Dielectric properties and AC conductivity behaviour of rare earth-substituted yttrium strontium silicate oxy-apatite

The dielectric properties and AC conductivity behaviour of yttrium strontium silicate oxy-apatite (YSSO) compounds substituted with europium ions as rare earth, Y_8–xSr₂(SiO₄)₆O₂: xEu, x = 0, 0.10, 0.15, 0.20, 0.25 and 0.30 mol% (YSSO: xEu), prepared by solution combustion method has been reported here. The XRD and Rietveld refinement patterns confirmed the formation of a hexagonal closed-packed structure with space group P6₃/m and space group number 176. The morphological analysis was carried out by scanning electron microscopy, which showed random distribution of particles. The elemental analysis was done by EDXS, which gave the atomic% and weight% of all the initial elements present in the compound. The frequency- and temperature-dependent dielectric parameters (dielectric loss and dielectric constant) of the compounds have been carried out from 100 Hz to 100 kHz and from 50 to 500°C. Both of the dielectric parameters showed a decreasing trend with an increase in frequency. The highest dielectric loss value at a temperature of 500°C was obtained at ~4 for the undoped YSSO compound, and it reduced to ~1 after doping with x = 0.15 mol% of Eu³⁺ in YSSO: xEu compound. Impedance spectroscopy showed that the impedance values decreased with increasing frequency, resulting in an increase in electrical conductivity. The Nyquist plot indicated that the resistance contribution is dominant from the grain boundary effect and also, the NTCR behaviour of YSSO: xEu compounds was observed. The obtained low activation energy values (~0.04 eV) and low dielectric loss (~0.01–0.06) in high frequency across a broad temperature range indicate that the YSSO: xEu oxy-apatites can be used as paraelectric capacitors, electric power loss component, etc.