9. Determination of Solubility of GaN in Ammonobasic Systems

In this study, the solubility of GaN in the ammonobasic MNH₂–GaN–NH₃ (M = Na, K) systems in the temperature range of 350–550 °C was studied. The target value for the ammonia filling degree was 45% and 55% for mineralizers NaNH₂ and KNH₂, respectively. The mineralizer concentration was varied at all temperatures from 1 M to 3 M, in respect to the liquid ammonia. It has been found that the solubility of GaN with NaNH₂ as a mineralizer increases slightly with increasing temperature in the range 400–600 °C, but is generally very low. A dependence of solubility on mineralizer concentration was not observed. An increase in the ammonia filling degree from 45% to 55% only slightly increased the solubility of GaN. The use of KNH₂ as a mineralizer brought an enormous increase in the solubility of GaN. Here, 7 times higher solubilities than those for NaNH₂ were observed. A retrograde solubility behavior of GaN in the temperature range 400–550 °C was determined for KNH₂ as a mineralizer. In the range of 350–400 °C the solubility showed a positive temperature dependence. The maximum solubility was reached at 400 °C. The solubility of GaN at 400 °C was found three times higher than at 550 °C.