ISSN:
1432-2021
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Abstract High-pressure electronic absorption spectra at room temperature and at pressures 10−4〈P[GPa]〈8 were measured in the spectral range 380〈λ[nm] 〈780(26218〉ν˜[cm−1]〉12820) on analysed single crystal slabs, about 20 μm thick, of Cr3+-bearing spinel (I), kyanite (II), corundum (III), pyrope (IV) and uvarovite (V) using DAC-cell techniques in combination with single-beam microscopespectrometry. Ligand field theoretical evaluation of the spectra yielded following results: (i) the octahedral crystal field parameter, 10DqCr3+[6], linearly shifts on increasing pressure to higher energies with slopes, (δ10DqCr3+[6]/δP), of 103.1 (I), 99.5 (II), 104.0 (III), 111.7 (IV) and 110.3 [cm−1/GPa] (V) (reliability parameters r≥0.92), (ii) The Racah-parameter BCr3+[6], reflecting the covalency of the Cr–O bonds, does not significantly change with pressure up to 8 GPa, in those cases where it could be evaluated from the spectra (III, IV, V). This result is contrary to the behaviour of BCr3+[6] with increasing temperature (Taran et al. 1994) and shows that P and T are not inversely correlated parameters with respect to BCr3+[6], a decrease of which reflects an increase in covalency. (iii) This result enabled to extract octahedral compression moduli, kCr3+[6], from the pressure slopes of 10DqCr3+[6]: 312+48 (I), 297+70 (II), 298+44 (III), 275+35 (IV), 257+32 GPa (V). Quotients kcr3+[6]/kbulk,phase are nearly the same (ca. 1.6) for I, II, IV and V but significantly lower (ca. 1.1) for III. Deviations between spectroscopically determined kCr3+[6] and published kAl[6], obtained by HP-XRD on ruby and pyrope, are interpreted by lattice strain induced by [Cr3+, Al3+−1][6] substitution.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002690050023
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