Transparent polycrystalline MgAl2O4 ceramic fabricated by spark plasma sintering: Microwave dielectric and optical properties

The optical properties and microwave dielectric properties of transparent polycrystalline MgAl2O4 ceramics sintered by spark plasma sintering (SPS) through homemade nanosized MgAl2O4 powders at temperatures between 1250 °C and 1375 °C are discussed. The results indicate that, with increasing sintering temperatures, grain growth and densification occurred up to 1275 °C, and above 1350 °C, rapid grain and pore growth occurred. The in-line light transmission increases with the densification and decreases with the grain/pore growth, which can be as high as 70% at the wavelength of 550 nm and 82% at the wavelength of 2000 nm, respectively. As the sintering temperature increases, Q×f and dielectric constant εr values increase to maximum and then decrease respectively, while τf value is almost independent of the sintering temperatures and remains between −77 and −71 ppm/°C. The optimal microwave dielectric properties (εr=8.38, Q×f=54,000 GHz and τf=−74 ppm/°C) are achieved for transparent MgAl2O4 ceramics produced by spark plasma sintering at 1325 °C for 20 min.