Vibrational properties of alpha- and sigma-phase Fe-Cr alloy

TL;DR

This study combines experimental and theoretical approaches to analyze the vibrational properties of alpha- and sigma-phase Fe-Cr alloys, revealing phase-specific phonon density-of-states and related thermodynamic quantities with high accuracy.

Contribution

It provides a comprehensive comparison of experimental and theoretical phonon density-of-states for Fe-Cr alloys, highlighting phase-dependent vibrational features and deriving key thermodynamic parameters.

Findings

Distinct phonon DOS features for alpha- and sigma-phases

Excellent agreement in vibrational specific heat between experiment and theory

Good agreement in mean force constant and vibrational entropy

Abstract

Experimental investigation as well as theoretical calculations, of the Fe-partial phonon density-of-states (DOS) for nominally Fe_52.5Cr_47.5 alloy having (a) alpha- and (b) sigma-phase structure were carried out. The former at sector 3-ID of the Advanced Photon Source, using the method of nuclear resonant inelastic X-ray scattering, and the latter with the direct method [K. Parlinski et al., Phys. Rev. Lett. {78, 4063 (1997)]. The characteristic features of phonon DOS, which differentiate one phase from the other, were revealed and successfully reproduced by the theory. Various data pertinent to the dynamics such as Lamb-Mossbauer factor, f, kinetic energy per atom, E_k, and the mean force constant, D, were directly derived from the experiment and the theoretical calculations, while vibrational specific heat at constant volume, C_V, and vibrational entropy, S were calculated using the Fe-partial DOS. Using the values of f and C_V, we determined values for Debye temperatures, T_D. An excellent agreement for some quantities derived from experiment and first-principles theory, like C_V and quite good one for others like D and S was obtained.