Potential use of only YbO in producing dense SiN ceramics with high thermal conductivity by gas pressure sintering.

YbO is an efficient sintering additive for enhancing not only thermal conductivity but also the high-temperature mechanical properties of SiN ceramics. Here we report the fabrication of dense SiN ceramics with high thermal conductivity by the gas pressure sintering of α-SiN powder compacts, using only YbO as an additive, at 1900 °C under a nitrogen pressure of 1 MPa. The effects of YbO content, sample packing condition and sintering time on the densification, microstructure and thermal conductivity were investigated. Curves of the density plotted against the YbO content exhibited a characteristic '' shape with a local minimum at 3 mol% YbO and nearly complete densification below and above this concentration. The effects of the sample packing condition on the densification, microstructure and thermal conductivity strongly depended on the YbO content. The embedded condition led to more complete densification but also to a decrease in thermal conductivity from 119 to 94 W m K upon 1 mol% YbO addition. The sample packing condition had little effect on the density and thermal conductivity (102-106 W m K) at 7 mol% YbO. The thermal conductivity value was strongly related to the microstructure.