Colloquia

Equilibrium states of matter balance the thermodynamic tendency to minimize energy with the simultaneous need to maximize their entropy. Depending on the temperature, different equilibrium states may occur representing different tradeoffs between energy and entropy, leading potentially to a multiplicity of solid state phases. The phase diagram of a superalloy and of the element Pu illustrate the importance of entropy residing in modes of atomic vibrations. Additional examples will be given of quasicrystal- and glass-forming alloys in which the entropy resides instead in novel discrete configurational degrees of freedom.