Sliding over a phase transition.

The effects of a displacive structural phase transition on sliding friction are in principle accessible to nanoscale tools such as atomic force microscopy, yet they are still surprisingly unexplored. We present model simulations demonstrating and clarifying the mechanism and potential impact of these effects. A structural order parameter inside the material will yield a contribution to stick-slip friction that is nonmonotonic as temperature crosses the phase transition, peaking at the critical T(c) where critical fluctuations are strongest, and the sliding-induced order-parameter local flips from one value to another more numerous. Accordingly, the friction below T(c) is larger when the order-parameter orientation is such that flips are more effectively triggered by the slider. The observability of these effects and their use for friction control are discussed, for future application to sliding on the surface of and ferro- or antiferrodistortive materials.