Thermal resistance of grain boundary interfaces in polycrystalline aluminum nitride

Polycristalline aluminium nitride exhibit poor thermal conductivity in comp arison with that of monocristalline nitride. This is due to microstructural features specific of ceramic materials such as impurities, secondary phase s or grain boundaries... In an attempt to understand the effect of grain bo undaries on the macroscopic conductivity of yttria doped polycristalline al uminium nitride, local thermal measurements were achieved on two materials of quite different microstructure. Thermal investigation was performed by m eans of photoreflectance microscopy, a photothermal variant which allows a spatial resolution of a few micrometers. The experimental results are discu ssed in terms of thermal discontinuities or thick interphases of poor therm al properties at the boundaries. They are also linked to grain boundaries m icrostructural features. Moreover, the induced effect of each thermal behav iour on the macroscopic conductivity evaluation is presented.