Crystal Dynamics of Platinum by Inelastic Neutron Scattering

Abstract

The dispersion relations in platinum have been measured at 90 °K by the inelastic scattering of thermal neutrons. Born–von Kármán models of the force system have been calculated by fitting to the dispersion curves. Fourth-neighbor forces, with weaker interactions probably extending to at least sixth neighbors, are required to fit the data. A frequency distribution has been calculated from the force constants of the most realistic model.Some measurements are also reported of frequencies at a temperature of 473 °K. The mean frequency shift from 90 to 473 °K was found to be −2.0%.In the [0ζζ]T1 branch, anomalous behavior, similar to that observed in palladium, has been studied at temperatures of 90, 296, and 473 °K. As in Pd, the anomaly in Pt is markedly broadened and weakened with increasing temperature. The phonon wave vectors corresponding to possible Kohn transitions in the (001) plane have been determined by machine calculation, using Fermi surfaces given in the literature. These results strongly suggest that the anomaly along the T1 branch arises largely from transitions across the "heavy" hole Fermi sheet formed from the fifth-band electrons. A comparison is made with similar results for palladium and nickel.