High-pressure Raman studies of both hcp phases of Ba.*

Both hcp high-pressure phases of Ba were sudied by Raman spectroscopy. Combining the Raman data with existing equation of state data, the pressure dependence of the elastic shear modulus $C_{44} $ has been derived. The pressure shift of the E$_{2g}$ phonon frequency is discussed in terms of elastic parameters. Though the pressure response of the observed phonon mode shows normal behaviour in both phases, more subtle differences can be traced back to differences in the interatomic interactions in both phases.