Crystal structure of the ordered Nb 10Ge 7 phase

Abstract

The structure of a new ordered phase, Nb 10Ge 7 (or Nb 5Ge 3Ge 0.5; trigonal), is described on the basis of electron microscopic and electron diffraction data. The new phase was found in a Nb Ge tape prepared by the coevaporation technique. The new structure can be derived from the hexagonal D8 8-structure of Nb 5Ge 3 by periodically inserting Ge-atoms at octahedral sites. The lattice parameters of this structure can be described as follows, using the lattice parameters of the D8 8-structure a= √3 ·a Nb 5Ge 3(D 88 and c=C Nb 5Ge 3(D 88) in hexagonal description. The grains of this phase are usually elongated along the c-direction. Structural data of the new phase: Nb 10Ge 7,trigonal, hP51, P 3¯2/ml,a= 1.337nm,c= 0.537nm,Z= 3,V Nb 10Ge 7 ≈ 3V Nb 5Ge 3(D 88) . The structure represents a new structure type with an ordered atom arrangement, intermediate between the Mn 5Si 3 type and the Ti 5Ga 4 type, in which the octahedral sites are only partly occupied.