Dielectric spectroscopic study of (K_0.44Na_0.52Li_0.04)_0.97 La_0.01Nb_0.9Ta_0.10₃ ceramics

A dielectric spectroscopic study and an ac conductivity analysis in the 100 Hz–1 MHz frequency and 30–450 °C temperature ranges are presented for the piezoceramic compound (K0.44Na0.52Li0.04)0.97La0.01Nb0.9Ta0.103, synthesized by the traditional ceramic method using NaNbO3 as a precursor obtained by the reactive templated grain growth method technique. La doping of KxNa1-xNbO3 (KNN) produces a shift of the phase transition temperatures (orthorhombic-tetragonal and tetragonal-cubic) toward lower temperatures. The measured relative permittivity maximum and the relative permittivity at room temperature are remarkably high. Conductivity behaves according to Jonscher's law in the 400 Hz–1500 Hz frequency range at temperatures between 75 and 300 °C, with values of n1≤ 0.70, lower than those reported in the literature for similar compounds. The activation energy in the case of dc (long range) conductivity, 1.72 eV, points out to double ionized oxygen vacancies. This value is higher than the 1.46 eV of undoped KNN, evincing the influence of Li and La in the conduction processes of KNN.