Study of Bcc-Hcp Iron Phase Transition by Synchrotron Radiation

  1. Murli H. Manghnani and
  2. Yasuhiko Syono
  1. E. Huang,
  2. W. A. Bassett and
  3. P. Tao

Published Online: 21 MAR 2013

DOI: 10.1029/GM039p0165

High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto

High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto

How to Cite

Huang, E., Bassett, W. A. and Tao, P. (2013) Study of Bcc-Hcp Iron Phase Transition by Synchrotron Radiation, in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds M. H. Manghnani and Y. Syono), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM039p0165

Author Information

  1. Department of Geological Sciences, Cornell University Ithaca, New York, 14853, USA

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1987

ISBN Information

Print ISBN: 9780875900667

Online ISBN: 9781118664124

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Keywords:

  • Mineralogy and Crystal Chemistry;
  • Phase transformations;
  • High Pressure-High Temperature Research

Summary

Experiments on the bcc-hcp phase transition in iron were carried out in a high-temperature, high-pressure diamond-anvil cell using synchrotron radiation. Four isothermal runs at room temperature, 150°C, 300°C, and 450°C were accomplished using gold as a pressure calibrant. The onset of the phase transition with increasing pressure was observed to fall in the pressure range of 11.0–11.7 (±0.5) GPa and over the temperature range of 25–450°C. Hence an essentially vertical phase boundary for the onset of transition (hcp-in) was obtained. A two-phase zone was found to exist over a wide pressure range in each isothermal run. Beyond the transition pressure, the extent of the phase transition (measured by the ratio of the two phases) increased with further application of the load. The extent to which bcc iron converted to its high pressure phase was not found to change significantly with time at 18.0 GPa and room temperature. This observation, therefore, is consistent with a stress-dependent martensitic transformation. At 25°C, 150°C, and 300°C, the first appearance of the hcp phase occurred at lower pressure than the reappearance of the bcc phase (bcc-in) with decreasing pressure. The Clapeyron boundary of the bcc-hcp phase transition is determined by averaging the hcp-in and bcc-in pressures at various temperatures. Accordingly, the initial appearance of the hep phase occurs at pressures below the Clapeyron boundary, and the initial appearance of the bcc phase with decreasing pressure occurs at pressures above the Clapeyron boundary, suggesting that the phase transition is strongly controlled by the deviatoric stress. The Clapeyron boundary has a slope (dT/dP) of −283°C/GPa with a transition pressure of 13.5 (±1.0) GPa at room temperature.