• journal_title：American Mineralogist
• Contributor：Taku Okada ; Toshiharu Narita ; Takaya Nagai ; Takamitsu Yamanaka
• Publisher：Mineralogical Society of America
• Date：2008-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2008.2490
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：93
• issue：1
• firstpage：39
• section：Articles

The Raman spectra of MgXO₃-ilmenites (X = Si, Ge, Ti) were recorded up to 773 K at ambient pressure and up to 20–30 GPa at room temperature. Temperature and pressure dependence of the force constant of X-O stretching bands revealed that the expansion and compression behavior of XO₆ octahedra differed in the three ilmenites. For SiO₆ and GeO₆ octahedra, the shorter Si-O or Ge-O bonds became more lengthened with temperature and more shortened with pressure than did the longer Si-O or Ge-O bonds. In contrast, for TiO₆ octahedra, the longer Ti-O bonds became more lengthened with temperature and more shortened with pressure than did the shorter Ti-O bonds. For SiO₆ and GeO₆ at high temperatures and TiO₆ at high pressures, the cation positions moved in the direction of the c axis and tended to approach the center of the octahedra, decreasing the distortion of XO₆. For SiO₆ and GeO₆ at high pressures and TiO₆ at high temperatures, the cations moved away from the center, increasing the distortion of XO₆. One of the anharmonic correction terms on isochoric specific heat was also elucidated. The anharmonic effects were related to the elastic Debye temperature of the three ilmenites.