Some Lattice and Electronic Properties of the β-Tungstens

This chapter describes the work that has already been done, and also mentions work that is in progress, but is not as yet properly understood, in β-Tungsten research. Regarding work that has already been done, it is seen that elastic anomalies and martensitic phase transformations appear to be quite a general phenomenon; they require a large deformation potential, a large electronic density of states at the Fermi level (that may result from Van Hove singularities), and a degeneracy of the electronic states (with the same value of k, or with different ones). To a certain extent, they can be described by the Landau theory of order-disorder transformation, but most commonly they may be expected to be first-order transitions. The various microscopic models proposed so far to account for these anomalies; all predict a Landau type behavior. Therefore, this behavior is not a test for the applicability of one or another of these models. Lattice instabilities due to optical phonons should also be present, but they have not been observed so far in the β-tungstens, except for Nb₃Sn, probably because they have not been looked for (except in V₃Si, where they are not present). They may be associated with sharp peaks in the ultrasonic attenuation as a function of temperature, such as those observed in V₃Ge.