Caracteriza????o estrutural, t??rmica e em altas press??es da solu????o s??lida nanoestruturada SnS0.5Se0.5 sintetizada por moagem mec??nica

Submitted by Larissa da Silva Marques (larissamarques.ufam@gmail.com) on 2019-03-13T11:15:41Z No. of bitstreams: 3 Larissa-Marques-Diss.pdf: 2804462 bytes, checksum: c7203345508b6fb4af3490382b326fe5 (MD5) Ata-scan.pdf: 844717 bytes, checksum: bfb80d6e99a0a69649079ca3a7db24d6 (MD5) autodeposito.pdf: 658839 bytes, checksum: c0f059292dcfa765ed7dc86aa8939d44 (MD5) Approved for entry into archive by PPGCEM Ci??ncia e Engenharia de Materiais (ppgcem@ufam.edu.br) on 2019-03-18T16:09:57Z (GMT) No. of bitstreams: 3 Larissa-Marques-Diss.pdf: 2804462 bytes, checksum: c7203345508b6fb4af3490382b326fe5 (MD5) Ata-scan.pdf: 844717 bytes, checksum: bfb80d6e99a0a69649079ca3a7db24d6 (MD5) autodeposito.pdf: 658839 bytes, checksum: c0f059292dcfa765ed7dc86aa8939d44 (MD5) Approved for entry into archive by Divis??o de Documenta????o/BC Biblioteca Central (ddbc@ufam.edu.br) on 2019-03-18T17:52:12Z (GMT) No. of bitstreams: 3 Larissa-Marques-Diss.pdf: 2804462 bytes, checksum: c7203345508b6fb4af3490382b326fe5 (MD5) Ata-scan.pdf: 844717 bytes, checksum: bfb80d6e99a0a69649079ca3a7db24d6 (MD5) autodeposito.pdf: 658839 bytes, checksum: c0f059292dcfa765ed7dc86aa8939d44 (MD5) Made available in DSpace on 2019-03-18T17:52:12Z (GMT). No. of bitstreams: 3 Larissa-Marques-Diss.pdf: 2804462 bytes, checksum: c7203345508b6fb4af3490382b326fe5 (MD5) Ata-scan.pdf: 844717 bytes, checksum: bfb80d6e99a0a69649079ca3a7db24d6 (MD5) autodeposito.pdf: 658839 bytes, checksum: c0f059292dcfa765ed7dc86aa8939d44 (MD5) Previous issue date: 2019-02-26 CAPES - Coordena????o de Aperfei??oamento de Pessoal de N??vel Superior 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. A partir da moagem de alta energia dos p??s elementares de alta pureza de estanho, enxofre e sel??nio durante uma hora, sob atmosfera inerte, foi formada a amostra composta exclusivamente da solu????o s??lida SnS0.5Se0.5 (Pnma) nanoestruturada. Em cinquenta horas de moagem, nas mesmas condi????es, foram identificadas as fases SnS0.5Se0.5 (Pnma) e SnS (Cmcm). Ocorre a desestabiliza????o da solu????o s??lida SnS0.5Se0.5 (Pnma) a partir de 200 0C incidentalmente promovendo oxida????o e forma????o de outras fases do sistema. A intera????o entre os ??tomos de sel??nio e enxofre na solu????o s??lida SnS0.5Se0.5 (Pnma) levou a desordem da estrutura at??mica o que causou a expans??o do volume da c??lula unit??ria em condi????es ambiente. Em altas press??es esse efeito ?? desprez??vel no eixo correspondente ao par??metro de rede a, entretanto causa disparidades na compressibilidade dos correspondentes aos eixos b e c da estrutura da solu????o s??lida SnS0.5Se0.5 (Pnma) levando a um comportamento pr??ximo do isotr??pico. Foi observada na solu????o s??lida SnS0.5Se0.5 a transi????o de fase cont??nua do grupo espacial Pnma para o Cmcm entre 7.9 e 10.1 GPa, a partir de 12.4 GPa somente a solu????o s??lida SnS0.5Se0.5 (Cmcm) se faz presente e ?? est??vel at?? 20 GPa. Considerando os c??lculos te??ricos, DFT, em compara????o com os valores obtidos do refinamento Rietveld, embora o comportamento do par??metro de rede a em fun????o da press??o tenha sido virtualmente o mesmo, os par??metros b e c n??o o foram. Enquanto nos c??lculos de DFT o eixo mais compress??vel foi o correspondente ao par??metro de rede c e o menos compress??vel o correspondente ao b, nos dados obtidos experimentalmente o eixo a foi o mais compress??vel pois c se mostrou apenas ligeiramente mais compress??vel que b. Esse fen??meno ocorre devido a elimina????o de defeitos presentes, que ocorre ao mesmo tempo da transi????o de fase no SnS1-xSex que incidentalmente causa perda de efici??ncia na extin????o da configura????o de zigue-zague no eixo c reduzindo sua compressibilidade. Atrav??s do ajuste pela equa????o de estado Birch-Murnaghan de terceira ordem foi calculado o m??dulo de bulk da solu????o s??lida a SnS0.5Se0.5 nanoestruturada em 30 GPa.