Europium under high pressure

Fee ytterbium at atmospheric pressure and room temperature is a metal. With the application of pressure Yb becomes a semi-metal and then a semiconductor. The semiconducting fee phase transforms into a metallic bcc phase at about 40 kbar (Jayaraman 1978), while Divakar et al. (1984) give 33 kbar. The relative volume change is about 3%. Another structural phase transformation (bcc-hcp) occurs at 260-309 kbar (cf. Takemura and Syassen 1985). Similar to europium the p-V isotherm of the adjacent trivalent reference element lutetium is found to intersect that of Yb at about 200 kbar (at 300 K). Syassen et al. (1981,1982) measured the L, absorption in Yb under high pressure up to 340 kbar with a conventional laboratory spectrometer. Divalent Yb clearly transforms into a mixed valent state at 40 kbar... 

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