Phonon anharmonicity and components of the entropy in palladium and platinum

Abstract

Inelastic neutron scattering was used to measure the phonon density of states in fcc palladium and platinum metal at temperatures from 7 K to 1576 K. Both phonon-phonon interactions and electronphonon interactions were calculated by methods based on density functional theory (DFT), and were consistent with the measured shifts and broadenings of phonons with temperature. Unlike the longitudinal modes, the characteristic transverse modes had a nonlinear dependence on temperature owing to the requirement for a population of thermal phonons for upscattering. Kohn anomalies were observed in the measurements at low temperature, and were reproduced by calculations based on DFT. Contributions to the entropy from phonons and electrons were assessed and summed to obtain excellent agreement with prior calorimetric data. The entropy from thermal expansion is positive for both phonons and electrons, but larger for phonons. The anharmonic phonon entropy is negative in Pt, but in Pd it changes from positive to negative with increasing temperature. Owing to the position of the Fermi level on the electronic DOS, the electronic entropy was sensitive to the adiabatic electron-phonon interaction in both Pd and Pt. The adiabatic EPI depended strongly on thermal atom displacements.

Temperature dependence of phonons in Pd3Fe through the Curie temperature

“…We suggest that the palladium atoms dominate the anharmonic phonon-phonon interactions in L1 2 -ordered Pd 3 Fe. This is consistent with how fcc Pd shows strong PPI at high temperatures [63].…”

Effect of air confinement on thermal contact resistance in nanoscale heat transfer

“…We assume that materials Pt, Ti and SiO2 are homogeneous and isotropic. The data of Pt, Ti and SiO2 are taken from the literature [31][32][33] and the values of all required parameter used in the models are listed in Table I. Using the average sound velocities in the materials, the values of  and G are determined which is listed in Table II.…”

Design and operating characteristic of a vacuum furnace for time-of-flight inelastic neutron scattering measurements

“…This furnace has been used in the study of metallic glasses, 2 silicon, 3 yttrium-stabilized zirconia, 5 Ag 2 O, 7 and Pt. 13 The active heating elements are interchangeable and are constructed of either two nested niobium or vanadium foil cylinders with low intrinsic resistance. The inner cylinder of the element has an internal diameter of 80 mm with a foil thickness of 0.05 mm.…”

“…Active research areas in condensed matter physics and materials science at elevated temperatures include studies of phonon anharmonicity in functional materials, [1][2][3][4][5][6][7][8] localization dynamics, [9][10][11] phonon entropy, 12,13 and local dynamics of metallic liquids. 14 The neutron is a weakly interacting probe of matter, allowing researchers to perform neutron scattering measurements on condensed matter systems with samples placed within complicated environments such as cryostats, furnaces, magnets, and pressure cells.…”