Vibrational and elastic properties of hcp barium under pressure and their relation to its electronic structure

High-pressure Raman studies of both hexagonal-close-packed phases Ba-II and Ba-V are reported. Combining the E 2 g phonon data with the existing equation of state data, the pressure dependence of the elastic shear modulus C 44 has been derived. The pressure shift of the E 2 g mode in both phases is discussed in terms of the elastic parameters. Though the pressure response of the observed Raman mode shows normal behaviour in both phases, more subtle differences can be traced back to differences of the electronic structure in both phases.