Anomalous system-size dependence of properties at the fragile-to-strong transition in a bulk-metallic-glass forming melt

As many other glass formers do, bulk-metallic-glass (BMG) forming melts undergo a fragile-to-strong transition (FST), which is accompanied by a small but noticeable peak in the specific heat cp. Because of this peak, the FST is sometimes interpreted as a smeared-out phase transformation. Finite-size scaling analysis of peaks in cp allows the order of a phase transition to be accurately determined. This motivated us to study cp along with structural and dynamical properties of a ternary BMG former (Zr0.606Cu0.29Al0.104) using computer simulations, in which the system size was varied in a well-controlled fashion. Our model system reproduces the typical, almost discontinuous cross-over between non-Arrhenius to Arrhenius-type dynamics, which defines the FST. However, in contrast to the expectations for a phase transformation, the larger the system the smaller the peak in cp. Other properties also reveal a size dependence, which is difficult to reconcile with the interpretation of the FST being a (smeared-out) phase transformation resulting from the competition between different local structures.