Structural, dielectric and electrical properties of Sr5GdTi3X7O30 (X = Nb and Ta) ceramics: an impedance spectroscopic study

Polycrystalline samples of Sr5GdTi3Nb7O30 and Sr5GdTi3Ta7O30 ceramics were prepared by a high-temperature solid state reaction technique. The formation of single-phase compounds in the orthorhombic system has been confirmed by room temperature X-ray diffraction studies. Scanning electron micrographs of the sintered samples were recorded at room temperature to study the surface morphology and the grain distribution over the surface. It has been found that the grain size decreases on substitution of Ta5+ in the Nb5+ site. Detailed studies of the dielectric constant (ε) and loss tangent (tanδ) with frequency at different temperatures suggest that both the compounds have a dielectric anomaly or diffuse nature. It was interesting to observe that the transition temperature (Tc) shifts to the low temperature side after Ta5+ is substituted at the Nb site or Sr5GdTi3Nb7O30. Detailed analysis of the impedance data suggests that the conduction processes is due to both bulk as well as grain boundary contributions. The scaling behaviour of the loss spectra of the material suggests that the distribution of relaxation time is temperature dependent and polydispersive in nature. The frequency dependent electrical properties of the compounds were also studied. (author)