Análise da valência do Mn e Re nos compostos cerâmicos Ca2MnReO6 e Ca1,9Y0,1 MnReO6

• Ano de defesa: 2014
• Autor(a) principal: Cavichini, Arthur Sant'Ana
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Mestrado em Engenharia Mecânica; Centro Tecnológico; UFES; Programa de Pós-Graduação em Engenharia Mecânica
• Palavras-chave em Português: Double perovskites; X-ray absorption spectroscopy; Manganese; Rhenium; Bond valence mode; Perovskitas duplas; Modelo de valência de ligação; Espectroscopia de raio X; Manganês; Rênio; Valencia (Quimica teorica); Engenharia Mecânica; 621
• Link de acesso: http://repositorio.ufes.br/handle/10/9770

In this work the analysis of the valences of the rhenium and manganese was undertaken in cera-mic compounds Ca2MnReO6and Ca1.9Y0.1MnReO6using the model of valence bond. For thecalculations of distances got bonds were used by Rietveld refinement from diffraction patternsof X-rays were considered that both sites have mixed valence. The calculations for the valencemodel were performed using parameters taken from the literature. For the calculations of Re6+,was proposed parameter0= 1.93Å and for Re5+the parameters0= 1.90Å and0= 1.92Å. The results valence that best set were used to calculate the occupation factor of Re6+andRe5+at the site of rhenium, and Mn2+and Mn3+in site of manganese, as well as for calcula-ting the average valence at each site. These results were compared with the results obtained byanalyzing the valence of X-ray absorption on Mn K edge and Re L3edge. After comparison, itwas concluded that the valences of Mn and Re presents in ceramic Ca2MnReO6are+2.3±0.3and+5.6±0.3with occupation factors of68%of Mn2+ions, and32%of Mn3+ions, and61%of Re6+ion and39%of Re5+ions. The results for compound Ca1.9Y0.1MnReO6to the valencesof the rhenium were few contradictory, which led us to review the results obtained by X-ray ab-sorption. Upon review, we conclude that the valence that best fits the compound is+2.2±0.3for Mn and+5.2±0.3for Re, shown a occupancy of80%of Mn2+and20%of Mn3+on thesite of manganese, and occupancy of25%to Re6+and75%to Re5+to the rhenium site