with previously reported suggestions that the electron mobility in the perovskite oxides is dominated by LO-mode scattering. We suggest, instead, that the electron mobility is determined by a new and strong electron-phonon interaction involving critical-point lattice-polarization fluctuations associated with the soft TO mode.