The Shell Model and Interatomic Potentials for Ceramics

Abstract

In a classification of solids according to their bonding character (into metals, ceramics and glasses, polymers, and semiconductors), the ceramic class includes an enormous range of industrially important materials. From the archetypal ionic solids through oxides to silicates, and to covalently bonded materials such as SiC, they exhibit a rich variety of structures and properties. They occur as structural materials, either on their own or as composites such as SiC/Al2O3. They are important functional materials, such as fast-ion conductors as electrolytes in fuel cells (for example ZrO2/Y2O3 for hydrogen combustion) or batteries (β-alumina in the sodium-sulfur battery), ferroelectric materials such as BaTiO3 and piezoelectrics such as PZT—a solid solution of PbTiO3 and PbZrO3. The high-temperature superconductors (for example, YBa2Cu3O7) are ceramics above the superconducting transition temperature. The products of corrosion and oxidation are ionic materials, and the properties of oxide coatings are vital to the survival of high-temperature alloys in gas turbines or fuel-element claddings in nuclear reactors.To understand the behavior of ceramic materials, and to optimize their production, processing, and application, it is often necessary to model their behavior at an atomic level. In some cases this is obvious. Ionic diffusion in a solid electrolyte is a self-evidently atomic process. In other cases the need for atomistic simulation is less clear. Oxidation, for example, is a subtle blend of atomic diffusion (often along grain boundaries), metal-ceramic bonding, stress relief, and grain growth. The course of oxidation can be spectacularly affected by impurities and alloying, and this can only be understood by considering the atomicscale processes involved.