A Defect Perspective on High Thermal Conductivity Al ₂ O ₃ –TiO ₂ Dielectric Ceramics

ABSTRACT

The development of high‐power millimeter‐wave technology introduces new requirements on microwave dielectric ceramics. In addition to lower dielectric loss, higher thermal conductivity is also needed to meet heat dissipation demands. Developing high‐thermal‐conductivity microwave dielectric ceramics with larger relative permittivity ( ε _r ) would facilitate the miniaturization of high‐power devices. Adding TiO ₂ to the α‐Al ₂ O ₃ matrix can adjust the temperature coefficient of resonant frequency ( τ _f ) to near zero while increasing ε _r , making it an effective approach to obtain high thermal conductivity and low‐loss microwave dielectric ceramics. However, systematic defect analysis of the Al ₂ O ₃ –TiO ₂ composition is still lacking. This work investigates the dielectric and thermal properties of the Al ₂ O ₃ –TiO ₂ composition from a defect perspective. By combining low‐frequency dielectric spectra with thermally stimulated depolarization current (TSDC) techniques, it was found that the solid solution of Al ³⁺ in the rutile TiO ₂ phase suppresses the activity of defects such as oxygen vacancies. However, the introduction of Ti ⁴⁺ into the Al ₂ O ₃ phase introduces aluminum vacancies (), which cause anharmonic lattice vibrations and phonon scattering, adversely affecting the properties. The results indicate that improving sintering characteristics and further limiting the defect response of the TiO ₂ phase are beneficial for developing high‐thermal‐conductivity microwave dielectric ceramics with higher ε _r . The defect analysis presented in this work provides valuable guidance for the synergistic regulation of dielectric and thermal properties of microwave dielectric ceramics intended for high‐power millimeter‐wave applications.