The influence of the valence electron concentration on the phase formation of the Ni2In-structure type for the example of ternary compounds Mn2Gasub(0.5)Assub(0.5)(m), Fe3GaAs and COsub(2Ga0.5)Assub(0.5)

The structures of the metastable phase Mn2Gasub(0.5)Assub(0.5) (m) and the stable phases Fe3GaAs and Co2Gasub(0.5)Assub(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. (orig.)