Anharmonic effective pair potentials of group VIII and Ib fcc metals

The temperature dependence of EXAFS Debye-Waller factors and anharmonic effective pair potentials of group VIII and Ib fcc metals were investigated by a cumulant expansion method. The EXAFS spectra near K- or L₃-edges were measured at the temperatures from 30 to 800 K using synchrotron radiation from the Photon Factory, Tsukuba. The effective pair potentials, a·u²/2!+ b·u³/3! denote that the group Ib has obviously larger anharmonisity than the group VIII metals. The discrepancy between the Morse potential approximation and determined effective pair potential is discussed.