Strength and Debye temperature measurements of cerium across the γ → α volume collapse: the lattice contribution.

ABSTRACT

The longitudinal and transverse sound speeds, cL and cT, of polycrystalline cerium were measured under pressure across the iso-structural γ-α phase transition at 0.75 GPa to beyond 3 GPa. In contrast to previous methods all quantities were directly obtained and no assumptions were made about the size of the volume collapse. Up to the transition our values for cL are in excellent agreement with previous ones, while our values for cT are significantly lower. We deduce values for the adiabatic bulk modulus BS, the shear modulus [Formula see text], and the pressure dependent Debye temperature, ΘD(p). ΘD(p) is in good agreement with recent results derived from phonon dispersion measurements on single crystals. The ratio of the Debye temperature values bracketing the transition indicates a lattice contribution to the entropy change across the volume collapse, ΔSvib(γ â†’ α) ≈ (0.68 ± 0.06)kB, consistent with previous results obtained by neutron scattering, but significantly larger than other previously determined values.