Phase transformation and microwave dielectric properties of BiPO ₄ ceramics

Monazite-type compounds, BiPO₄ polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The low-temperature phase of BiPO₄ has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when it is heated above 600°C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950°C has good microwave dielectric properties; the relative dielectric constant (ε _r ) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ _f ) = - 79 ppm/ °C.