Optical properties and electronic structures of B2 and B19{sup {prime}} phases of equiatomic Ni-Ti alloys
- Department of Physics, College of Natural Sciences, Hoseo University, Asan, 336-795 Choongnam (Korea)
- Ames Laboratory-U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)
The dielectric functions of equiatomic Ni-Ti alloys were measured by spectroscopic ellipsometry in the energy range of 1.5{endash}5.4 eV at {approximately}423 and at {approximately}25 K. The peak at {approximately}2.26 eV in the B19{sup {prime}} (monoclinic structure) optical conductivity spectrum has a slightly larger magnitude than in the B2 (cubic CsCl structure) phase, while the shoulder at {approximately}3.5 eV becomes weaker and almost indiscernible upon martensitic transformation. A new structure develops at {approximately}2.85 eV in the B19{sup {prime}} phase; however, it is also very weak. The band structures and the optical conductivity were calculated in both phases using the linearized-augmented-plane-wave method within the local-density approximation. {bold k} points near the {Gamma}-X-M plane in the B2 phase and the corresponding {bold k}-points in B19{sup {prime}} phase contribute significantly to all three structures. The difference between the two spectra is due to the transitions between the folded-back bands from the B2 phase because of the larger unit cell of the B19{sup {prime}} phase and the change in the electronic energy spectrum near the Fermi level. The overall optical properties of Ni-Ti alloys in the measured energy range are rather insensitive to the martensitic transformation because the states far from the Fermi level are mainly involved in the interband transitions. {copyright} {ital 1999} {ital The American Physical Society}
- OSTI ID:
- 295542
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 3 Vol. 59; ISSN PRBMDO; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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