Resumen de X-ray diffraction analysis of stannite, wurtz-stannite and pseudo-cubic quaternary compounds by Rietveld method
M. Quintero, J. Marquina, E. Quintero, E. Moreno, S. Álvarez, C. Rincón, P. Grima, P. Bocaranda, D. Rivero, J. A. Henao, M.A. Macías
Room temperature X-ray powder diffraction measurements were carried out on nine polycrystalline samples of the Cu_(2)B^(II)C^(IV)X_(4)(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 drive crystalline parameter values. The results showed that four of these compounds have a tetragonal stannite structure with space group I42m(Nº 121), two an orthorhombic wurtz-stannite structure with space group Pmn2_(1)(Nº31) and three of them an orthorhombic pseudo-cubic structure with space group F222(Nº22). 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.
