Inelastic X-ray scattering in Cs under pressure

摘要

The pressure dependences of the longitudinal acoustic (LA), Q=(100) phonon frequencies in the bcc and fcc phases of Cs at pressures up to 4 GPa were studied by synchrotron inelastic X-ray scattering. We observed a markedly sublinear pressure dependence of the LA-(100) phonon frequency in the bcc phase near the bcc-fcc transition at 2.2 GPa. In the fcc phase, the LA-(100) phonon energy is essentially pressure independent within the experimental uncertainty. The experiments are complemented by first-principles calculations. They affirm the anomaly in bcc-Cs near the bcc-fcc transition. In fcc-Cs, they indicate a very small variation of the LA-(100) phonon frequency with a maximum near the center of the fcc stability range.