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Title: Hidden disorder in the [alpha];#8242;;#8594;[sigma] transformation of Pu-1.9 at. % Ga

Abstract

Enthalpy and entropy are thermodynamic quantities critical to determining how and at what temperature a phase transition occurs. At a phase transition, the enthalpy and temperature-weighted entropy differences between two phases are equal ({Delta}H=T{Delta}S), but there are materials where this balance has not been experimentally or theoretically realized, leading to the idea of hidden order and disorder. In a Pu-1.9 at. % Ga alloy, the {delta} phase is retained as a metastable state at room temperature, but at low temperatures, the {delta} phase yields to a mixed-phase microstructure of {delta}- and {alpha}{prime}-Pu. The previously measured sources of entropy associated with the {alpha}{prime} {yields} {delta} transformation fail to sum to the entropy predicted theoretically. We report an experimental measurement of the entropy of the {alpha}{prime} {yields} {delta} transformation that corroborates the theoretical prediction, and implies that only about 65% of the entropy stabilizing the {delta} phase is accounted for, leaving a missing entropy of about 0.5 k{sub B}/atom. Some previously proposed mechanisms for generating entropy are discussed, but none seem capable of providing the necessary disorder to stabilize the {delta} phase. This hidden disorder represents multiple accessible states per atom within the {delta} phase of Pu that may not be includedmore » in our current understanding of the properties and phase stability of {delta}-Pu.« less

Authors:
; ; ; ;  [1]
  1. (LLNL)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
DOE-NNSA
OSTI Identifier:
1046864
Resource Type:
Journal Article
Journal Name:
Phys. Rev. B
Additional Journal Information:
Journal Volume: 85; Journal Issue: (22) ; 06, 2012
Country of Publication:
United States
Language:
ENGLISH
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; ENTHALPY; ENTROPY; FORECASTING; METASTABLE STATES; MICROSTRUCTURE; PHASE STABILITY; THERMODYNAMICS; TRANSFORMATIONS

Citation Formats

Jeffries, J.R., Manley, M.E., Wall, M.A., Blobaum, K.J.M., and Schwartz, A.J. Hidden disorder in the [alpha];#8242;;#8594;[sigma] transformation of Pu-1.9 at. % Ga. United States: N. p., 2012. Web. doi:10.1103/PhysRevB.85.224104.
Jeffries, J.R., Manley, M.E., Wall, M.A., Blobaum, K.J.M., & Schwartz, A.J. Hidden disorder in the [alpha];#8242;;#8594;[sigma] transformation of Pu-1.9 at. % Ga. United States. doi:10.1103/PhysRevB.85.224104.
Jeffries, J.R., Manley, M.E., Wall, M.A., Blobaum, K.J.M., and Schwartz, A.J. Wed . "Hidden disorder in the [alpha];#8242;;#8594;[sigma] transformation of Pu-1.9 at. % Ga". United States. doi:10.1103/PhysRevB.85.224104.
@article{osti_1046864,
title = {Hidden disorder in the [alpha];#8242;;#8594;[sigma] transformation of Pu-1.9 at. % Ga},
author = {Jeffries, J.R. and Manley, M.E. and Wall, M.A. and Blobaum, K.J.M. and Schwartz, A.J.},
abstractNote = {Enthalpy and entropy are thermodynamic quantities critical to determining how and at what temperature a phase transition occurs. At a phase transition, the enthalpy and temperature-weighted entropy differences between two phases are equal ({Delta}H=T{Delta}S), but there are materials where this balance has not been experimentally or theoretically realized, leading to the idea of hidden order and disorder. In a Pu-1.9 at. % Ga alloy, the {delta} phase is retained as a metastable state at room temperature, but at low temperatures, the {delta} phase yields to a mixed-phase microstructure of {delta}- and {alpha}{prime}-Pu. The previously measured sources of entropy associated with the {alpha}{prime} {yields} {delta} transformation fail to sum to the entropy predicted theoretically. We report an experimental measurement of the entropy of the {alpha}{prime} {yields} {delta} transformation that corroborates the theoretical prediction, and implies that only about 65% of the entropy stabilizing the {delta} phase is accounted for, leaving a missing entropy of about 0.5 k{sub B}/atom. Some previously proposed mechanisms for generating entropy are discussed, but none seem capable of providing the necessary disorder to stabilize the {delta} phase. This hidden disorder represents multiple accessible states per atom within the {delta} phase of Pu that may not be included in our current understanding of the properties and phase stability of {delta}-Pu.},
doi = {10.1103/PhysRevB.85.224104},
journal = {Phys. Rev. B},
number = (22) ; 06, 2012,
volume = 85,
place = {United States},
year = {2012},
month = {10}
}