Einfluss der Valenzelektronenkonzentration auf die Bildung der Phasen vom Ni₂In-Strukturtyp am Beispiel der ternären Verbindungen Mn₂Ga_0.5As_0.5(m),Fe₃GaAs und Co₂Ga_0.5As_0.5

The structures of the metastable phase Mn₂Ga_0.5As_0.5 (m) and the stable phases Fe₃GaAs and Co₂Ga_0.5As_0.5 are isotypic with Ni₂In. X-ray powder diffraction data are reported. Lattice constants and macroscopic densities were measured in the entire range of homogeneity. Crystal chemical parameters of these ternary phases and of the quasi-homologous isovalent phases are compared and discussed from the point of view of the valence-electron concentration and of the number of atoms in the unit cell. It is concluded that the valence-electron concentration is a very important but not a sufficient energetic factor for the stability of phases with the Ni₂In structure.