Abstract

QUINTERO, M. et al. X-ray diffraction analysis of stannite, wurtz-stannite and pseudo-cubic quaternary compounds by Rietveld method. Rev. mex. fis. [online]. 2014, vol.60, n.2, pp.168-175. ISSN 0035-001X.

Room temperature X-ray powder diffraction measurements were carried out on nine polycrystalline samples of the Cu₂B^II C^IVX₄ (B=Mn, or Fe, or Co; C=Si, or Ge, or Sn; X=S, or Se, or Te) magnetic semiconductor compounds. The diffraction patterns were used to show the equilibrium conditions and to derive crystalline parameter values. The results showed that four of these compounds have a tetragonal stannite structure with space group 142m(N° 121), two an orthorhombic wurtz-stannite structure with space group Pmn2₁(N° 31) and three of them an orthorhombic pseudo-cubic structure with space group F222 (N° 22). In each case, the structure was refined using the Rietveld method. When the obtained atomic parameter values for the tetragonal compounds were plotted as a function of molecular weight W, it was found that the values of the atomic positions, the cation-anion bond distances, tetragonal distortion and internal distortion of the compounds containing S and/or Se lay on different lines. Also, it was found that when the experimental points of the cation-anion bond distances d_Cu-VI, d_II-VI and d_IV-VI were plotted against the effective lattice parameter a_e = (V/N)^1/3, a linear variation of these distances with a_e was obtained. Values of the ionic energy gap C_i and homopolar energy gap E_h using the Phillips-Van Vechten scheme, with the present experimental crystallographic results as well as using the atomic data, were determined. It was found that the observed and predicted values of C_i and E_h lie on the same straight line.

Keywords : Magnetic semiconductors; crystal structure; X-ray powder diffraction; Rietveld refinement; crystal growth.