• journal_title：European Journal of Mineralogy
• Contributor：Michail N. Taran ; Haruo Ohashi
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2012/0024-2220
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：24
• issue：5
• firstpage：823
• section：Articles

Optical absorption spectra of synthetic clinopyroxenes of NaVSi₂O₆, LiVSi₂O₆ and CaVAlSiO₆ composition consist of a high-energy absorption edge and two broad absorption bands ν₁ and ν₂ at around 15,000 cm⁻¹ and 22,000 cm⁻¹ caused by spin-allowed electronic transitions ³T_1g (³F) → ³T_2g (³F) and ³T_1g (³F) → ³T_1g (³P) of V³⁺ in octahedral M1-site of the clinopyroxene structure. In polarized spectra of NaVSi₂O₆ and LiVSi₂O₆ pyroxenes the relative intensities of the polarized components of ν₁- and ν₂-bands are rather different, revealing differences in the distortion of VO₆-octahedra in the two structures. In spite of a formal similarity to the absorption spectra of Cr³⁺ in Cr-bearing clinopyroxenes, the pressure-induced behaviour of the spin-allowed bands of V³⁺ in NaVSi₂O₆-pyroxene is noticeably different: although they also shift to higher energies as do the bands of Cr³⁺, the integral intensity of the ν₁-band remains nearly constant within uncertainty whereas that of the ν₂-band somewhat decreases, in contrast to Cr³⁺ for which the spin-allowed bands significantly decrease. Comparing with k_oct^loc-value of CrO₆-octahedron in NaCrSi₂O₆ kosmochlor, ~196 GPa, the VO₆-octahedron in NaVSi₂O₆ clinopyroxene structure is considerably softer, with k_oct^loc ≈ 163 GPa. The <V – O>distances derived from the optical absorption spectra can fairly well be approximated by a linear dependence. The Racah parameter B of V³⁺ evidently decreases with increasing pressure from ~554 cm⁻¹ at 10⁻⁴ GPa to 508 cm⁻¹ at 10.7 GPa, thus indicating that V – O bonds in the VO₆-octahedra become more covalent.