High-temperature neutron diffraction of the AlN-Al2O3-Y2O3 system

The importance of aluminum nitride (AIN) stems from its application in microelectronics as a substrate material due to high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability, and chemical stability. Yttria (Y2O3) is the best additive for AIN sintering. AIN densifies by a liquid-phase mechanism, where the surface oxide, Al2O3, reacts with Y2O3 to form an Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is essential for optimizing the properties of AIN. The ternary phase diagram of the AIN-Al2O3-Y2O3 was developed by Gibbs energy minimization using interpolation procedures based on modeling the binary subsystems. This paper aims at testing the resultant understanding experimentally at selected compositions using in situ high-temperature neutron diffractometry. These experimental results agree with the thermodynamic calculations of AlN-Al2O3-Y2O3. The ternary phase diagram has been constructed for the first time in this work. High-temperature neutron diffractometry has permitted real time measurement of the reactions involved in this ternary system, especially to determine the temperature range for each reaction, which would have been difficult to establish by other means.