Study of electrical and dielectric properties of Sr3CoSb2O9 perovskite by impedance spectroscopy

Triple perovskite Sr3CoSb2O9 was found to be orthorhombic having space group Immm from the Rietveld refinement of X-ray diffraction data. Impedance analysis of Sr3CoSb2O9 was performed to study the presence of different electro-active regions, electrical transport mechanism and origin of colossal dielectric constant in the temperature and frequency range of 273–423 K and 40 Hz–3 MHz, respectively. An equivalent circuit model (RgCg)(RgbQgb)(ReQe) was used to explain the complex impedance plane plots. The Rg and Rgb derived from Z View fitting of the impedance (Z) data reflect semiconducting behavior of Sr3CoSb2O9. Reduction in Z′ was observed as a function of temperature and frequency which indicates increase in ac conductivity and negative temperature coefficient of resistance. In order to explain the electrical conduction mechanisms in grains and grain boundaries the variable range hopping model was employed. AC conductivity as a function of frequency follows Jonscher’s power law. The ac conduction mechanism was explained from temperature dependent variation of frequency exponents n1 and n2. The modulus analysis confirmed the presence of non-Debye type multiple relaxation mechanisms. Dielectric properties of the sample were also investigated in the temperature range 273–423 K. At higher frequencies reduction in dielectric loss was observed.