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Title: The influence of the Jahn-Teller effect at Fe 2+ on the structure of chromite at high pressure

Abstract

The crystal structure of chromite FeCr 2O 4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch-Murnaghan equation of state (EoS) based on the P-V data gives: K 0 = 209 (13) GPa, K' = 4.0 (fixed), and V 0 = 588 (1) Å 3. The FeO 4 tetrahedra and CrO 6 octahedra are compressed isotropically with pressure with their Fe-O and Cr-O bond distances decreasing from 1.996 (6) to 1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe 2+ cation is more compressible than the octahedral site occupied by the Cr 3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K 0 = 147 (9) GPa, K' = 4.0 (fixed), V 0 = 4.07 (1) Å 3 and K 0 = 275 (24) GPa, K' = 4.0 (fixed), V 0 = 10.42 (2) Å 3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd-3more » m) to a tetragonal structure (space group I4 1/amd). At the phase transition boundary, the two Cr-O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr-O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5 o to 106.6 (7) o, which generates a 'stretched' tetrahedral geometry. It is proposed that the Jahn-Teller effect at the tetrahedrally coordinated Fe 2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn-Teller effect observed in this structure and its role in the pressure-induced phase transition.« less

Authors:
; ; ; ; ; ; ;  [1]
  1. CIW
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
NSFOTHERUNIVERSITYDOE - BASIC ENERGY SCIENCESNASA
OSTI Identifier:
1034958
Resource Type:
Journal Article
Journal Name:
Physics and Chemistry of Minerals
Additional Journal Information:
Journal Volume: 39; Journal Issue: (2) ; 2012; Journal ID: ISSN 0342-1791
Country of Publication:
United States
Language:
ENGLISH
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; AMBIENT TEMPERATURE; ATOMIC MODELS; BOND ANGLE; CATIONS; CHROMITES; COMPRESSION; CRYSTAL STRUCTURE; DEFORMATION; DIAMONDS; EQUATIONS OF STATE; IRON NITRATES; JAHN-TELLER EFFECT; MOLECULES; PRESSURE RANGE GIGA PA; SPINELS; X-RAY DIFFRACTION

Citation Formats

Kyono, Atsushi, Gramsch, Stephen A, Yamanaka, Takamitsu, Ikuta, Daijo, Ahart, Muhtar, Mysen, Bjørn O, Mao, Ho-kwang, Hemley, Russell J, and Tsukuba). The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure. United States: N. p., 2012. Web. doi:10.1007/s00269-011-0468-6.
Kyono, Atsushi, Gramsch, Stephen A, Yamanaka, Takamitsu, Ikuta, Daijo, Ahart, Muhtar, Mysen, Bjørn O, Mao, Ho-kwang, Hemley, Russell J, & Tsukuba). The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure. United States. doi:10.1007/s00269-011-0468-6.
Kyono, Atsushi, Gramsch, Stephen A, Yamanaka, Takamitsu, Ikuta, Daijo, Ahart, Muhtar, Mysen, Bjørn O, Mao, Ho-kwang, Hemley, Russell J, and Tsukuba). Thu . "The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure". United States. doi:10.1007/s00269-011-0468-6.
@article{osti_1034958,
title = {The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure},
author = {Kyono, Atsushi and Gramsch, Stephen A and Yamanaka, Takamitsu and Ikuta, Daijo and Ahart, Muhtar and Mysen, Bjørn O and Mao, Ho-kwang and Hemley, Russell J and Tsukuba)},
abstractNote = {The crystal structure of chromite FeCr2O4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch-Murnaghan equation of state (EoS) based on the P-V data gives: K0 = 209 (13) GPa, K' = 4.0 (fixed), and V0 = 588 (1) Å3. The FeO4 tetrahedra and CrO6 octahedra are compressed isotropically with pressure with their Fe-O and Cr-O bond distances decreasing from 1.996 (6) to 1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe2+ cation is more compressible than the octahedral site occupied by the Cr3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K0 = 147 (9) GPa, K' = 4.0 (fixed), V0 = 4.07 (1) Å3 and K0 = 275 (24) GPa, K' = 4.0 (fixed), V0 = 10.42 (2) Å3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd-3– m) to a tetragonal structure (space group I41/amd). At the phase transition boundary, the two Cr-O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr-O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5o to 106.6 (7)o, which generates a 'stretched' tetrahedral geometry. It is proposed that the Jahn-Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn-Teller effect observed in this structure and its role in the pressure-induced phase transition.},
doi = {10.1007/s00269-011-0468-6},
journal = {Physics and Chemistry of Minerals},
issn = {0342-1791},
number = (2) ; 2012,
volume = 39,
place = {United States},
year = {2012},
month = {3}
}