The effect of annealing process on the optical and microwave dielectric properties of transparent MgAl2O4 ceramics by spark plasma sintering

•Transparent MgAl2O4 ceramics were fabricated by using spark plasma sintering.•The effects of annealing temperature were studied by PALS and XPS.•The critical annealing temperature is 900 °C for the optical properties.•The concentration of oxygen vacancies decreased after annealed.•A certain annealing temperature is corresponding to the best microwave dielectric properties.

Transparent MgAl2O4 ceramics were fabricated by using spark plasma sintering (SPS). The effects of annealing temperature on the optical and microwave dielectric properties were investigated by positron annihilation technique and X-ray photoelectron spectroscopy (XPS). The results showed that the optimal annealing temperature for the optical property improvement was 900 °C and the in-line transmittance was improved to 74.9% at the wavelength of 550 nm. The further elevation of annealing temperature damaged the optical performance due to the combination of oxygen vacancies. The Q × f values of transparent MgAl2O4 ceramics were an overall increase from 800 °C to 1200 °C, but decreased at 1300 °C. It can be concluded that the annealing temperature plays an important role in the Q × f value, while a certain annealing temperature is corresponding to the best microwave dielectric property.