Rietveld refinements, impedance spectroscopy and phase transition of the polycrystalline ZnMoO4 ceramics

The triclinic phase of zinc molybdate α-ZnMoO4 (ZMO) was synthesized by a simple co-precipitation method at 600°C. The crystal structure of the obtained polycrystalline sample of ZMO was characterized by X-ray diffraction (XRD) and Rietveld calculations using the space group P-1. The electrical properties of α-ZnMoO4 compacted pellets were determined at room temperature from electrical impedance spectrometry (EIS), in the temperature range of 400–700°C. Nyquist representations were interpreted in terms of two types of electrical circuits, involving a high frequency bulk component and a low frequency Warburg component. Analyses of the frequency dependence of the real and imaginary impedance show a non-Debye type relaxation. A phase transition corresponding to the allotropic transformation triclinic–monoclinic (α→β) of ZnMoO4 was observed in the temperature range of 450–500°C, with a variation of activation energies. The Warburg component is discussed in terms of electrode surface reactions.