High pressure lutetium

Lanthanide bromides and iodides have found important applications in a completely different field. They are added as additives in high-pressure discharge lamps in the lighting industry to improve the arc stability and the colour quality. The latter is due to the contribution of the multiline spectrum of the doped rare earths which are added to the salt mixture. Lanthanide trihalides of dysprosium, holmium, thullium, gadolinium and lutetium are used frequently for this purpose (Hilpert and Niemann, 1997). 

Thulium (Tm) is a unique heavy lanthanide element. It is the last heavy lanthanide with an incomplete 4f shell. In the lanthanide series, thuhum is followed by ytterbium, which has a divalent electronic character and does not show the typical structural changes observed in other trivalent lanthanide elements. And the last element in the lanthanide series lutetium also has a completely filled 4f shell, and therefore is not expected to exhibit low symmetry structures at ultra high pressures. 

Kaminska A, Kaczor P, Durygin A, Suchocki A, Grinberg M (2002) Low-temperature high-pressure spectroscopy of lanthanum lutetium gallium garnet crystals doped with Cr3 -I- and Nd3+. Phys Rev B 65 104106... 

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... 

By high pressure (77 kbars) high temperature (2000°C) treatment, Eatough et al. obtained the Th3P4-type for all the elements up to lutetium, in the R2S3 sulfide series (1969) and in the R2Se3 selenides series (1969, 1970). 

The high-temperature polymorphic form for most of the rare earth metals just before melting is the bcc structure. Four of the trivalent lanthanides (holmium, erbium, thulium and lutetium) are monomorphic and do not form a bcc structure before melting at atmospheric pressure (see fig. 4). However, the bcc phase can be formed in holmium and erbium by the application of pressure (< 1 GPa), see section 3.7.1. The existence of the bcc phase in the lanthanides has been correlated with the d occupation number, which decreases along the lanthanide series, but increases... 

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