High-Pressure Polymorph of Iron

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Science  31 Jul 1964:
Vol. 145, Issue 3631, pp. 483-486
DOI: 10.1126/science.145.3631.483


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 cm2/ 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 cm3/mole (density = 7.85 g/cm3) at room pressure to 6.10 ± 0.08 cm3/mole (density = 9.1 ± 0.1 g/cm3) 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