Dielectric and impedance spectroscopy of NdCoIrO double perovskite.

Polycrystalline NdCoIrO double perovskite crystallizes in monoclinic crystal structure with P2/n space group. The average grain size of powder sample is 400-500 nm. The dielectric, impedance and ac conductivity of the sample were studied in the temperature range 5-300 K and in the frequency range 20 Hz-2 MHz. Dielectric constant reveals a step like increase from low temperature value of ∼5 to colossal value of ∼10 at high temperature. High value of dielectric constant is associated with Maxwell-Wagner polarization due to large grain boundary capacitance. Cations (Co and Ir) disorder leads to variable range hopping conduction of electrons in grain and grain boundary regions. Distribution of grain size induces distribution of relaxation time as confirmed from depressed semicircles in Nyquist plots. Frequency dependent conductivity follows universal power law behavior.