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.
© 2001-2024 Fundación Dialnet · Todos los derechos reservados