The Equilibrium Pressure of N2 over GaN

The equilibrium pressures of N2 over and Ga are not known. Values of the heat and entropy of formation of are proposed that give equilibrium N2 pressures as a function of temperature. Experiments reported in the literature lead to consistent upper and lower bounds to the calculated curve but do not define its position very well. We report the results of three different types of experiments, using in H2, which tighten the bounds to the equilibrium curve: the pressures at which could be seen to form from Ga were upper limits; the pressure of in the exiting gas stream after reaction with Ga gives a qualified upper limit; and of greatest importance, we believe, are the measurements of the pressures generated when H2 is passed over . These latter pressures are lower limits to the equilibrium curve and are believed to lie close to it. The experimental results are in agreement with the calculated equilibrium pressures of N2 over GaN and Ga obtained using the heat of formation of based on the measurements of Hahn and Juza, and Mah and the assumption that the entropy and heat capacity of are the same as those of .