  Potassium tantalate (KTaO$_{3}$) is a promising material for dielectric
applications at low temperature. However, dense and single-phase ceramics
cannot be obtained by conventional sintering because of the evaporation of
potassium that leads to secondary phases. Here, we demonstrate that spark
plasma sintering is a suitable method to obtain dense and single-phase
KTaO$_{3}$ ceramics, by optimizing three parameters: initial composition,
temperature, and pressure. A 2 mol% K-excess in the precursors leads to a large
grain growth and dense single-phase ceramics. Without K-excess, a small amount
of secondary phase (K$_{6}$Ta$_{10.8}$O$_{30}$) is observed at the surface but
can be removed by polishing. At 10 K, the dielectric permittivity is 4 times
higher in the ceramic from the 2 mol% K-excess powder, because of the larger
grain size. The thermal conductivity decreases with decreasing grain size and
stays above the thermal conductivity of KNbO$_{3}$ ceramics.
