Synthesis and ionic conductivity of phosphate-sulfate fluorapatites Ca10-xNax(PO4)6-x(SO4)xF2 (x = 0, 3, 6)

•Phosphate-sulfate fluorapatites Ca10-xNax(PO4)6-x(SO4)xF2 (x = 0, 3, 6) were synthesized by the solid-state reaction.•XRD and TEM techniques confirmed the formation of single apatite phases crystallizing in the hexagonal system.•The ionic conductivity follows the Arrhenius and the Jonscher laws.•The Ca7Na3(PO4)3(SO4)3F2 (x = 3) apatite is the better conductor than the end members. Phosphate-sulfate fluorapatites Ca10-xNax(PO4)6-x(SO4)xF2 (x = 0, 3, 6) have been synthesized by the solid-state reaction at high temperature. The samples have been characterized by X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy and Transmission Electron Microscopy (TEM) techniques. XRD study shows that these materials crystallize in the hexagonal system with P63/m as a space group. An impedance analysis has been used to analyze the electrical behavior of the samples at different temperatures. Evidence of temperature-dependent electrical relaxation phenomena is observed. The bulk resistance decreases with increasing temperature, showing a typical negative temperature coefficient of resistance (NTCR). Ac-conductivity measurements have been performed on a wide range of frequencies and temperatures. The ionic conductivity follows the Arrhenius and the Jonscher laws.