Effect of pressure on the valence state of Yb in YbPd2Si2

The intermediate valent behaviour of YbPd₂Si₂ has been studied under pressure in the temperature range from 1.2 K to 90 K by using the 84 keV Mössbauer transition in¹⁷⁰Yb. At 54 kbar and 4.2 K we obtain an increase of the electric field gradient (EFG) by a factor of 3. In addition, the EFG varies strongly with temperature, in contrast to the behaviour at ambient pressure. At 1.2 K a change of the hyperfine pattern is observed indicating a magnetic character of the Yb ion. These results provide evidence of a pressure induced change of the valence state close to 3+.Work supported by the Deutsche Forschungsgemeinschaft