Phase Composition, Oxygen Content, and Thermal Conductivity of AIN(Y ₂ O ₃ ) Ceramics

Abstract

An indirect method to determine the oxygen dissolved in AIN is devised for AIN(Y 2 O 3 ) ceramics and then related to thermal conductivity. Dissolved oxygen is determined by first constructing the AIN‐rich corner of the AIN—Y 2 O 3 —Al 2 O 3 phase diagram (isothermal section). This is achieved by (1) measuring the total oxygen content and subtracting from it the oxygen in the Y 2 O 3 , 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—Al 2 O 3 axis then gives the particular Al 2 O 3 oxygen content dissolved in the AIN lattice. For the system AIN—Y 2 O 3 —Al 2 O 3 , 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.