INFLUENCE OF SMALL UNIAXIAL STRAINS ON THE MARTENSITIC PHASE-TRANSITION IN ALKALI-METAL SYSTEMS

A neutron scattering investigation of the influence of a uniaxial elas tic deformation on the martensitic phase transformation in the alkali- metal systems Li and Li10 at.%Mg is described. The experimental result s show that a small but symmetry-breaking elastic deformation of the b cc matrix drastically promotes the phase transformation. The deformati on further induces a significant reduction of the otherwise large tran sformation hysteresis in a vir in crystal and leads to a memory effect ; i.e., the hysteresis remains small when the applied elastic strain i s released. Moreover, the applied deformation of about 0.1% of the lat tice parameter induces a softening of the transverse acoustic TA(1)[11 0] phonon branch of several percent. The results are compatible with a description of martensitic nucleation in alkali metals as being trigg ered by strain fluctuations.