|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
2 Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada
3 Illinois EPR Research Center, University of Illinois, Urbana, Illinois 61801, U.S.A.
Correspondence: * E-mail: yuanming.pan{at}usask.ca
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/geße = 1069.2(1) G and E/geße = 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.
This article has been cited by other articles:
|
|
 |
|
  S. M. Nokhrin, Y. Pan, and M. J. Nilges Electron paramagnetic resonance spectroscopic study of carbonate-bearing fluorapatite: New defect centers and constraints on the incorporation of carbonate ions in apatites American Mineralogist, August 1, 2006; 91(8-9): 1425 - 1431. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Pan, N. Chen, J. A. Weil, and M. J. Nilges Electron paramagnetic resonance spectroscopic study of synthetic fluorapatite: Part III. Structural characterization of sub-ppm-level Gd and Mn in minerals at W-band frequency American Mineralogist, October 1, 2002; 87(10): 1333 - 1341. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. Pan, M. E. Fleet, N. Chen, J. A. Weil, and M. J. Nilges SITE PREFERENCE OF Gd IN SYNTHETIC FLUORAPATITE BY SINGLE-CRYSTAL W-BAND EPR AND X-RAY REFINEMENT OF THE STRUCTURE: A COMPARATIVE STUDY Can Mineral, August 1, 2002; 40(4): 1103 - 1112. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. Pan and M. E. Fleet Compositions of the Apatite-Group Minerals: Substitution Mechanisms and Controlling Factors Reviews in Mineralogy and Geochemistry, January 1, 2002; 48(1): 13 - 49. [Full Text] [PDF]
|
|
|
|
|
|
G. A. Waychunas Apatite Luminescence Reviews in Mineralogy and Geochemistry, January 1, 2002; 48(1): 701 - 742. [Full Text] [PDF]
|
|
|
|
|
|
N. Chen, Y. Pan, and J. A. Weil Electron paramagnetic resonance spectroscopic study of synthetic fluorapatite: Part I. Local structural environment and substitution mechanism of Gd3+ at the Ca2 site American Mineralogist, January 1, 2002; 87(1): 37 - 46. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
