111Cd-TDPAC study of pressure effect on the valence of Yb in the YbGe2.85 cubic phase

New cubic phases of YbGe2.85, TbGe2.85 and DyGe2.85 crystallized in the AuCu3 structure are synthesized at a pressure of 8 GPa. Using the differential perturbed angular γγ-correlation method (TDPAC) we measure the electric field gradient Vzz   (the quadrupole frequency νQ=eQVZZ/hνQ=eQVZZ/h) at 111Cd nuclei probes inserted in Ge vacancy lattice sites for all these compounds. In YbGe2.85 the electric field gradient (EFG) is obtained as a function of pressure (up to 8 GPa) at room temperature and as a function of temperature (down to 4 K) at normal pressure. In TbGe2.85 and DyGe2.85 EFG is measured only as a function of temperature (down to 77 K) at normal pressure. In YbGe2.85 the change of EFG and νQ with pressure indicate a change of Yb valance from 2.46 at normal pressure to 2.89 at 8 GPa. In all compounds EFG and νQ are found to be practically independent of temperature.

► Cubic phases of YbGe2.85, TbGe2.85 and DyGe2.85 have been synthesized at 8 GPa.
► TDPAC spectra of 111Cd probe nuclei in YbGe2.85, TbGe2.85 and DyGe2.85 were obtained.
► Close similarity between RGe2.85 and RSn3 (R = Yb, Tb, Dy) has been found.
► The dependence of Yb valence in YbGe2.85 on pressure up to 8 GPa has been found.