Physics
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002pepi..129..145r&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 129, Issue 1-2, p. 145-151.
Physics
6
Scientific paper
The evolution with pressure of the unit-cell parameters brownmillerite (Ca2Fe2O5), a stoichiometric defect perovskite structure, has been determined to a maximum pressure of 9.46GPa, by single-crystal X-ray diffraction measurements at room temperature. Brownmillerite does not exhibit any phase transitions in this pressure range. A fit of a third-order Birch-Murnaghan equation-of-state to the P-V data yields values of KT0=127.0(5)GPa and K0'=5.99(13). Analysis of the unit-cell parameter data shows that the structure compresses anisotropically. Compressional moduli for the axes are Ka0=141(1)GPa, Kb0=118(3)GPa and Kc0=122.2(2)GPa, with Ka0'=8.9(3), Kb0'=6.2(6) and Kc0'=4. The stiffest direction (i.e. along a) coincides with the direction of the FeO4 tetrahedral chains. Comparison of these data with the elasticity systematics of Ca-perovskites shows that the presence of oxygen vacancies in the brownmillerite structure softens the structure by ~25% and that the ordering of vacancies in the perovskite structure increases the anisotropy of compression.
Angel Roger J.
Ross Nancy L.
Seifert Frank
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