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

Abstract The optical properties and microwave dielectric properties of transparent polycrystalline MgAl 2 O 4 ceramics sintered by spark plasma sintering (SPS) through homemade nanosized MgAl 2 O 4 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 e r values increase to maximum and then decrease respectively, while τ f value is almost independent of the sintering temperatures and remains between −77 and −71 ppm/°C. The optimal microwave dielectric properties ( e r =8.38, Q × f =54,000 GHz and τ f =−74 ppm/°C) are achieved for transparent MgAl 2 O 4 ceramics produced by spark plasma sintering at 1325 °C for 20 min.