The phase relations in the Gd–Fe–Ga ternary system at 500 °C

The isothermal section (500 °C) of the phase diagram of the Gd–Fe–Ga ternary system was investigated by X-ray powder diffraction analysis. Eleven binary compounds, GdGa2, GdGa, Gd3Ga2, Gd5Ga3, GdFe2, GdFe3, Gd2Fe17, Fe3Ga, Fe6Ga5, Fe3Ga4 and FeGa3, have been confirmed. Two ternary compounds, GdFe5.3Ga6.7 and GdFe5Ga7, were found in this ternary system at 500 °C. The compound GdFe5.3Ga6.7 is orthorhombic ScFe6Ga6-type structure (space group Immm) with a = 0.8567 (9), b = 0.86960 (9) and c = 0.50782 (5) nm, while the compound GdFe5Ga7 is tetragonal ThMn12-type structure (space group I4/mmm) with a = 0.8651(1) and c = 0.50934 (6) nm. The isothermal section at 500 °C consists of 16 single-phase regions, 31 two-phase regions and 16 three-phase regions. The maximum solid solubilities of Ga in GdFe2, GdFe3, Gd2Fe17 are 9.2, 9.0, and 44.3 at.% respectively. The homogeneity range of GdGa2 is from 22 to 33.3 at.% Ga in Gd–Ga side but the solid solubility of Fe in this compound is very small. The homogeneity range of GdFe5Ga7 is from 53.8 to 59.2 at.% Ga. Very limited solid solutions were measured in the other compounds.