The effect of doping with nano-MgO and co-doping with nano-MgO–Gd2O3 on the densification behavior, mechanical
properties, and dielectric behavior of alumina was evaluated. Magnesium oxide-doped alumina nanoparticles
were prepared by the sol-gel method with varying nano-MgO ratios (5, 6, and 7 mass %). Alumina
samples containing 7 mass % MgO showed the highest densification and exhibited the greatest mechanical
strength due to reduced porosity (3.22 % for 1750 °C). The doping of alumina with nano-MgO also improved the
breakdown voltage and resistivity. Co-doping of alumina also enhanced the densification and mechanical
properties of sintered samples. The sample co-doped with a low content of nano-MgO–Gd2O3 (7 and 1 mass %,
respectively) and sintered at 1750 °C for 1 h displayed the best properties among the studied samples. They
exhibited the best electrical properties, with the highest breakdown voltage and resistivity, and the lowest
permittivity and dielectric loss.