Effect of Sintering Additive La₂O₃ Content on Properties of Si₃N4-AlN Composite Ceramics Prepared by Hot-Pressing Sintering

Si3N4-AlN composite ceramics were prepared by hot-pressing sintering at 1 800 ℃ under 30 MPa for 1 h in nitrogen atmosphere with AlN and Si3N4 as raw materials and La2O3 as sintering additive. The effect of La2O3 content on sintering performance, bending strength, thermal conductivity and dielectric loss of the composite ceramies was investigated. The results show that with the increase of La2O3 content, the porosity of the ceramics decreased first and then reached a fixed value, the phase transformation Si3N4 from α to β was gradually completed and more lanthanum-melilites were found in the grain boundaries. With the increase of La2O3 content, bending strength of the composites decreased gradually, dielectric loss decreased first and then increased, while the thermal conductivity increased first and then decreased. When the La2O3 content was 4% the bending strength reached maximum 574 MPa. The lowest dielectric loss of 4.55×10-3 and highest thermal conductivity of 11.7 W·m-1·K-1 were obtained at a La2O3 content of 6%.