Flux-grown Fe3+ -bearing spinel s.s.-hercynite solid-solution crystals, (Mg1-yFe2+ y)Al2O4 (0 < y ≤ 1), have been investigated by means of electron microprobe technique and Mössbauer and electronic spectroscopy. Obtained results show that different electronic processes cause intense optical absorption bands in the near-infrared spectral region. In addition to an electronic d-d transition in single-ion IVFe2+, observed at 5200 cm-1, intense and broad bands at 9500 and 14 500 cm-1 are assigned to exchange-coupled pair (ECP) and intervalence charge-transfer (IVCT) transitions in VIFe2+ VIFe3+ clusters, respectively. The net linear extinction coefficients of these bands (α) were calibrated against Fe2+ and Fe3+ concentrations and site distributions previously defined by combined microchemical, Mössbauer, and XRD structural refinement data. The following expressions were obtained: α5200 = 59 ± 4 [IVFe2+], α9500 = 189 ± 36 [VIFe2+][VIFe3+] and α14500 = 141 ± 25 [VIFe2+][VIFe3+], where α is measured in cm-1 and concentrations are expressed in mol l-1. The present results show that optical absorption spectroscopy may be used as a probe to obtain high spatial resolution (∅ ~ 10 μm) information on Fe2+ ordering as well as on Fe3+ concentrations in minerals belonging to the spinel group.
Influence of cation distribution on the optical absorption spectra of Fe3+-bearing spinel s.s.-hercynite crystals: Evidence for electron transitions in VIFe2+-VIFe3+ clusters / U., Halenius; H., Skogby; Andreozzi, Giovanni Battista. - In: PHYSICS AND CHEMISTRY OF MINERALS. - ISSN 0342-1791. - 29:5(2002), pp. 319-330. [10.1007/s00269-002-0240-z]
Influence of cation distribution on the optical absorption spectra of Fe3+-bearing spinel s.s.-hercynite crystals: Evidence for electron transitions in VIFe2+-VIFe3+ clusters
ANDREOZZI, Giovanni Battista
2002
Abstract
Flux-grown Fe3+ -bearing spinel s.s.-hercynite solid-solution crystals, (Mg1-yFe2+ y)Al2O4 (0 < y ≤ 1), have been investigated by means of electron microprobe technique and Mössbauer and electronic spectroscopy. Obtained results show that different electronic processes cause intense optical absorption bands in the near-infrared spectral region. In addition to an electronic d-d transition in single-ion IVFe2+, observed at 5200 cm-1, intense and broad bands at 9500 and 14 500 cm-1 are assigned to exchange-coupled pair (ECP) and intervalence charge-transfer (IVCT) transitions in VIFe2+ VIFe3+ clusters, respectively. The net linear extinction coefficients of these bands (α) were calibrated against Fe2+ and Fe3+ concentrations and site distributions previously defined by combined microchemical, Mössbauer, and XRD structural refinement data. The following expressions were obtained: α5200 = 59 ± 4 [IVFe2+], α9500 = 189 ± 36 [VIFe2+][VIFe3+] and α14500 = 141 ± 25 [VIFe2+][VIFe3+], where α is measured in cm-1 and concentrations are expressed in mol l-1. The present results show that optical absorption spectroscopy may be used as a probe to obtain high spatial resolution (∅ ~ 10 μm) information on Fe2+ ordering as well as on Fe3+ concentrations in minerals belonging to the spinel group.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.