Hysteresis in the high pressure transformation of bcc- to hcp-iron

The α-Fe/ε-Fe phase transformation has been studied by the Mössbauer effect of 57Fe in a diamond anvil cell at hydrostatic pressures up to 24 GPa. The α/ε composition is easily derived as a function of intermediate pressure. For rising pressures the transition onset is about 9 GPa and half of the α-Fe is converted to ε-Fe by 15 GPa; for lowering pressures half of the ε-Fe is converted to α-Fe by 9 GPa. The transition pressures, widths, and hysteresis widths are compared to those obtained by other techniques.