J. Phys. IV France 112 (2003) 1095
The martensite phase of high-purity lithiumW. Pichl1, M. Krystian1, M. Prem2 and G. Krexner3
1 Institut für Materialphysik, Universität Wien, Boltzmanngasse 5, 1090 Wien, Austria
2 Laboratoire Léon Brillouin, Centre d'Études Nucléaires de Saclay, 91191 Gif-sur-Yvette, France
3 Institut für Experimentalphysik, Universität Wien, Boltzmanngasse 5, 1090 Wien, Austria
The low-temperature martensitic transformation of pure lithium is characterized by a complex phase diagram exhibiting the coexistence of several close-packed phases with the bcc matrix. On cooling, below the martensitic start temperature a long-range ordered 9R structure and a one-dimensionally disordered polytype phase are observed. On heating, an intermediate fcc phase appears in the hysteresis regime. Microstructure investigations, application of the crystallographic theory of martensite and thermal cycling during neutron scattering experiments together strongly indicate that fcc is the true thermal equilibrium phase. The 9R structure is a metastable phase which minimizes the lattice mismatch with respect to the bcc matrix and therefore is formed for geometrical reasons.
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