X-ray powder diffraction and electron diffraction studies of the Ni1±yGe1−xPx system

The wide-range of non-stoichiometric NiAs-type solid solution Ni1±yGe1−xPx has been studied by means of X-ray powder and electron diffraction. The incommensurately modulated structure of Ni(Ge, P) has been found to exist over a wide compositional range which is limited by the end points ≈NiGe0.8P0.2 and NiGe0.3P0.7 so that the general stoichiometry might be referred to as NiGe1−xPx with 0.2⩽x⩽0.7. The modulation wave vector is of the type image and its modulus is strongly composition dependent. A possible interpretation is given as a “soft transition”, via an incommensurately modulated structure, between the MnP and the NiP structure types, based on the almost purely displacive origin of the distortion. Further, the crystal structures of Ni5Ge2P3 and Ni2GeP seem to be commensurate approximations of the incommensurate modulated structure of Ni(Ge, P).