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1587292 
Journal Article 
The stability and equation of state for the cotunnite phase of TiO2 up to 70 GPa 
Nishio-Hamane, D; Shimizu, Asa; Nakahira, R; Niwa, Ken; Sano-Furukawa, A; Okada, T; Yagi, T; Kikegawa, T 
2010 
1 
Physics and Chemistry of Minerals
ISSN: 0342-1791 
37 
3 
129-136 
WOS:000274853700001 
The stability and equation of state for the cotunnite phase
in TiO2 were investigated up to a pressure of about 70 GPa by high-pressure in situ X-ray
diffraction measurements using a laser-heated diamond anvil cell. The transition sequence under
high pressure was rutile -> alpha-PbO2 phase -> baddeleyite phase -> OI phase -> cotunnite phase
with increasing pressure. The cotunnite phase was the most stable phase at pressures from 40 GPa
to at least 70 GPa. The equation of state parameters for the cotunnite phase were established on
the platinum scale using the volume data at pressures of 37-68 GPa after laser annealing, in
which the St value, an indicator of the magnitude of the uniaxial stress component in the
samples, indicates that these measurements were performed under quasi-hydrostatic conditions. The
third-order Birch-Murnaghan equation of state at K (0)' = 4.25 yields V (0) = 15.14(5) cm(3)/mol
and K (0) = 294(9), and the second-order Birch-Murnaghan equation of state yields V (0) = 15.11
(5) cm(3)/mol and K (0) = 306(9). Therefore, we conclude that the bulk modulus for the cotunnite
phase is not comparable to that of diamond. 
TiO2; Cotunnite; Fluorite; Phase relation; Equation of state; High pressure