Some Transport Properties of Oxygen-Deficient Single-Crystal Potassium Tantalate (KTa<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>)

Hall-effect and electrical-conductivity measurements have been made on reduced single crystals of the perovskite potassium tantalate (KTa${\mathrm{O}}_{3}$) over the temperature range 1.6-295\ifmmode^\circ\else\textdegree\fi{}K. Lattice scattering predominates above 100\ifmmode^\circ\else\textdegree\fi{}K where the Hall mobility satisfies the empirical expression ${\ensuremath{\mu}}_{H}=8\ifmmode\times\else\texttimes\fi{}{10}^{8}{T}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{2}$/V-sec. The room-temperature value is 30 ${\mathrm{cm}}^{2}$/V-sec. Below 100\ifmmode^\circ\else\textdegree\fi{}K, ionized donor and impurity scattering become important, although mobilities as large as 23 000 ${\mathrm{cm}}^{2}$/V-sec have been observed at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results are compared with published data for the $3d$ band in isostructural SrTi${\mathrm{O}}_{3}$ and shown to be consistent with the expected larger overlap of $5d$ orbitals. Free-carrier optical-absorption measurements presented in this paper indicate that electron scattering at room temperature in KTa${\mathrm{O}}_{3}$ is mainly by the highest frequency longitudinal polar mode situated at approximately 0.12 eV. Dielectric-constant measurements have also been made. These data show an extrapolated Curie temperature of 4\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}K for KTa${\mathrm{O}}_{3}$ with nonferroelectric behavior at 1.6\ifmmode^\circ\else\textdegree\fi{}K.