Ab initio study of phase transition and bulk modulus of NaH
- National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900 (China)
- Institute of Atomic and Molecular Physics, School of Physical Science and Technology, Sichuan University, Chengdu 610065 (China)
The phase transition of NaH from NaCl- to CsCl-type structure is investigated by an ab initio plane-wave pseudopotential density functional theory method with the norm-conserving pseudopotential scheme in the frame of the generalized gradient approximation correction; the isothermal bulk modulus and its first and second pressure derivatives of the NaCl- and CsCl-type structures under high pressure and temperature are obtained through the quasi-harmonic Debye model. The phase transition obtained from the usual condition of equal enthalpies occurs at the pressure of 32 GPa, which is consistent with the experimental and other calculated values. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of cell volume V and lattice constant a on temperature T at zero pressure, the isothermal bulk modulus B{sub 0} and its pressure derivatives B{sub 0}'and B{sub 0}'' on pressure P along isotherms 0, 300, and 600 K, are also successfully obtained. -- The isothermal bulk modulus B{sub T}, adiabatic bulk modulus B{sub S}, primitive cell volume V, and lattice constant a of an NaH with an NaCl-type structure as a function temperature T at zero pressure. When T<100 K, B nearly keeps constant; when T>100 K, B decreases dramatically as T increases. Correspondingly, when T<100 K, the primitive cell volume and lattice parameter of an NaH with an NaCl-type structure have a little change; when T>100 K, the primitive cell volume and lattice parameter changes rapidly as T increases. It is the rapid volume or lattice parameter variation that makes the bulk modulus B rapidly decrease. Display Omitted Research highlights: The transition phase of an NaH from NaCl to CsCl structure has been investigated. The relationship between B and T for an NaH at zero pressure has been given. The B{sub T} and its pressure derivatives of an NaH at high pressure have been obtained.
- OSTI ID:
- 21496546
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 184; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ALKALI METAL COMPOUNDS
CALCULATION METHODS
CHLORIDES
CHLORINE COMPOUNDS
DENSITY FUNCTIONAL METHOD
ENTHALPY
HALIDES
HALOGEN COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
LATTICE PARAMETERS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PRESSURE RANGE
PRESSURE RANGE GIGA PA
SODIUM CHLORIDES
SODIUM COMPOUNDS
SODIUM HYDRIDES
TEMPERATURE RANGE
TEMPERATURE RANGE 0000-0013 K
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
THERMODYNAMIC PROPERTIES
VARIATIONAL METHODS