The crystal structure of La-doped Co40V60 compound

Abstract Crystal structure of the compounds Co 40 V 60−2 x La x has been investigated by means of X-ray powder diffraction (XRD). The compounds crystallize in the tetragonal σ phase structure with the space group P 4 2 / 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 Co 40 V 44 La 8 . 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.