Incongruent melting of gallium nitride at 7.5 GPa

Melting of GaN was studied at 7.5 GPa and 2300–2400 °C, using a split-sphere multi-anvil apparatus (BARS). Diamond synthesis from graphite in CaCO3–C system and platinum melting were used as reference points for HPHT cell calibration. The initial samples of GaN were placed into boron nitride or graphite ampoules. No quench glass or quench crystals of GaN have been established. The incongruent GaN melting in the part of the samples at 2300 °C and in all samples at 2400 °C was fixed. Metallic gallium and gallium nitride as well as metallic gallium, gallium nitride and gallium oxide were observed in boron nitride and graphite ampoules, respectively. Results of the experiment indicate that the congruent melting of gallium nitride would occur at pressures > 7.5 GPa.