Synchrotron radiation XANES spectroscopy of Ti in minerals: Effects of Ti bonding distances, Ti valence, and site geometry on absorption edge structure

Journal Article · · American Mineralogist; (USA)

OSTI ID:5152935

Waychunas, G A ^[1]

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1. Stanford Univ., CA (USA)

The near K-edge X-ray absorption spectra of Ti in a suite of silicate and oxide minerals have been examined in an effort to improve Ti characterization in solids. The spectra consist of electronic excitations, occurring in the pre-edge region, and multiple scattering resonances on the side and top of the edge. The pre-edge features are insensitive to Ti-O bond length, but are sensitive to valence, occurring about 2.0 eV lower in energy in Ti{sup 3+} samples. The second pre-edge feature is also sensitive to octahedral site distortion and to the presence of tetrahedral Ti{sup 4+} owing to intensification created by d-p orbital mixing. The multiple scattering features shift to lower energy as Ti-O bond length increases and also change in number, intensity, and energy in response to varying ligand symmetry. Analysis of these spectral features suggests that tetrahedral Ti{sup 4+} probably occurs only at very small concentration levels in silicates, even when the total Si{sup 4+} and Al{sup 3+} concentration is well below that necessary to fill available tetrahedral sites, as in the melanite-schlorlomite garnets. The levels of Ti{sup 3+} are more difficult to determine because of an apparent sensitivity of the pre-edge Ti{sup 4+} features to bulk chemistry. However, the overall results are consistent with only small amounts of Ti{sup 3+}, even in samples from localities where other analyses (wet chemical and Moessbauer) have indicated significant Ti{sup 3+}.

• OSTI ID: 5152935
• Journal Information: American Mineralogist; (USA), Vol. 72:1-2; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
SILICATE MINERALS
STRUCTURAL CHEMICAL ANALYSIS
TITANIUM COMPOUNDS
ABSORPTION SPECTRA
BINDING ENERGY
BOND LENGTHS
CHEMICAL BONDS
CRYSTAL LATTICES
GEOCHEMISTRY
VALENCE
CHEMISTRY
CRYSTAL STRUCTURE
DIMENSIONS
ENERGY
LENGTH
MINERALS
SPECTRA
TRANSITION ELEMENT COMPOUNDS
580000* - Geosciences