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Lattice vibrations and electronic transitions in the rare-earth metals: yttrium, gadolinium and lutetium

Lattice vibrations in high-pressure phases of Y, Gd and Lu were studied by Raman spectroscopy. The observed phonon frequencies decrease towards the transitions to the dhcp and fcc phases. There is evidence that the entire structural sequence under pressure for the individual regular rare-earth metals and along the lanthanide series at ambient pressure involve softening of certain acoustic and optical phonon modes and of the elastic shear modulus C44. Comparison is made to transitions between close-packed lattices in other metals, and possible correlations to s–d electron transfer are discussed.