Temperature and frequency dependent electrical properties of SrTi[formula omitted]Ta[formula omitted]O[formula omitted] ([formula omitted]) ceramics

Abstract

Lead free Ta substituted SrTiO3 (SrTi1−xTaxO3, x = 0.00 ≤x≤ 0.15) are prepared by solid-state reaction technique sintered at 1300 °C for 3 hr. The structural and morphological studies are characterized by XRD, FE-SEM and TEM. The electrical properties of Ta doped SrTiO3 (SrTi1−xTaxO3) samples are studied at elevated temperatures (400 °C–500 °C) in a broad frequency range (100 Hz–5 MHz). Rietveld refinement of the XRD data confirms the single phase formation of SrTi1−xTaxO3 samples having cubic symmetry with space group Pm3¯m. The crystallite size (D) is calculated for all the samples using Williamson–Hall (W–H) formula. The FE-SEM images show a reduction in the average grain size from 342 nm to 157 nm with increasing Ta content. Maxwell–Wagner polarization mechanism explains the dielectric characteristics of the synthesized samples which is effective at high temperature and low frequency. The dielectric, conductivity and impedance analysis attribute to the space charge polarization, hopping mechanism and negative temperature coefficient of resistance (NTCR) characteristics of the material. Nyquist analysis reveals that both grain and grain boundary play a significant role in the conduction process of SrTi1−xTaxO3 ceramics. The frequency dependent ac-conductivity is analyzed using Jonscher’s universal power law and follows the correlated barrier hopping (CBH) mechanism. Activation energies are estimated from the dc-conductivity ranges from 0.62–0.70 eV and suggest that a thermally activated charge transport mechanism is involved in the conduction process of SrTi1−xTaxO3 ceramics.