Chemical Basis of the Tribological Properties of AgTaO3 Crystal Surfaces

The chemical properties of a surface determine the friction and wear behavior of a material during sliding. In this article, we study the mechanisms underlying the sliding behavior of the AgTaO3 perovskite material, a promising high-temperature solid lubricant that presents excellent friction properties and is chemically inert. In particular, by employing a combination of molecular dynamics simulations and density-functional theory calculations, we show that the low friction of AgTaO3 at high temperature is explained by silver aggregation on the surface, which is enabled by the low energy barriers associated with silver migration. Two different surface terminations (Ago and TaO2) are studied, and we show that the migration barrier on the Ago surface is smaller, favoring silver aggregation, which affects both friction and wear. Regardless of the termination, the formation of soft silver clusters dominates the sliding behavior when enough energy (mechanical or thermal) is imparted to the surface.