Dielectric and impedance spectroscopy of Sm2CoIrO6 double perovskite

•Giant dielectric constant (~103) is observed close to room temperature.•Distribution of relaxation time has been described by Cole-Cole model.•AC conductivity in the low temperature region has been described by Jonscher’s augmented equation.•Deviation from the universal dielectric response (UDR) has been observed at high temperature and can be described by jump relaxation model (JRM). Deviation from universal dielectric response at high temperature and described by jump relaxation model consequently. Polycrystalline double perovskite Sm2CoIrO6 (SMCO) ceramics have been prepared by solid state reaction to investigate dielectric properties. X-ray investigation confirms the formation of single phase with monoclinic crystal structure with space group P21/n. Scanning electron microscopy (SEM) reveals the microstructural features with an average grain size of 543 nm. Dielectric, impedance and ac conductivity of the sample were studied in the temperature range 5 – 270 K and frequency range 100 Hz – 2 MHz. Temperature dependent dielectric constant reveals a giant step (~103) which saturates at high temperature ~ 250 K. Distribution of grain size leads to a distribution of dielectric relaxation time which has been described by Cole-Cole relaxation. Coupling of Maxwell-Wagner polarization and polaronic relaxation is evident from the impedance and ac conductivity analysis.