The martensitic transformation in In-Tl alloys revisited

Full text: The traditional view for the martensitic transformation in In-xat%Tl alloys, for 15.5 ≤ 𝑥 ≤ 30.5 was via a double shear such as: (101) [101]; (011) [011], on the basis of optical microscopy observations and measurements of the (𝑐₁₁ - 𝑐₁₂)/2 elastic constant. However, this model was called into question following recent low-ζ measurements of the [ζζ0][ζζ0] phonons. An alternative model for the formation of coherent nuclei and growth along conjugate {111} planes was once proposed by Geisler. This model is consistent with some electron diffuse scattering data as well as yielding identical x-ray pole gure results as those for the double-shear mechanism. Appropriate nuclei could be generated by 111 112 atomic displacements. To test such an idea we have measured the [ζζζ]T phonon branch for a good quality In-Tl crystal in a recent experiment using the cold-triple axis facility, SIKA, at the OPAL Research Reactor. These results will be reported and compared with the predictions of a model for the dynamical behaviour of coherent interfaces and modulated structures based on topological solitons, first introduced by Barsch and Krumhansl and applied to the twins accompanying martensitic transformations. (author)