Role of initial potassium excess on the properties of potassium tantalate ceramics

Potassium tantalate (KTaO3 – KT) ceramics with controlled initial K/Ta ratio = 1, 1.02 and 1.05 were synthesised by solid-state reaction. Crystal structure and microstructure of the sintered ceramics were examined by XRD and SEM/EDS, respectively. Their dielectric properties were then studied as a function of the temperature over the radio frequency range. Ceramics with K/Ta ratio = 1 exhibits potassium-poor secondary phases, in contrast to ceramics with initial K/Ta ratio = 1.05, where no secondary phases are detected. Moreover, the grain size increases dramatically with K/Ta ratio >1. The quantum paraelectric behaviour of KT ceramics is weakly affected by the variation of K/Ta ratio and their dielectric response is well described by Barrettʹs equation. Though, no anomaly is induced in the dielectric permittivity by potassium excess, it yields an increase of its lowest temperature magnitude up to ∼4000, which is to the best of our knowledge, the highest value ever reported for KT ceramics.