Theoretical study of electron-phonon interaction in [beta]-phase NiTi and Ni-Al alloys

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7003445

Zhao, G L

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
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
665000* -- Physics of Condensed Matter-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOY SYSTEMS
ALLOYS
ALUMINIUM ALLOYS
BAND THEORY
BINARY ALLOY SYSTEMS
CALCULATION METHODS
CARBON ADDITIONS
COUPLING
CRYSTAL-PHASE TRANSFORMATIONS
DATA
ELECTRON-PHONON COUPLING
ELECTRONIC STRUCTURE
ELEMENTS
INFORMATION
IRON ALLOYS
LCAO METHOD
MARTENSITE
METALS
NICKEL ALLOYS
NUMERICAL DATA
PHASE TRANSFORMATIONS
SLATER METHOD
THEORETICAL DATA
TITANIUM
TITANIUM ALLOYS
TITANIUM-BETA
TRANSITION ELEMENTS