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Resonance Raman study of the high‐pressure phase transition in chromium‐doped titanite, CaTiOSiO 4
Author(s) -
Heyns Anton M.,
Harden Peter M.,
Prinsloo Linda C.
Publication year - 2000
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/1097-4555(200008/09)31:8/9<837::aid-jrs601>3.0.co;2-3
Subject(s) - raman spectroscopy , titanite , phase transition , ion , octahedron , chromium , doping , materials science , softening , analytical chemistry (journal) , chemistry , crystallography , condensed matter physics , optics , metallurgy , composite material , physics , quartz , optoelectronics , organic chemistry , chromatography
Titanite, CaTiOSiO 4 , was doped with chromium and the resultant Cr 4+ ions, which replaced the Si 4+ ions in the lattice gave rise to resonance effects in the Raman spectra recorded with an argon ion laser. The resonance‐enhanced Raman bands of the Cr 4+ ions, and other bands, were used as a probe to investigate the pressure‐induced phase transition that occurs in CaTiOSiO 4 . This transition occurs at 3.0±0.2 GPa at ambient temperatures and involves a change in the symmetry from P2 1 /a to A2/a in the crystals. In the P2 1 /a‐phase, the Cr—O and Si—O bonds strengthen under compression, in contrast to the softening of the Ti—O bonds. This is due to the centering of the Ti ion in the octahedron and is caused by overbonding effects of titanium under high pressure. In the high‐pressure A 2/ a phase, considerable strengthening occurs in the Si—O bonds, exemplified by changes in the Grüneisen parameters of particularly the asymmetric stretching and bending modes, while the Ti—O stretching mode continues to soften. The pressure‐ and temperature‐induced phase transitions in titanite are compared and contrasted. Copyright © 2000 John Wiley & Sons, Ltd.