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 KTa1-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 μ1ε+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 μT-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 KTa0.65Nb0.35O3, 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. © 1969 The American Physical Society.