Lattice phonon modes of the high-pressure phase CuCl-IV

Raman spectra of isotopically pure CuCl samples ((CuCl)-Cu-63 and (CuCl)-Cu -65) were measured under hydrostatic pressure up to 14 GPa at low temperatu re (5 K). Up to six Raman modes were resolved for the binary BC8-analog pha se CuCl-IV in the range from 4.1 to 14 GPa. The phonon dispersion relations of this phase were calculated within a rigid ion model. Based on this calc ulation an assignment for the observed Raman-active modes is proposed. The calculated pressure dependences of mode frequencies reproduce the experimen tal results. Raman spectra support the existence of the phase CuCl-IIa in a narrow pressure range from 3.3 to 4.1 GPa.