Order and Disorder in Condensed Matter. David Long Price, Argonne National Laboratory, Argonne, IL 60439, USA

Melting of a crystalline solid is generally thought of as a disordering process from a state in which the atoms execute thermal motions about static equilibrium sites to one in which all they migrate randomly over the whole space occupied by the material. In a complex system, several different components of this disordering may be distinguished: these can include translational disorder of one sublattice, chemical disorder between two or more sublattices, orientational disorder of molecules or complex ions, or lattice melting in one or two directions in the crystal. When such a system is heated towards the melting point, different dynamical disordering processes set in until complete long-range disorder is achieved in the liquid state, although a substantial degree of short- and intermediate-range order may be retained. On cooling, the ordered crystalline state may be regained, or a metastable state may be established in which some or all of the structural disorder is frozen in. Along with these changes in atomic structure and dynamics, variations in the transport properties and response functions of the systems, such as electronic conduction, thermopower, Hall effect, magnetic susceptibility and ionic conduction, may be expected. The lecture will summarize some of the varieties of order and disorder encountered in condensed matter and examples of physical properties affected.