Structure and Microwave Dielectric Properties of Ga ₂ O ₃ -Doped SrTiO ₃ –NdAlO ₃ Ceramics

The demand for advanced microwave dielectric ceramics for 5G base station filters drives the need for materials combining moderate permittivity, high quality factor ( Q × f ), and near-zero temperature stability (τ f ). This work investigates Ga 2 O 3 -doped SrTiO 3 –NdAlO 3 (ST-NA) ceramics. The optimal base composition (0.5ST-0.5NA) achieves ε r = 40.2, Q × f = 12,729 GHz, τ f = 5.89 ppm/°C. To further enhance the microwave dielectric performance, Ga 2 O 3 doping was introduced into the ST-NA ceramics. The substitution of Ga 3+ for Ti 4+ not only induces associated oxygen vacancy formation but also effectively suppressed the reduction of Ti 4+ to Ti 3+ during sintering, thereby reducing conduction loss, while the dielectric constant remained relatively stable. Consequently, 1.5% Ga 2 O 3 -doped ST-NA ceramic exhibited excellent overall microwave dielectric properties, with ε r = 40.7, Q × f = 21,441 GHz, τ f = 1.78 ppm/°C. These results demonstrate that Ga 2 O 3 -doped ST-NA ceramics are promising candidates for temperature-stable, low-loss microwave components in 5G and other high-frequency communication systems.