materials*

Abstract: The requirement for novel materials to perform in hostile environments to include high pressure and temperature is the driving force behind the push in research into advanced materials for engineering applications. To assess their usefulness, it is essential to know the thermodynamic properties of any new material. A complete thermodynamic characterisation must incorporate a determination of the thermophysical properties such as the heat capacity from which the enthalpy, entropy, free energy and structural information can be derived, the thermochemical properties such as enthalpies and free energies of formation, and the thermodynamic stability of the material. The thermodynamic properties of two main groups of materials will be reviewed in this plenary lecture, namely the solid transition metal silicides and the solid transition metal chalcogenides. The transition metal silicides are a well-defined family of compounds MaSib with the metal element M within groups 3 to 11 of the periodic table. Their high degree of stability, resistance to oxidation and great tensile strength, all properties at elevated temperatures, account for their desirability as engineering materials. The transition metal chalcogenides have a general formulation MX2, where M is a transition metal element and X is a chalcogenide specifically sulfur, selenium or tellurium. Virtually all members of this family of layered compounds are composed of a sheet of metal atoms sandwiched between two sheets of chalcogens. Their stability at high temperatures, ease of one layer sliding over adjacent layers, and their ability to allow intercalation by foreign atoms contribute to the demand for their use. It is not surprising that only limited thermodynamic information is available for these two families as the rapid pace in development of new materials is occurring at a rate faster than the experimentalists can determine their thermo-dynamic properties