skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Prediction of new high pressure structural sequence in thorium carbide: A first principles study

Abstract

In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability inmore » the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57, 280 (1975)].« less

Authors:
; ;  [1]
  1. Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
Publication Date:
OSTI Identifier:
22410201
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 117; Journal Issue: 18; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CARBON; CESIUM CHLORIDES; COMPARATIVE EVALUATIONS; DEBYE TEMPERATURE; ELECTRONIC STRUCTURE; ENTHALPY; FREE ENERGY; ORTHORHOMBIC LATTICES; PHONONS; PRESSURE DEPENDENCE; PRESSURE RANGE GIGA PA; SODIUM CHLORIDES; SPECIFIC HEAT; SUBSTOICHIOMETRY; THERMAL EXPANSION; THORIUM CARBIDES

Citation Formats

Sahoo, B. D., E-mail: bdsahoo@barc.gov.in, Joshi, K. D., and Gupta, Satish C. Prediction of new high pressure structural sequence in thorium carbide: A first principles study. United States: N. p., 2015. Web. doi:10.1063/1.4920929.
Sahoo, B. D., E-mail: bdsahoo@barc.gov.in, Joshi, K. D., & Gupta, Satish C. Prediction of new high pressure structural sequence in thorium carbide: A first principles study. United States. doi:10.1063/1.4920929.
Sahoo, B. D., E-mail: bdsahoo@barc.gov.in, Joshi, K. D., and Gupta, Satish C. Thu . "Prediction of new high pressure structural sequence in thorium carbide: A first principles study". United States. doi:10.1063/1.4920929.
@article{osti_22410201,
title = {Prediction of new high pressure structural sequence in thorium carbide: A first principles study},
author = {Sahoo, B. D., E-mail: bdsahoo@barc.gov.in and Joshi, K. D. and Gupta, Satish C.},
abstractNote = {In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57, 280 (1975)].},
doi = {10.1063/1.4920929},
journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 18,
volume = 117,
place = {United States},
year = {2015},
month = {5}
}