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Title: Lattice dynamics and phase diagram of aluminum at high temperatures

Abstract

The dispersion of phonons in the fcc, hcp, and bcc phases of aluminum is calculated at ultrahigh pressures by the method of small displacements in a supercell. The stability of the phonon subsystem is studied. The thermodynamic characteristics are calculated in the quasi-harmonic approximation, and a phase diagram of aluminum is plotted. As compared to the Debye model, the use of a phonon spectrum calculated in the quasi-harmonic approximation significantly broadens the hcp phase field and strongly shifts the phase boundary between the fcc and bcc phases. The normal isentrope is calculated at megabar pressures. It is shown to intersect the fcc-hcp and hcp-bcc phase boundaries. The sound velocity along the normal isentrope is calculated. It is shown to have a nonmonotonic character.

Authors:
; ; ;  [1]; ;  [2]
  1. National Research Nuclear University 'MEPhI,', Sarov State Institute of Physics and Technology (Russian Federation)
  2. Russian Federal Nuclear Center-All-Russian Research Institute of Experimental Physics (Russian Federation)
Publication Date:
OSTI Identifier:
22210404
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 117; Journal Issue: 4; Other Information: Copyright (c) 2013 Pleiades Publishing, Inc.; http://www.springer-ny.com; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALUMINIUM; APPROXIMATIONS; BCC LATTICES; COMPARATIVE EVALUATIONS; FCC LATTICES; HCP LATTICES; PHASE DIAGRAMS; PHONONS; SPECTRA; TEMPERATURE RANGE 0400-1000 K; THERMODYNAMIC PROPERTIES

Citation Formats

Kudasov, Yu. B., E-mail: yu_kudasov@yahoo.com, Surdin, O. M., Korshunov, A. S., Pavlov, V. N., Frolova, N. V., and Kuzin, R. S.. Lattice dynamics and phase diagram of aluminum at high temperatures. United States: N. p., 2013. Web. doi:10.1134/S1063776113100038.
Kudasov, Yu. B., E-mail: yu_kudasov@yahoo.com, Surdin, O. M., Korshunov, A. S., Pavlov, V. N., Frolova, N. V., & Kuzin, R. S.. Lattice dynamics and phase diagram of aluminum at high temperatures. United States. doi:10.1134/S1063776113100038.
Kudasov, Yu. B., E-mail: yu_kudasov@yahoo.com, Surdin, O. M., Korshunov, A. S., Pavlov, V. N., Frolova, N. V., and Kuzin, R. S.. Tue . "Lattice dynamics and phase diagram of aluminum at high temperatures". United States. doi:10.1134/S1063776113100038.
@article{osti_22210404,
title = {Lattice dynamics and phase diagram of aluminum at high temperatures},
author = {Kudasov, Yu. B., E-mail: yu_kudasov@yahoo.com and Surdin, O. M. and Korshunov, A. S. and Pavlov, V. N. and Frolova, N. V. and Kuzin, R. S.},
abstractNote = {The dispersion of phonons in the fcc, hcp, and bcc phases of aluminum is calculated at ultrahigh pressures by the method of small displacements in a supercell. The stability of the phonon subsystem is studied. The thermodynamic characteristics are calculated in the quasi-harmonic approximation, and a phase diagram of aluminum is plotted. As compared to the Debye model, the use of a phonon spectrum calculated in the quasi-harmonic approximation significantly broadens the hcp phase field and strongly shifts the phase boundary between the fcc and bcc phases. The normal isentrope is calculated at megabar pressures. It is shown to intersect the fcc-hcp and hcp-bcc phase boundaries. The sound velocity along the normal isentrope is calculated. It is shown to have a nonmonotonic character.},
doi = {10.1134/S1063776113100038},
journal = {Journal of Experimental and Theoretical Physics},
number = 4,
volume = 117,
place = {United States},
year = {Tue Oct 15 00:00:00 EDT 2013},
month = {Tue Oct 15 00:00:00 EDT 2013}
}
  • Potassium oxide vaporizes from solutions in SiO/sub 2/ primarily according to the equation: KO/sub 0/./sub 5/(1) ..-->.. K(g) + /sup 1///sub 4/O/sub 2/(g) (1). We have studied this equilibrium using atomic absorption in a constant temperature graphite furnace to measure the absorbance of the steady-state distribution of potassium atoms. The potassium atoms were introduced at the center of the furnace by diffusion through an orifice in sample cells which we developed for vapor pressure measurement. We have shown both experimentally and theoretically that, at a particular temperature, the absorbance we measure is proportional to the rate of diffusion of potassiummore » atoms from the vapor pressure sample cells. For a particular cell with a particular orifice, there is a temperature-dependent conversion factor between absorbance and pressure which we evaluated from measurements with potassium aluminate standards in the cells. The pressure of potassium atoms was measured over a sufficient range of temperature to obtain the heat of vaporization. The Redlich-Kister coefficients for the enthalpy of mixing of liquid KO/sub 0/./sub 5/ and SiO/sub 2/ (A = -86, B = -53 kcal mol/sup -1/) were obtained from this data and estimates for the thermodynamic properties of KO/sub 0/./sub 5/ (liquid), literature data on the enthalpy of glasses, the temperature dependence of rate of vaporization, and the variation of the activity of SiO/sub 2/ with temperature. Redlich-Kister coefficients for log ..gamma../sub KO/sub 0.5// were obtained from the concentration dependence of the vapor pressure of potassium over the KO/sub 0/./sub 5/-SiO/sub 2/ samples: A = -10.9923, B = -6.7801, and C = -1.0101 at 1500 K. From these values, together with the enthalpy coefficients above, activities of both KO/sub 0/./sub 5/ and SiO/sub 2/ can be calculated over a wide range of temperatures and compositions. The KO/sub 0/./sub 5/-SiO/sub 2/ phase diagram was calculated from these values. Thermodynamic quantities are given for tridymite and for two potassium silicates, K/sub 2/Si/sub 4/O/sub 9/ and K/sub 2/Si/sub 2/O/sub 5/.« less
  • The phase diagram of uranium has been studied to 100 GPa by {ital in situ} diamond-anvil cell x-ray/laser-heating experiments. The {gamma} (bcc) phase is discovered at high pressures, and the melting curve is presented to 100 GPa. The {gamma} phase, B=113.3GPa, is approximately 20{percent} softer than the {alpha}(orthorhombic), B=135.5GPa. The volume change in the {alpha}/{gamma} transition shows a strong pressure dependence, ranging from 6{percent} at ambient pressure to less than 1{percent} at 80 GPa. Free-energy calculations, using Debye-Gr{umlt u}neisen quasiharmonic theory, show that the softer bulk modulus of the {gamma} phase, compared to the {alpha} phase, stabilizes the {gamma} phasemore » at high temperatures. {copyright} {ital 1998} {ital The American Physical Society}« less