Structure, bonding, and geochemistry of xenon at high pressures

Science

Volumn 277, Issue 5328, 1997, Pages 930-933

  Caldwell, Wendel A ^a   Nguyen, Jeffrey H ^a   Pfrommer, Bernd G ^a   Mauri, Francesco ^a   Louie, Steven G ^a   Jeanloz, Raymond ^a  

^a NONE

Author keywords

[No Author keywords available]

Indexed keywords

XENON;

CORE; GEOCHEMISTRY; HIGH PRESSURE; XENON;

ARTICLE; CONFORMATIONAL TRANSITION; CONTROLLED STUDY; HIGH TEMPERATURE; HYPERBARISM; PRIORITY JOURNAL; QUANTUM MECHANICS;

EID: 0030862903     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.277.5328.930     Document Type: Article

References (38)

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24. 2Fe, ABC stacking being obtained with, respectively, two layers of Fe and one of Xe or two of Xe and one of Fe (space group P3m1). To find the minimum enthalpies, we used a quasi-Newton method to relax the internal coordinates and the unit-cell shapes of all structures for a given pressure [B. G. Pfrommer, M. Côté, S. G. Louie, M. L. Cohen, J. Comp. Phys. 131, 233 (1997)).
25. 2Fe, ABC stacking being obtained with, respectively, two layers of Fe and one of Xe or two of Xe and one of Fe (space group P3m1). To find the minimum enthalpies, we used a quasi-Newton method to relax the internal coordinates and the unit-cell shapes of all structures for a given pressure [B. G. Pfrommer, M. Côté, S. G. Louie, M. L. Cohen, J. Comp. Phys. 131, 233 (1997)).
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31. o′ for the two phases are within mutual uncertainties and are in close agreement with previous determinations [K. Asaumi, Phys. Rev. B 29, 7026 (1984)].
32. Experimentally, we find evidence for a topotactic relation between the two phases, which suggests a martensitic or "military" type transformation [J. W. Christian, The Theory of Transformations in Metals and Alloys, Part I (Pergamon, New York, ed. 2, 1975)]. The (111) peak of the fcc phase and the (002) peak of the hcp phase appear at the same d spacing, which implies identical orientations for the close-packed planes in the two structures [A. F. Schuch, R. L. Mills, D. A. Depatie, Phys. Rev. 165, 1032 (1968)]. A similar geometrical relation explains why three other hcp peaks, (004), (112), and (110), are also coincident with the (222), (311), and (220) fcc peaks. It is possible that the detailed transformation mechanism is sensitive to the presence of even small nonhydrostatic stresses, however, so there is no reason to infer a disagreement between experiment and theory on this point.
33. Experimentally, we find evidence for a topotactic relation between the two phases, which suggests a martensitic or "military" type transformation [J. W. Christian, The Theory of Transformations in Metals and Alloys, Part I (Pergamon, New York, ed. 2, 1975)]. The (111) peak of the fcc phase and the (002) peak of the hcp phase appear at the same d spacing, which implies identical orientations for the close-packed planes in the two structures [A. F. Schuch, R. L. Mills, D. A. Depatie, Phys. Rev. 165, 1032 (1968)]. A similar geometrical relation explains why three other hcp peaks, (004), (112), and (110), are also coincident with the (222), (311), and (220) fcc peaks. It is possible that the detailed transformation mechanism is sensitive to the presence of even small nonhydrostatic stresses, however, so there is no reason to infer a disagreement between experiment and theory on this point.
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38. Supported by NASA, NSF, and the U.S. Department of Energy (DOE), including grants NSF DMR-9520554 and DOE DE-AC03-76SF00098. The computations were performed on the National Energy Research Scientific Computing Center T3E at Lawrence Berkeley National Laboratory. We thank M. S. T. Bukowinski, R. J. Hemley, M. L. Klein, and R. O. Pepin for helpful discussions.