PHASE-COMPOSITION, OXYGEN-CONTENT, AND THERMAL-CONDUCTIVITY OF AIN(Y2O3) CERAMICS

An indirect method to determine the oxygen dissolved in AIN is devised for AIN(Y2O3) ceramics and then related to thermal conductivity. Dissolved oxygen is determined by first constructing the AIN-rich corner of the AIN-Y2O3-Al2O3 phase diagram (isothermal section). This is achieved by (1) measuring the total oxygen content and subtracting from it the oxygen in the Y2O3, resulting in a virtual alumina content; (2) placing the sample composition on the diagram; (3) determining the phases present by XRD for each sample; and (4) drawing phase boundaries which best agree with the phases present. The intersection of these tie lines through the sample location with the AIN-Al2O3 axis then gives the particular Al2O3 oxygen content dissolved in the AIN lattice. For the system AIN-Y2O3-Al2O3, it is shown that it is indeed this fraction of the total oxygen content that has a decisive limiting influence on thermal conductivity of dense, polyphase AIN ceramics.