Caracterização estrutural, térmica e em altas pressões da solução sólida nanoestruturada SnS0.5Se0.5 sintetizada por moagem mecânica

Abstract

Through the high energy milling of the elemental high purity powders of tin, sulfur, and selenium for one hour, under inert atmosphere, was formed a sample composed exclusively of the nanostructured solid solution SnS0.5Se0.5 (Pnma). In 50 hours of milling, under the same conditions, were identified two phases SnS0.5Se0.5 (Pnma) and SnS (Cmcm). Occurs the destabilization of the solid solution SnS0.5Se0.5 (Pnma) above 200 0C incidentally promoting the oxidation and formation of other phases in the system. The interaction between the atoms of selenium and sulfur in the solid solution SnS0.5Se0.5 (Pnma) lead to disorder in the atomic structure which caused expansion in the volume of the unit cell, obtained from the Rietveld refinement of the diffraction patterns, in ambient conditions. In high pressure this effect is insignificant in the a axis, however causes disparities in the compressibility of the b and c axis on the SnS0.5Se0.5 (Pnma) structure leading to an almost isotropic behavior. Was observed in the solid solution SnS0.5Se0.5 a continuous phase transition from the space group Pnma to the Cmcm between 7.9 and 10.1 GPa, from 12.4 GPa onwards only the solid solution SnS0.5Se0.5 (Cmcm) makes itself present and it’s stable until 20 GPa. Considering theorical calculation, DFT, although the behavior of the lattice parameter a in function of pressure was virtually the same, for the parameters b and c was not. Whilst in the DFT calculation the most compressible axis was the correspondent to the lattice parameter c, and the less compressible was the one correspondent to the parameter b, in the data obtained experimentally the axis correspondent to the lattice parameter a was the most compressible because c was only slightly more compressible than b. This phenomenon occurs due to the elimination of the existing defects, occurring at the same time as the phase transition in SnS1-xSex that incidentally lead to lower efficiency in the extinction of the corrugated configuration along the c axis reducing its compressibility. Through the fitting with the equation of state Birch-Murnaghan 3rd was calculated the bulk modulus of the nanostructured solid solution SnS0.5Se0.5 in 30 GPa.