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Title: High pressure behaviour of uranium dicarbide (UC{sub 2}): Ab-initio study

Abstract

The structural stability of uranium dicarbide has been examined under hydrostatic compression employing evolutionary structure search algorithm implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with ab-initio electronic band structure calculation method. The ab-initio total energy calculations involved for this purpose have been carried out within both generalized gradient approximations (GGA) and GGA + U approximations. Our calculations under GGA approximation predict the high pressure structural sequence of tetragonal → monoclinic → orthorhombic for this material with transition pressures of ∼8 GPa and 42 GPa, respectively. The same transition sequence is predicted by calculations within GGA + U also with transition pressures placed at ∼24 GPa and ∼50 GPa, respectively. Further, on the basis of comparison of zero pressure equilibrium volume and equation of state with available experimental data, we find that GGA + U approximation with U = 2.5 eV describes this material better than the simple GGA approximation. The theoretically predicted high pressure structural phase transitions are in disagreement with the only high experimental study by Dancausse et al. [J. Alloys. Compd. 191, 309 (1993)] on this compound which reports a tetragonal to hexagonal phase transition at a pressure of ∼17.6 GPa. Interestingly, during lowest enthalpy structure search using USPEX, we do not see any hexagonalmore » phase to be closer to the predicted monoclinic phase even within 0.2 eV/f. unit. More experiments with varying carbon contents in UC{sub 2} sample are required to resolve this discrepancy. The existence of these high pressure phases predicted by static lattice calculations has been further substantiated by analyzing the elastic and lattice dynamic stability of these structures in the pressure regimes of their structural stability. Additionally, various thermo-physical quantities such as equilibrium volume, bulk modulus, Debye temperature, thermal expansion coefficient, Gruneisen parameter, and heat capacity at ambient conditions have been determined from these calculations and compared with the available experimental data.« less

Authors:
; ; ;  [1]
  1. Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
Publication Date:
OSTI Identifier:
22598891
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALGORITHMS; ALLOYS; APPROXIMATIONS; CARBON; COMPARATIVE EVALUATIONS; DEBYE TEMPERATURE; ENTHALPY; EQUATIONS OF STATE; MONOCLINIC LATTICES; ORTHORHOMBIC LATTICES; PHASE TRANSFORMATIONS; PRESSURE RANGE GIGA PA; PRESSURE RANGE MEGA PA 10-100; SPECIFIC HEAT; STABILITY; THERMAL EXPANSION; URANIUM; URANIUM CARBIDES

Citation Formats

Sahoo, B. D., E-mail: bdsahoo@barc.gov.in, Mukherjee, D., Joshi, K. D., and Kaushik, T. C. High pressure behaviour of uranium dicarbide (UC{sub 2}): Ab-initio study. United States: N. p., 2016. Web. doi:10.1063/1.4961497.
Sahoo, B. D., E-mail: bdsahoo@barc.gov.in, Mukherjee, D., Joshi, K. D., & Kaushik, T. C. High pressure behaviour of uranium dicarbide (UC{sub 2}): Ab-initio study. United States. doi:10.1063/1.4961497.
Sahoo, B. D., E-mail: bdsahoo@barc.gov.in, Mukherjee, D., Joshi, K. D., and Kaushik, T. C. Sun . "High pressure behaviour of uranium dicarbide (UC{sub 2}): Ab-initio study". United States. doi:10.1063/1.4961497.
@article{osti_22598891,
title = {High pressure behaviour of uranium dicarbide (UC{sub 2}): Ab-initio study},
author = {Sahoo, B. D., E-mail: bdsahoo@barc.gov.in and Mukherjee, D. and Joshi, K. D. and Kaushik, T. C.},
abstractNote = {The structural stability of uranium dicarbide has been examined under hydrostatic compression employing evolutionary structure search algorithm implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with ab-initio electronic band structure calculation method. The ab-initio total energy calculations involved for this purpose have been carried out within both generalized gradient approximations (GGA) and GGA + U approximations. Our calculations under GGA approximation predict the high pressure structural sequence of tetragonal → monoclinic → orthorhombic for this material with transition pressures of ∼8 GPa and 42 GPa, respectively. The same transition sequence is predicted by calculations within GGA + U also with transition pressures placed at ∼24 GPa and ∼50 GPa, respectively. Further, on the basis of comparison of zero pressure equilibrium volume and equation of state with available experimental data, we find that GGA + U approximation with U = 2.5 eV describes this material better than the simple GGA approximation. The theoretically predicted high pressure structural phase transitions are in disagreement with the only high experimental study by Dancausse et al. [J. Alloys. Compd. 191, 309 (1993)] on this compound which reports a tetragonal to hexagonal phase transition at a pressure of ∼17.6 GPa. Interestingly, during lowest enthalpy structure search using USPEX, we do not see any hexagonal phase to be closer to the predicted monoclinic phase even within 0.2 eV/f. unit. More experiments with varying carbon contents in UC{sub 2} sample are required to resolve this discrepancy. The existence of these high pressure phases predicted by static lattice calculations has been further substantiated by analyzing the elastic and lattice dynamic stability of these structures in the pressure regimes of their structural stability. Additionally, various thermo-physical quantities such as equilibrium volume, bulk modulus, Debye temperature, thermal expansion coefficient, Gruneisen parameter, and heat capacity at ambient conditions have been determined from these calculations and compared with the available experimental data.},
doi = {10.1063/1.4961497},
journal = {Journal of Applied Physics},
number = 8,
volume = 120,
place = {United States},
year = {Sun Aug 28 00:00:00 EDT 2016},
month = {Sun Aug 28 00:00:00 EDT 2016}
}