Grain and grain boundary relaxation in Sr 1 -x La x Ti 1 -x Cr x O 3 ceramics: Impedance and modulus spectroscopy

Abstract

T he structure and dielectric behaviour of the valence compensated system Sr_{1 -x}La_xTi_{1 -x}Cr_xO₃ (x • 0·50) have been studied. Complex plane and spectroscopic studies of the impedance and modulus functions have been made in the temperature range 100-550 K to separate out the various contributions to the overall polarisation/electrical behaviour. The immittance data of various compositions in the system can be modelled by an equivalent circuit containing three parallel RC elements connected in series. These three elements correspond to the grain (bulk), grain boundaries, and electrode/specimen interface. It has been observed that the resistance of grain boundaries in all samples except x = 0·05 is higher than that of the grains. At low temperatures the contribution of electrode polarisation to total observed resistance is small in comparison with that of the grains and grain boundaries, and becomes significant only at high temperatures. Debye type relaxation owing to reorientation of dipoles is observed within the grains at low temperatures. With increasing temperature, Maxwell-Wagner type polarisation is observed at grain/grain boundary interfaces. The relaxation observed at high temperatures and low frequencies corresponds to electrode/specimen interface polarisation.