A Fe-57 Mossbauer spectroscopic study of sogdianite: an example of a symmetric electric field gradient around Fe3+

作者：Geiger Charles A^*; Grodzicki Michael

来源：Physics and Chemistry of Minerals, 2012, 39(1): 73-78.

DOI：10.1007/s00269-011-0461-0

• Sogdianite
• Ring silicates
• Mossbauer spectroscopy
• Electronic structure calculations
• Electric field gradient
• Quadrupole splitting
• Iron site distortion

Sogdianite, a double-ring silicate of composition (Zr0.76Ti0.384+Fe0.733+Al0.13)(Sigma=2) (square Na-1.15(0.85))(Sigma=2)K[Li3Si12 O-30] from Dara-i-Pioz, Tadjikistan, was studied by the combined application of Fe-57 Mossbauer spectroscopy and electronic structure calculations. The Mossbauer spectrum confirms published microprobe and X-ray single-crystal diffraction results that indicate that Fe3+ is located at the octahedral A-site and that no Fe2+ is present. Both the measured and calculated quadrupole splitting, Delta E-Q, for Fe3+ are virtually 0 mm s(-1). Such a value is unusually small for a silicate and it is the same as the Delta E-Q value for Fe3+ in structurally related sugilite. This result is traced back to the nearly regular octahedral coordination geometry corresponding to a very symmetric electric field gradient around Fe3+. A crystal chemical interpretation for the regular octahedral geometry and the resulting low DEQ value for Fe3+ in the Mossbauer spectrum of sogdianite is that structural strain is largely %26quot;taken up%26quot; by weak Li-O bonds permitting highly distorted LiO4 tetrahedra. Weak Li-O bonding allows the edge-shared more strongly bonded Fe3+O6 octahedra to remain regular in geometry. This may be a typical property for all double-ring silicates with tetrahedrally coordinated Li.

• 出版日期2012-1