Subsolidus phase relations of the Cu–Ga–N system

The subsolidus phase relations of the Cu–Ga–N system are studied by X-ray powder diffraction. The phase relations of the binary Cu–Ga system are checked firstly. θ-CuGa2 which belongs to the tetragonal system is determined to be a stoichiometric compound and its thermal expansion is measured by temperature-dependent X-ray powder diffraction from 93 to 523 K. The linear temperature dependences of the expansion coefficients along the a- and c-axis and volume coefficients are obtained, αa = (1.97349 − 3.84678 × 10−5T) × 10−5, αc = (2.00261 − 3.96007 × 10−5T) × 10−5 and αV = (6.01498 − 3.49098 × 10−4T) × 10−5, respectively. No ternary compound is found in the Cu–Ga–N system. Cu and its alloys could have some reaction with GaN under the present experimental condition.