Elastic and thermodynamic properties of the shape-memory alloy AuZn

This work reports the elastic shear moduli, internal friction, and specific heat of the B2 cubic ordered alloy AuZn as functions of temperature, Measurements were made on single-crystal and polycrystalline samples using resonant ultrasound spectroscopy, semiadiabatic calorimetry and quasistatic stress-strain measurements. Our results confirm that this alloy exhibits the shape-memory effect and a phase transition at 64.8 K that appears to be second-order (continuous) from the specific heat data. The acoustic dissipation does not peak at the transition temperature as expected but instead rises well into the low-temperature phase. The low-temperature limiting Debye temperature value Theta(D) = 219 K, obtained from a linear fit of C/T versus T-2 from T = 0.59 K to T = 5.3 K is in favourable agreement with the value calculated from the acoustic data Theta(D) = 207 K, using a T = 0 linear extrapolation of the shear moduli. It is argued that the combination of equiatomic composition and a low transformation temperature constrain the chemical potential and its derivatives to exhibit behaviour that lies at the borderline between that of a first-order (discontinuous) and a continuous phase transition.