Structural investigation, vibrational study, and Na-ion transport properties of NaGaP₂O₇ as sodium solid electrolyte

Searching for new a family of phosphates is of special importance to enrich the basic database of the structure and properties for developing inorganic compounds. In the current study, we have investigated the sodium diphosphate NaGaP₂O₇ sample, synthesized by the classical solid-state method. The Rietveld refinement results indicate a single phase with a monoclinic structure (space group P2_1/C). The average grain size was approximately around 18 µm. Vibrational study (IR, Raman) at room temperature confirmed the presence of the P₂O₇ functional group. The impedance spectra show that the electrical properties of the sample are heavily dependent on the frequency and temperature, indicating a relaxation phenomenon and semiconductor-type comportment. Nyquist plots were explored using an equivalent circuit, including a parallel combination of resistance and fractal capacity. The AC conduction mechanism in the material under investigation was clarified by applying correlated barrier hopping (CBH) and non-small polaron tunneling (NSPT) models. These findings suggest that the material shows promising potential as a cathode material.