Theoretical study of electron-phonon interaction in [beta]-phase NiTi and Ni-Al alloys
NiTi and Ni-Al alloys are two materials which exhibit martensitic phase transformations. At high temperature, both alloys possess the CSCl-type or B2 structure with a simple cubic (SC) lattice. They are often called [beta]-phase alloys. As temperature is lowered, the [beta]-phase NiTi and Ni-Al alloys undergo premartensitic phase transformations or premartensitic anomalies before the martensitic phase transformation. Neutron scattering measurements have found that the TA[sub 2] [110] phonon modes in the [beta]-phases are temperature dependent and exhibit anomalous behavior which is responsible for the premartensitic anomalies. The electron-phonon interaction and the phonon anomalies in [beta]-phase NiTi and Ni-Al alloys have been studied. The microscopic mechanisms of the phonon anomaly have been examined carefully. The electronic structures of [beta]-phase NiTi and Ni-Al alloys have been calculated by the first-principles LCAO (linear combination of atomic orbitals) method. Then the first-principles band structures were fitted using a non-orthogonal Slater-Koster tight binding (TB) Hamiltonian which is used in the calculation of the electron-phonon (e-ph) interaction. The contribution of the e-ph interaction to the phonon dynamical matrix was calculated by the method of Varma and Weber. Strong electron-proton interactions together with a nesting feature of the Fermi surface was the source of anomalous behavior of the low frequency TA[sub 2] phonon branch along the [rvec q] = [110] direction. Temperature dependences of TA[sub 2] phonons were examined carefully. The thermal smearing effect of the nesting feature of the Fermi surface makes the soft phonon stable. A rigid band model was used to study the concentration dependence of the phonon anomaly in [beta]-phase Ni[sub x]Al[sub 1[minus]x] alloys. The position of the phonon anomaly was found as a linear dependence of the total number of valence electrons in Ni[sub x]Al[sub 1[minus]x] alloys.
- Research Organization:
- Iowa State Univ. of Science and Technology, Ames, IA (United States)
- OSTI ID:
- 7003445
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Theoretical study of electron-phonon interaction in [beta]-phase NiTi and Ni-Al alloys
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CRYSTAL-PHASE TRANSFORMATIONS
ELECTRON-PHONON COUPLING
ELECTRONIC STRUCTURE
NICKEL ALLOYS
TITANIUM ALLOYS
BAND THEORY
BINARY ALLOY SYSTEMS
LCAO METHOD
MARTENSITE
SLATER METHOD
THEORETICAL DATA
TITANIUM-BETA
ALLOY SYSTEMS
ALLOYS
CALCULATION METHODS
CARBON ADDITIONS
COUPLING
DATA
ELEMENTS
INFORMATION
IRON ALLOYS
METALS
NUMERICAL DATA
PHASE TRANSFORMATIONS
TITANIUM
TRANSITION ELEMENTS
665000* - Physics of Condensed Matter- (1992-)
360102 - Metals & Alloys- Structure & Phase Studies