Very Low Thermal Expansion Coefficient Materials

Materials science treats the relations of composition and structure, on the one hand, to properties. On the other hand, the task of materials engineer­ ing is to design, evaluate, and optimize potential applications of a (new) material. In the last four decades dramatic advances have demonstrated how far our understanding of materials science and engineering has enabled us to design and bring into use a whole range of new devices based on materials in the field of monatomic and compound semiconductors. Unfortunately, this level of detailed knowledge and of control of the synthesis capacity is unique to the semiconductor field. In most of the materials fields our knowledge is not sufficient to develop a new material. Nevertheless, alJ such understanding is helpful in trying to develop a rational theory for the next generation of materials. In this review we treat a much neglected property of most materials­ the coefficient of thermal expansion-where the level of materials science is much more primitive. The relation of the property of thermal expansion to composition and structure eludes us, especiaIJy in the anomalously low thermal expansion materials in which there is the greatest interest. Very low expansion materials are not only important for practical uses but are also interesting scientifically. In the materials research and ceramic indus­ try the importance of the low thermal expansion materials is manifested in their widespread use in high anti thermal shock applications (cookware for oven to freezer use), electronic devices, heat-engine components, auto-