Characterization of AlN-based ceramic composites for use as millimeter-wave susceptor materials at high temperature: Dielectric properties of AlN:Mo with 0.25 vol% to 4.0 vol% Mo from 25 to 550 °C

Microstructural analysis and bulk dielectric property analysis ( real and imaginary permittivity at 95 GHz) were performed at temperatures ranging from 25 to 550 degrees C for ceramic composites comprising a hot- pressed aluminum nitride matrix ( containing yttria and trace carbon as sintering additives) with molybdenum powder as a millimeter- wave radiation- absorbing additive. Loading percentages in the range of 0.25 vol% to 4.0 vol% Mo were characterized. For the temperature regime evaluated, the temperature- related changes in real and imaginary components of permittivity were found to be relatively modest compared with those driven by Mo loading. Energy- dispersive X- ray spectroscopic analysis of Mo grains and surrounding regions showed the presence of a mixed- phase layer, containing Mo2C, at the AlN- Mo interface. The Mo2C- containing mixed- phase layer, typically a few micrometers thick, surrounded the Mo grains. Further characterization of this mixed- phase layer is required to determine its contribution to the dielectric properties of the composite.