Structural and complex AC impedance spectroscopic studies of A2CoNbO6 (A = Sr, Ba) ordered double perovskites

Powder X-ray diffraction has been employed to study the crystal structures of Sr2CoNbO6 (SCNO) and Ba2CoNbO6 (BCNO) double perovskites. Rietveld fit to the X-ray diffraction data showed that Ba2CoNbO6 perovskites was monoclinic with space group P21/n whereas Sr2CoNbO6 was found to be tetragonal with space group I4/m. Like other cobalt based perovskites, both materials exhibit high values of dielectric constant at room temperature and low frequencies. Room temperature impedance and modulus spectra, measured over the 1 Hz to 10 MHz, reveal two relaxation processes with different relaxation times which were attributed to the grain and grain boundaries.

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