Effects of two-step sintering on thermal and mechanical properties of aluminum nitride ceramics by impedance spectroscopy analysis

The effects of two-step sintering on the microstructure, mechanical and thermal properties of aluminum nitride ceramics with Yb2O3 and YbF3 additives were investigated. AIN samples prepared using different sintering methods achieved almost full density with the addition of Yb2O3-YbF3. Compared with the one-step sintering, the grain sizes of AIN ceramics prepared by the two-step sintering were limited, and the higher flexural strength and the larger thermal conductivity were obtained. Moreover, the electrochemical impedance spectroscopy of AIN ceramic was associated with thermal conductivity by analyzing the defects and impurities in AIN ceramics. The fitting grain resistance and the activation energy for the grain revealed the lower concentrations of aluminum vacancy in the two-step sintered AIN ceramics, which resulted in the higher thermal conductivity. Thus, mechanical and thermal properties for AIN ceramics were improved with Yb2O3 and YbF3 additives sintered using two-step regimes.