Microwave dielectric and thermal properties of mixed rare earth ortho phosphate [REmixPO4]

A cost effective protocol to develop microwave substrate is proposed whereby a mixed rare earth orthophosphate [REMIXPO4] ceramic was prepared using a natural mixture of rare earth oxides, which is a byproduct derived from beach sand after thorium extraction. The Rietveld refinement of X-ray powder diffraction pattern confirms that the compound belongs to P21/n space group with monoclinic crystal symmetry. The scanning electron microscopy combined with energy dispersive X-ray analysis was performed to study the surface morphological characteristics. The ceramic sintered at 1250 °C showed a relative permittivity (εr) of 9.6 (at 13.5 GHz), high quality factor (Qu×f) of 45,200 GHz and a τf of −35 ppm/°C. The room temperature thermal conductivity of the sintered ceramic is 3.25 Wm−1 K−1 while the average coefficient of thermal expansion (CTE) is 7.3 ppm/°C.