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
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Abstract
Room-temperature, single-crystal W-band (~94 GHz) electron paramagnetic resonance (EPR) spectra of a flux-grown fluorapatite (AP30-0) containing 0.8(1) ppm Gd and 0.9 ppm Mn disclose the presence of two even-isotope Gd3+ centers (electron spin number S = 7/2 and nuclear spin number I = 0) and a 55Mn2+ center (S = I = 5/2). The relative abundance of the two Gd3+ centers (corresponding to recently established centers “a” and “b” containing Gd3+ ions at the Ca2 and Ca1 sites, respectively) in AP30-0 has been estimated to be 0.20, indicating that “a” in this sample arises from the presence of ~0.2 ppm Gd at the Ca2 site. In addition, high-resolution W-band spectra of this sample at ~120 and ~77 K disclose the 155Gd and 157Gd spectra of “a,” in which these isotopes (I = 3/ 2) are only ~0.02 ppm in abundance. To the best of our knowledge, this is the first-ever demonstration of structural characterization of sub-ppm-level trace elements in minerals and their synthetic analogs. Moreover, the fact that the Gd3+ and 55Mn2+ centers in AP30-0 are detected despite the multiplicity of lines arising from their complex fine structures, hyperfine structures, and magneticsite splittings, suggests that the W-band EPR technique is potentially capable of characterizing trace elements with a single unpaired electron (S = 1/2) and zero nuclear spin (I = 0) at even lower concentrations.
The spin-Hamiltonian parameters of the 55Mn2+ center, including matrices g, D, A, and P, and high-spin term of type S4, have been determined by optimization using the single-crystal W-band EPR spectra of a Gd-doped fluorapatite containing 3.0(4) ppm Mn. The principal-axis directions of D and the pseudo-symmetry axes calculated from the S4 parameters confirm that this center corresponds to occupancy of 55Mn2+ ions at the Ca1 site. Also, the optimized parameters suggest that the Mn2+-substituted Ca1 site in the flux-grown fluorapatite has rhombic (i.e., triclinic) local symmetry [e.g., D/geβe = 436.2(6) G, E/geβe = 1.1(1) G], slightly different from the trigonal symmetry of the ideal Ca1 site.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Atomic-scale observations of franckeite surface morphology
- Surface control vs. diffusion control during calcite dissolution: Dependence of step-edge velocity upon solution pH
- First-principles calculation of the infrared spectrum of lizardite
- Hard-mode infrared spectroscopy of perovskites across the CaTiO3-SrTiO3 solid solution
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- Evolution of local electronic structure in alabandite and niningerite solid solutions [(Mn,Fe)S, (Mg,Mn)S, (Mg,Fe)S] using sulfur K- and L-edge XANES spectroscopy
- 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
- Experimental determination of the equilibria: rutile + magnesite = geikielite + CO2 and zircon + 2 magnesite = baddeleyite + forsterite + 2 CO2
- Symplectites derived from metastable phases in martian basaltic meteorites
- Copper speciation in vapor-phase fluid inclusions from the Mole Granite, Australia
- Trace-element partitioning between vacancy-rich eclogitic clinopyroxene and silicate melt
- Fluorite particles inducing butterfly aggregates of incipient microperthite in alkali feldspar from a syenite, the Patagonian Andes, southern Chile
- Thermal stability and spectroscopic studies of zemkorite: A carbonate from the Venkatampalle kimberlite of southern India
- Temperatures from triple-junction angles in sulfides
- Experimental determination of calcite solubility in H2O-NaCl solutions at deep crust/ upper mantle pressures and temperatures: Implications for metasomatic processes in shear zones
- Compressibility of stottite, FeGe(OH)6: An octahedral framework with protonated O atoms
- High-pressure behavior of bikitaite: An integrated theoretical and experimental approach
- Raman spectroscopic study of H2O in bikitaite: “One-dimensional ice”
- Hydrogen, lithium, and boron in mantle-derived olivine: The role of coupled substitutions
- Crystal chemistry of three tourmalines by SREF, EMPA, and SIMS
- Revised structure models for antigorite: An HRTEM study
- The structure of Mn-rich tuperssuatsiaite: A palygorskite-related mineral
- Single-crystal structure refinements and crystal chemistry of synthetic trioctahedral micas KM3(Al3+,Si4+)4O10(OH)2, where M = Ni2+, Mg2+, Co2+, Fe2+, or Al3+
- SIMS matrix effects in the analysis of light elements in silicate minerals: Comparison with SREF and EMPA data
- Letters. Equation of state of Al-bearing stishovite to 40 GPa at 300 K
- Order parameter behavior at the structural phase transition in cummingtonite from Mössbauer spectroscopy
- Deciphering Ni sequestration in soil ferromanganese nodules by combining X-ray fluorescence, absorption, and diffraction at micrometer scales of resolution
- Use of the spindle stage for orientation of single crystals for microXAS: Isotropy and anisotropy in Fe-XANES spectra
- A technique for mounting and polishing melt inclusions in small (<1 mm) crystals
