Vibrational entropy of L12 Cu3Au measured by inelastic neutron scattering
نویسندگان
چکیده
The phonon density of states of elemental Au, Cu, and Cu3Au with L12 chemical order were measured by inelastic neutron scattering and used to calculate the vibrational entropy of formation of the ordered compound from the elemental metals. A vibrational entropy of formation of (0.0660.03) kB /atom at 300 K was obtained, with the vibrational entropy of the ordered alloy being larger than that of the elemental metals. The phonon DOS of the disordered Cu3Au was simulated by adding the phonon DOS curves of fcc Cu, L12 Cu3Au, and fcc Au to match the numbers of first-nearest-neighbor pairs in a disordered alloy. The vibrational entropy obtained with this simulated DOS disagrees with calorimetric data and theoretical estimates, indicating that the phonon DOS of disordered Cu3Au depends on chemical order at spatial lengths larger than is set by first-nearestneighbor pairs. @S0163-1829~99!02429-7#
منابع مشابه
Vibrational and electronic entropy of b-cerium and g-cerium measured by inelastic neutron scattering
Time-of-flight ~TOF! inelastic neutron-scattering spectra were measured on b-cerium ~double hcp! and g-cerium ~fcc! near the phase-transition temperature. Phonon densities of states ~DOS! and crystal-field levels were extracted from the TOF spectra. A softening of the phonon DOS occurs in the transition from bto g-cerium, accounting for an increase in vibrational entropy of DSvib 5(0.0960.05)kB...
متن کاملUsing bond-length-dependent transferable force constants to predict vibrational entropies in Au-Cu, Au-Pd, and Cu-Pd alloys
A model is tested to rapidly evaluate the vibrational properties of alloys with site disorder. It is shown that length-dependent transferable force constants exist and can be used to accurately predict the vibrational entropy of substitutionally ordered and disordered structures in Au-Cu, Au-Pd, and Cu-Pd. For each relevant force constant, a length-dependent function is determined and fitted to...
متن کاملVibrational entropy of spinodal decomposition in FeCr
Inelastic neutron-scattering spectra were measured on stoichiometric Fe0.50Cr0.50 prepared as a bodycentered-cubic bcc solid solution, and after increasing amounts of chemical unmixing on the bcc lattice induced by annealing the solid solution at 773 K. These spectra were reduced by a conventional procedure to a neutron-weighted vibrational density of states. Mössbauer spectrometry was used to ...
متن کاملPhonon entropy of alloying and ordering of Cu-Au
Inelastic neutron scattering spectra were measured with a time-of-flight spectrometer on six disordered Cu-Au alloys at 300 K. The neutron-weighted phonon density of states was obtained from a conventional analysis of these spectra. Several methods were developed to account for this neutron weighting and obtain the phonon entropy of the disordered alloys. The phonon entropies of formation of di...
متن کاملAtom clusters and vibrational excitations in chemically - disordered Pt 3 57 Fe
Inelastic nuclear resonant scattering spectra of Fe atoms were measured on crystalline alloys of Pt3 Fe that were chemically disordered, partially ordered, and L12 ordered. Phonon partial density of states curves for Fe were obtained from these spectra. Upon disordering, about 10% of the spectral intensity underwent a distinct shift from 25 to 19 meV. This change in optical modes accounted for ...
متن کامل