THERMOPHYSICAL PROPERTIES OF SAPPHIRE, ALN AND MGAL2O4 DOWN TO 70-K

Well characterized sapphire, aluminium nitride and magnesium aluminium spinel have been used for the determination of their specific heat, thermal expansion and thermal conductivity (thermal diffusivity). The results of specific heat and thermal expansion follow known relationships for these properties. The thermal conductivity (data at 80 K Hemex sapphire perpendicular to to c-axis 2.5 W/cm K; AIN SHAPAL at 100 K 2.1 W/cm K; MgAl2O4 single crystal at 100 K 0.82 W/cm K) is discussed taking into account point defects as well as dislocations and grain boundary scattering of phonons for the polycrystalline aluminium oxide. Following this interpretation maximum values for the thermal conductivity as 5.0 W/cm K (sapphire), and 1.1 W/cm K (MgAl2O4) are indicated.