The system Ga-Ni: A new investigation of the Ga-rich part

A new version of the Ga-Ni phase diagram was established based on the investigation of ten samples in the Ga-rich part by DTA, powder X-ray diffraction and EPMA. Two significant differences compared to the last version of the phase diagram were discovered. The most Ga-rich compound Ga4Ni was not found as such. Instead the existence of Ga7Ni3, as already described earlier in literature, was confirmed. Furthermore, the peritectic reaction GaNi + L ? Ga3Ni2 was found at a temperature of 950 °C, which is more than 50 °C higher than the indicated literature value. At 80 at.% Ga, additional lines in the X-ray powder patterns, which were also reported in literature, suggest the presence of a further, possibly metastable Ga-rich phase. Although no single-crystal X-ray diffraction measurements could be performed, the Ga-rich phase could be characterized using a Ga5Pd type crystal structure including a refinement of the atomic parameters. The partial and integral enthalpies of mixing of liquid Ga-Ni alloys were determined at various temperatures (1031, 1134, 1246, 1261, 1321, 1388 °C) using a drop calorimetric technique. No significant temperature dependence of ?mixH could be observed. The minimum was found at 52 at.% Ni with a value of -35 kJ/mol.