Observation of a continuous phase transition in a shape-memory alloy

Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and pressure-dependent electrical transport measurements have been made on single crystals of AuZn and Au(0.52)Zn(0.48). Elastic neutron scattering detects new commensurate Bragg peaks (modulation) appearing at Q = (1.33, 0.67, 0) at temperatures corresponding to each sample's transition temperature (T(M) = 64 and 45 K, respectively). Although the new Bragg peaks appear in a discontinuous manner in the Au(0.52)Zn(0.48) sample, they appear in a continuous manner in AuZn. Surprising us, the temperature dependence of the AuZn Bragg peak intensity and the specific-heat jump near T(M) are in favorable accord with a continuous transition. A fit to the pressure dependence of T(M) suggests the presence of a critical end point in the AuZn phase diagram located at T(M)* = 2.7 K and p* = 3.1 GPa.