The crystal structure of La-doped Co40V60 compound

Crystal structure of the compounds Co40V60−2xLax has been investigated by means of X-ray powder diffraction (XRD). The compounds crystallize in the tetragonal σ phase structure with the space group P42/mnm and form a solid solution with a solubility limit of x = 9.52. The lattice parameters a, c and the unit cell volume V of the compounds decrease linearly with the La content. A structure model with a preferential substitution of La for V atoms on the 8j sites accompanied by the presence of vacancies on these sites is proposed for Co40V44La8. The proposal structure model gives a satisfactory fitting to the XRD data and a reasonable La content close to the nominal composition as well as a coincidence of the calculated density with the experimentally measured one. The preferential occupation of La atoms on the 8j site is discussed based on a consideration of geometric constrain and thermodynamics.