Investigation of structural, morphological and dielectric properties of yttrium magnesium silicate oxyapatite doped with Gd³⁺ ions

The present paper reports the structural, morphological, impedance, conductivity, and dielectric properties of Y_8-xMg₂(SiO₄)₆O₂: xGd (YMSO: Gd) oxyapatite compounds. The co-precipitation method was employed to prepare the compounds. The structural analysis was done by XRD and the obtained pattern confirmed the hexagonal structure with space group p6₃/m (176). The average crystallite size calculated using Scherrer’s equation was found to be 31.08 nm. The crystallite size (D) ranges from 39.65 nm to 14.96 nm and volume (V) from 761.12 ų to 760.92 ų. Both the values of D and V decreased with the increase in content of Gd³⁺ ions (x mol%). The SEM micrographs at different magnifications showed the morphological pattern of the compound and the mean grain size was observed to be ~ 250 nm. The EDX spectrum confirmed the presence of all the initial raw materials which were taken for the preparation of the compound. The theoretical and experimental values of the atomic and weight percentages of the compounds are found within close range of each other. The FTIR spectroscopy was employed under optimized conditions to obtain transmittance spectra which determined the peaks at 651 ± 2 cm⁻¹ and 715 ± 2 cm⁻¹, corresponding to O-Si–O and Mg-O bonds respectively. A broad peak at 1230 ± 2 cm⁻¹ may be attributed to the characteristic peak of Si–O bonds. The peaks at 1628.75 ± 2 cm⁻¹ and 3443 ± 2 cm⁻¹ is of water and hydroxyl groups, respectively, present in the compounds. These peaks confirmed the presence of functional groups in the series of the synthesized compounds. With increasing frequency and temperature, the dielectric parameters were found to follow a decreasing trend, owing to a decrease in polarization. The lowest value of dielectric loss (= 5) was found for x = 0.20 mol% of Gd³⁺ ions. The complex impedance, conductivity and electric modulus analysis were carried out to investigate the dielectric relaxation, electrical conduction and charge transport mechanism of the prepared compounds in the frequency range of 10² Hz – 10² kHz and the temperature range of 50 °C – 500 °C. The a.c. conductivity was found to disperse in high frequency region and the average activation energy was estimated to be 0.17 eV using the Arrhenius equation.