Vibrational Properties of α - and σ -Phase Fe-Cr Alloy

Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, aleja Mickiewicza 30, 30-059 Krakow, Poland.
Physical Review Letters (Impact Factor: 7.51). 04/2010; 104(15):155503. DOI: 10.1103/PhysRevLett.104.155503
Source: PubMed

ABSTRACT Experimental and theoretical studies, of the Fe-partial phonon density of states (PDOS) for Fe52.5Cr47.5 alloy having alpha and sigma phases were carried out. The former using the nuclear resonant inelastic x-ray scattering method, and the latter with the direct one. Characteristic features of PDOS, which distinguish one phase from the other, were revealed and successfully reproduced by the theory. Data pertinent to the dynamics such as the Lamb-Mössbauer factor, f, the kinetic energy per atom, E(k), and the mean force constant, D, were directly derived, while vibrational specific heat at constant volume, C(V), and vibrational entropy, S were calculated using the Fe partial PDOS. Based on the values of f and C(V), we determined Debye temperatures, Theta(D). An excellent agreement for some quantities derived from experiment and first-principles theory, like C(V) and quite good ones for others like D and S were obtained.

Download full-text


Available from: Wolfgang Sturhahn, Sep 29, 2015
33 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: There has been increasing evidence about the effects of short-range order (or local chemical environment effects) on the lattice dynamics of alloys, which eventually affect the vibrational entropy difference among various phases of a compound, and hence their relative stability. In this article, we present an ab initio calculation of the lattice dynamics and the vibrational entropy of disordered systems with short-range order. The features in the phonon density of states were found to change systematically with chemical short-range order in the alloy. Plausible explanations for our smaller value of vibrational entropy of mixing compared to experiment are given in some detail. A general trend of the magnitude of vibrational entropy of mixing is explained by making a connection to the phonon lifetime broadening, an intrinsic property of any multiple scattering phenomenon. We illustrate the method by applying it to a body-centered cubic Fe1-xCrx alloy.
    Physical review. B, Condensed matter 02/2011; 83(5). DOI:10.1103/PhysRevB.83.054201 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Formation energy of the $\sigma$-phase in the Fe-Cr alloy system, $\Delta E$, was computed versus the occupancy changes on each of the five possible lattice sites. Its dependence on a number of Fe-atoms per unit cell, $N_{Fe}$, was either monotonically increasing or decreasing function of $N_{Fe}$, depending on the site on which Fe-occupancy was changed. Based on the calculated $\Delta E$ - values, the average formation energy, $<\Delta E>$, was determined as a weighted over probabilities of different atomic configurations. The latter has a minimum in the concentration range where the $\sigma$-phase exists. The minimum in that range of composition was also found for the free energy calculated for 2000 K and taking only the configurational entropy into account.
    Intermetallics 03/2011; 24. DOI:10.1016/j.intermet.2012.01.023 · 2.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A review is presented on physical properties of the sigma-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental -- mostly with the Mossbauer spectroscopy -- and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of sigma and determination of its structural properties, kinetics of alpha-to-sigma and sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.
    Critical Reviews in Solid State and Material Sciences 05/2011; 36(4). DOI:10.1080/10408436.2011.589232 · 6.45 Impact Factor
Show more