SPECIFIC-HEAT OF D-HCP AND FCC LANTHANUM UNDER HIGH-PRESSURE

Specific heat measurements have been performed under pressures up to 2.5 GPa on single phase d-hcp lanthanum and a mixed phase sample yielding also results on fcc La. An evaluation of the pressure dependences of the Debye temperature KELVIN(D) and the electronic specific heat coefficient gamma has been possible and shows distinct differences between the two phases. While for the d-hcp phase marked variations with pressure have been found, there is hardly no change seen in fcc La. In d-hcp La the most remarkable results are an initial increase of gamma, which cannot be explained by the increase of the electron-phonon coupling parameter lambda alone and, therefore, indicates an increase of the band structure density of states, as well as a strong softening of THETA(D) at higher pressures. These results are discussed in the context of the existing knowledge on lanthanum.