Relation between high thermal conductivity and dissolved-oxygen content in AlN ceramics fabricated by spark plasma sintering

AlN ceramics with small grain sizes were fabricated by spark plasma sintering (SPS) using Y2O3 as the sintering aid. The thermal conductivity of the ceramics increased with rising sintering temperature; the specimen sintered at 1850 °C exhibited a thermal conductivity of 163 W m−1 K−1, comparable to that of ceramics produced by pressureless sintering at the same temperature. The amount of oxygen dissolved in AlN was estimated from the lattice parameter c, and its relation with thermal resistivity was analyzed by Slack's plot. A higher sintering temperature enhanced the trapping effect of the sintering aid and reduced the oxygen content in the solid solution. In addition, SPS-prepared samples showed higher bending strength than those obtained by pressureless sintering (PLS). These findings demonstrate that the combined use of SPS and sintering aids suppresses grain growth and lowers the dissolved-oxygen level, resulting in AlN ceramics with both high thermal conductivity and bending strength.