Electrical properties and conduction mechanism in sodiumcobalt orthophosphate compounds

The β-NaCoPO4 and γ-NaCoPO4 materials were prepared using the mechanical milling technique followed by heat treatment. The investigated samples were characterized by combining X-ray powder diffraction, scanning electron microscopy (SEM), thermal analysis and electrical impedance spectroscopy techniques. The Rietveld refinement of X-ray diffraction (XRD) pattern revealed that these β-NaCoPO4 and γ-NaCoPO4 phases are indexed in the hexagonal and monoclinic system with P61 and P21/n space group, respectively. The grain shapes illustrate homogeneous particle size distribution. Differential scanning calorimetric (DSC) for the β-NaCoPO4 and γ-NaCoPO4 disclosed a single-phase transition at 506 K and 560 K respectively. Furthermore, the electrical and dielectric properties of these materials have been investigated using complex impedance spectroscopy between 1000 Hz and 2 MHz at various temperatures (400–600 K). The temperature dependence of the exponent S suggests that the conduction of β-NaCoPO4 compound is interpreted in the first phase (I) by the OLPT model and the second by the NSPT model, while γ-NaCoPO4 can be attributed to the CBH model.