Charge Transfer in Intermetallics: HfPt sub 3.

The charge transfer in HfPt sub 3 is discussed on the basis of the 4f core-electron binding-energy shifts of the constituent elements. Based on binding energies measured relative to the Fermi levels, both Hf and Pt have positive shifts in the compound. According to a Born-Haber cycle analysis these shifts are directly attributable to the large enthalpy of formation of HfPt sub 3. Corrected for the contact potential difference between the element and the compound, the shift of the Hf is somewhat larger, but that of the Pt is negative, indicating a net flow of electronic charge from Hf to Pt. This is in accord with expectations based on the electronegativity difference and with the semi-empirical model of Miedema, et al., but counter to the direction of charge flow in the Engel-Brewer analysis of bonding.