Preparation and microwave dielectric properties of BPO4 ceramics with ultra-low dielectric constant

BPO4 ceramics with a cristobalite-like structure were prepared via solid-state sintering (SSS) and spark plasma sintering (SPS). Significant shrinkage and grain growth were observed with increasing the sintering temperature up to 1200 degrees C for SSS samples, while the highest relative density is only 74.6% because of the serious sublimation of BPO4, and the microwave dielectric properties of epsilon(r) = 3.38, Qf = 18,200 GHz and tau(f) = -42.8 ppm/degrees C were achieved at 14.6 GHz for SSS samples sintered at 1000 degrees C for 3 h. A much higher relative density of 92.7% was obtained in SPS sample (1000 degrees C/10 min) with epsilon(r) = 4.20, Qf = 4,000 GHz, and tau(f) = -20.7 ppm/degrees C. The Qf value increases by a factor of 6.9 and 5.9 with increasing frequency from 4.6 GHz to 14.6 GHz for SSS and SPS samples, respectively, which implies that the Qf value is dominated by extrinsic factors and has a huge improvement space. The corrected dielectric constant by porosity is only 4.65, indicating that BPO4 ceramic is a promising candidate as the microwave substrate material if the relative density and microstructure can be further improved.

Automated summary

The research on the performance of BPO4 ceramics prepared by solid-state sintering and spark plasma sintering shows that increasing the sintering temperature leads to significant shrinkage and grain growth, but also causes serious sublimation and low relative density issues for BPO4. Sintering temperature has a significant impact on the microwave dielectric properties of the material, with SPS samples having higher relative density but lower Qf value, each with their own advantages and disadvantages.