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High-Pressure Polymorph of Iron

Taro Takahashi and William A. Bassett
Science
New Series, Vol. 145, No. 3631 (Jul. 31, 1964), pp. 483-486
Stable URL: http://www.jstor.org/stable/1714581
Page Count: 4
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High-Pressure Polymorph of Iron
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Abstract

An x-ray diffraction study of iron under pressure has shown that alpha-iron (body-centered cubic) transforms to hexagonal-close-packing (designated epsilon-iron) at 130 kb, room temperature. The volume change for the transformation is - 0.20 ± 0.03 cm$^{3}$/mole. The slope for the gamma-epsilon phase boundary has been calculated to be 2 ± 1°C/kb. The molar volume of iron decreases from 7.10 cm$^{3}$/mole (density = 7.85 g/cm$^{3}$) at room pressure to 6.10 ± 0.08 cm$^{3}$/mole (density = 9.1 ± 0.1 g/cm$^{3}$) at 200 kb and room temperature. The extrapolation of the gamma-epsilon phase boundary, consistent with shock wave data, suggests that it may have an influence on the properties of the earth's core.

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