POSITRON-ANNIHILATION IN SOLID, LIQUID AND UNDERCOOLED MELTS OF CO80PD20

Positron annihilation measurements have been performed in solid, liqui d and undercooled Co80Pd20 alloy using electromagnetic levitation as c ontainerless processing method. The formation enthalpy for a single va cancy is H-1v = (1.7 +/- 0.1) eV. In the melt, the thermal expansion c ontinues linear in the undercooled phase and is larger than that of th e solid alloy. The mean free volume in the liquid phase is slightly la rger than the volume of a single vacancy. At the Curie temperatures of both solid and liquid phase, the S-parameter indicates no effect on t he atomic structure. Different H-2 concentrations in the processing ga s atmosphere have no detectable influence on the data.