The Ti-rich biotite from graphite-bearing metapelitic xenoliths (El Joyazo – Spain) have been recently studied trough a multitechnical approach [1]. The study, combining several techniques, showed TiO2 content ranging from 4.5 to 4.9 wt% and a constant XFe = 0.67. According to the results of their investigations, Cesare et al. [1], suggest that titanium (as Ti4+) is logged only in octahedral site. The aim of the present work is the investigation both the oxidation state and the site partition of titanium accepting the main crystal chemical conclusion achieved by [1]. The following Ti-coordination polyhedra have been considered during XPS analysis: 4-fold coordination (tetrahedral), 5+1 coordination (distorted octahedral), 6-fold coordination (regular octahedral). In order to obtain the best fitting, the BE of the Ti4+ for the octahedral and tetrahedral coordination have been determined following the procedure in [2]. While the BE for Ti4+ in distorted octahedron (5+1) has been obtained by means of ab initio calculations [3]. The result of XPS investigation shows that Ti4+ populates both tetrahedral and octahedral sites. Taking in account the structural formula proposed by [1], we note that the entrance of Ti4+ in the tetrahedral site and of Al3+ in octahedral site, in the same amount, results in a both better balance of the substitution mechanisms and in a better m. a. n.’s agreement between EPMA and SCXRD dat

Ti-investigation by XPS of Biotite from Metapelites of El Joyazo (Spain)

MESTO, ERNESTO;
2005-01-01

Abstract

The Ti-rich biotite from graphite-bearing metapelitic xenoliths (El Joyazo – Spain) have been recently studied trough a multitechnical approach [1]. The study, combining several techniques, showed TiO2 content ranging from 4.5 to 4.9 wt% and a constant XFe = 0.67. According to the results of their investigations, Cesare et al. [1], suggest that titanium (as Ti4+) is logged only in octahedral site. The aim of the present work is the investigation both the oxidation state and the site partition of titanium accepting the main crystal chemical conclusion achieved by [1]. The following Ti-coordination polyhedra have been considered during XPS analysis: 4-fold coordination (tetrahedral), 5+1 coordination (distorted octahedral), 6-fold coordination (regular octahedral). In order to obtain the best fitting, the BE of the Ti4+ for the octahedral and tetrahedral coordination have been determined following the procedure in [2]. While the BE for Ti4+ in distorted octahedron (5+1) has been obtained by means of ab initio calculations [3]. The result of XPS investigation shows that Ti4+ populates both tetrahedral and octahedral sites. Taking in account the structural formula proposed by [1], we note that the entrance of Ti4+ in the tetrahedral site and of Al3+ in octahedral site, in the same amount, results in a both better balance of the substitution mechanisms and in a better m. a. n.’s agreement between EPMA and SCXRD dat
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11586/63166
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