ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPIC STUDY OF SYNTHETIC FLUORAPATITE: PART II. GD3+ AT THE CA1 SITE, WITH A NEIGHBORING CA2 VACANCY

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dc.contributor.author Chen N.
dc.contributor.author Pan Y.
dc.contributor.author Weil J.A.
dc.contributor.author Nilges M.J.
dc.date.accessioned 2021-10-15T05:06:41Z
dc.date.available 2021-10-15T05:06:41Z
dc.date.issued 2002
dc.identifier https://elibrary.ru/item.asp?id=27877696
dc.identifier.citation American Mineralogist, 2002, 87, 1, 47-55
dc.identifier.issn 0003-004X
dc.identifier.uri https://repository.geologyscience.ru/handle/123456789/30708
dc.description.abstract A W-band (94 GHz) electron paramagnetic resonance (EPR) study of synthetic fluorapatite with 57 ± 4 ppm Gd has been made on single crystals at ~287 K. The spectra disclosed the presence of a previously unreported type of Gd3+ center denoted by “b” herein (S = 7/2), in addition to the Gd3+ center “a” assigned to the Ca2 site using the results of a previous X-band (9.5 GHz) EPR study (Chen et al. 2002). In particular, the single-crystal W-band EPR spectra from three orthogonal-rotation planes allowed determination of an appropriate spin-Hamiltonian for center “b,” including the spin terms of type BS (matrix g) and S2 (matrix D) and the parameters associated with the high-spin terms of type S4 and S6 as well as BS3 and BS5. Agreement between the observed and simulated single-crystal spectra confirmed the validity of the spin-Hamiltonian analysis. The principal values of the matrices g and D [e.g., D/geβe = 1069.2(1) G and E/geβe = 52.4(3) G] suggest a considerably distorted rhombic local environment for the Gd3+ ions in center “b.” The principal directions of D suggest that “b” corresponds to Gd3+ at the Ca1 site. This site assignment is supported by a pseudo-symmetry analysis of the term S4, i.e., approximate matching of the directions of the calculated pseudo-symmetry axes to the bond directions and face normals of the coordination polyhedron of the ideal Ca1 site. The data suggest that the incorporation of Gd3+ into the Ca1 site is achieved by a coupled substitution (2Gd3+ + □ ↔ 3Ca2+) involving a Ca2+ vacancy □ and that the vacancy is located at a next-nearest-neighbor Ca2 site, resulting in a Gd3+-- □ --- Gd3+ arrangement, with the cations well separated.
dc.title ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPIC STUDY OF SYNTHETIC FLUORAPATITE: PART II. GD3+ AT THE CA1 SITE, WITH A NEIGHBORING CA2 VACANCY
dc.type Статья


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