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 KTaO₃, SrTiO₃, BaTiO₃, and KTa_1-xNbₓO₃ (x=0.002, 0.1, and 0.35). From the linear dependence of the electron mobility μ and the reciprocal dielectric constant 1ε on pressure in all materials studied, we conclude that μ∝1ε+const. Based on the observed temperature dependence of the Hall mobility and the Curie-Weiss behavior of ε, we conclude further that in the perovskite oxides the temperature dependence of the mobility is given by the empirical expression μ∝T^-3.5(T-T₀+T*), T>T₀, where T* is an experimental constant and T₀ is the Curie-Weiss temperature (T₀=4^∘K and T*≈140^∘K for KTaO₃, T₀=32^∘K and T*≈77^∘K for SrTiO₃, T₀=287^∘K and T*≈70^∘K for KTa0.65{Nb}0.35O₃, and T₀=395^∘K and T*≈85^∘K for BaTiO₃). 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.