High pressure behaviour of uranium dicarbide (UC{sub 2}): Ab-initio study
- Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
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.
- OSTI ID:
- 22598891
- Journal Information:
- Journal of Applied Physics, Vol. 120, Issue 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
Similar Records
Low-temperature Polymorphs of ZrO2 and HfO2. A Density Functional Theory Study
Polymorphism in Strontium Tungstate SrWO4 under Quasi-Hydrostatic Compression
Related Subjects
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