Dielectric relaxation and predominance of NSPT and OLPT conduction processes in Ba0.9Sr0.1TiO3

We investigate the relaxation and conduction mechanism of Ba0.90Sr0.10TiO3 (BST) ceramic, synthesized by the solid state reaction method. The dielectric and relaxation properties are analyzed in the temperature range of 380-450 degrees C with alternative current in the frequency range of 20 Hz-1MHz. Variation of dielectric constant, epsilon', with temperature shows a normal ferroelectric transition at T-c = 95 degrees C with a weak degree of diffuseness. The modified Cole Cole equation is used to describe all contributions to the relaxation mechanism. The frequency exponent m(omega,T) deduced from experimental data of the dielectric loss (epsilon '') as m(omega, T) = (partial derivative ln epsilon ''/partial derivative ln omega)(T) shows a temperature and frequency dependence. Two conduction process are observed: non-overlapping small-polaron tunneling (NSPT) at low frequencies and overlapping large polaron tunneling (OLPT) at high frequencies. The analysis of Nyquist plots reveals also the presence of two contributions, who which the activation energies have been calculated. (C) 2017 Elsevier Ltd. All rights reserved.