Martensitic Phase Transition in Systems with Frozen Atomic Order

Abstract

We study systems that can be described in terms of two kind of degrees of freedom when the corresponding ordering modes couple one to the other. The primary ordering mode gives rise to a diffusionless first-order phase transition and the secondary mode, that we suppose can be externally controlled, is associated to a continuous phase transition. Our interest is to analyze how the thermodynamic properties of the primary phase transition change as a function of the secondary ordering-mode. This can be experimentally realized in metallic alloys undergoing, at low temperatures, a martensitic phase transition and an order-disorder transition at much higher temperatures. In this case we obtain that, because of the directional character of the martensitic transition, the entropy-change dependence on atomic order is very small.