Introduction

Abstract

Abstract A phase trans1t10n occurs when there is a singularity in the free energy or one of its derivatives. What is often visible is a sharp change in the properties of a substance. The transitions from liquid to gas, from a normal conductor to a superconductor, or from paramagnet to ferromagnet are common examples. The phase diagram of a typical fluid is shown in Fig. 1.1. As the temperature and pressure are varied water can exist as a solid, a liquid, or a gas. \Yell-defined phase boundaries separate the regions in which each state is stable. Crossing the phase boundaries there is a jump in the density and a latent heat, signatures of a first-order transition.