Martensitic fcc-to-hcp transformation observed in xenon at high pressure

Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that th e fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diam ond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fee l attice at low pressure, which grows into hcp domains with increasing pressu re. The small energy difference between the hcp and the fee structures may allow the two phases to coexist over a wide pressure range. Evidence of sim ilar stacking disorder and incipient growth of an hcp phase are also observ ed in solid Kr.