Absorption spectrophotometric studies of some lanthanide and actinide halides under pressure

Abstract

Diamond anvil cells have been used for absorption spectrophotometric studies of lanthanide and actinide halides over a pressure range of 10 −4 to > 30 GPa. Irreversible spectral changes with pressure in AmI 3 and CfBr 3 have previously been correlated with structural transformations to a more dense form of both compounds. Reversible spectral changes with pressure are more difficult to interpret. In NdCl 3 the spectral changes as pressure is increased suggest the formation of a phase of higher symmetry. With compression of AmCl 3, the spectral changes observed are more subtle. CfCl 3 retains its hexagonal structure at pressures up to 22 GPa. Other studies of Cf(III) chlorides have indicated the formation of a new compound, as yet unidentified, whose spectra as a function of pressure also exhibit reversible changes. Complementary X-ray diffraction data, presently lacking, would help elucidate these phenomena.