Complex impedance studies on a layered perovskite ceramic oxide -: NaNdTiO4

A layered perovskite ceramic oxide, NaNdTiO4, has been prepared by a standard solid-state reaction technique. Compound formation and phase identification has been confirmed by X-ray diffraction (XRD) studies. The material has been found to contain NaNdTiO4 as the predominant phase together with a minor impurity phase of Na2Nd2Ti3O10. Sample microstructure, observed through scanning electron microscopy, appears to be polycrystalline with shape anisotropy. Complex impedance analysis of the sample has indicated (i) the presence of grain boundary effects at temperatures above 200degreesC; (ii) negative temperature coefficient of resistance (NTCR) effect; and (iii) evidence of multiple electrical relaxation phenomena in the sample. The sample impedance behavior has been explained in terms of brick-layer model. The impedance measurements have shown the evidence of grain boundary conduction and lowering of barrier to the motion of charge carriers with rise in temperature. Electrical conductivity (sigma(dc)) as evaluated from complex impedance spectrum, shows a large jump in the value at higher temperatures (similar to1.66 x 10(-4) S cm(-1) at 550degreesC) when compared to the room temperature conductivity value (similar to4.5 x 10(-9) S cm(-1)). It has been attributed to the weakening of the interaction between the interlayer sodium ion and the perovskite layer. The results of ac conductivity as a function of frequency are also discussed. (C) 2004 Elsevier B.V. All rights reserved.