Síntese e caracterização estrutural da dupla perovsquita Ca2mnreo6

• Autor(a) principal: Santos, Emanuelle Zangerolame
• Data de Publicação: 2010
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/4140
• topic: Engenharia Mecânica; Raios X - Difração; 621

Ceramic materials with perovskite structure have attracted great scientific and technological interest in recent years. Many of them have interesting physical properties such as superconductivity, ferroelectricity and colossal magneto-resistance. A variant of the simple perovskite structure, the ordered double perovskite, also can grow in cubic (or lower) symmetry, with general formula A2B‘B‖O6, where the ion A (divalent cation) occupies the vertices of the cube while B‘ and B” (transition metal) are alternately at the center of the oxygen-octahedron. This work describes the synthesis and characterization of Ca2MnReO6ordered double perovskyte. It does that by marking out sintered procedures and the structural properties, which have been investigated by synchrotron x –ray powder diffraction, x –ray absorption spectroscopy measurements. The Ca2MnReO6 double perovskite has been prepared in polycrystalline form by using theencapsulated quartz tube method. The partial oxygen pressure inside the quartz tube revealed this to be a crucial synthesis parameter for the production of a single structural phase sample. This parameter was controlled using the ratio between ReO2and ReO3content and the filling factor parameter (ratio between mass and total inner volume of the quartz tube).The morphology and chemical composition was investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The crystal structure parameters were determined by analysis of the synchrotron high-resolution X-ray powder diffraction pattern. The analysis indicates that the sample is an ideal single-phase compound with a monoclinic crystal structure (space group nP12) with a=5.44445(2) Å; b=5.63957(3) Å; c=7.77524(3) Å; and β=90.18(1)º. Computer simulations were performed considering twocation valence configurations, namely, (i) Mn2+Re6+or (ii) Mn3+Re5+, for the Ca2MnReO6 compound. XANES analysis measurements indicated +2.3 for the average valence of Mn (a mixture of Mn+2 and Mn+3) and +5.7 for the effective valence of Re (an intermediate valence between Re+4(ReO2) and Re+6(ReO3)). As a summary, we concluded there is a mixed valence configuration for Mn and Re in Ca2MnReO6 , taken into account the oxygen content of 6.00.1 .