Phase transformation in lutetium metal at 88 GPa

The heaviest member of the rare-earth-metal series lutetium has been studied up to a pressure of 163 GPa in a diamond-anvil cell using energy-dispersive x-ray diffraction with a synchtotron source. The pressures were carefully calibrated using copper as an internal x-ray standard. A phase transformation at 88+/-5 GPa is reported from a double-hexagonal-close-packed structure to a distorted fee structure (hR24) with a volume change of 4.9%. Such a first-order transformation is unusual in an element with a filled f shell and may indicate increased hybridization between the localized f shell and the spd conduction band at megabar pressures. We present the equation of state data to 163 GPa and attribute high compressibility to an electronic transfer from s-->d band under pressure. [S0163-1829(98)04118-6].