Thermal Design, 2nd Edition

6Thermoelectric Materials

6.1 CRYSTAL STRUCTURE

Although the symmetry and beauty of crystals have always excited curiosity and wonder, the science of crystallography did not begin until the latter part of the eighteenth century. In these closing days of the Age of Enlightenment, when Lavoisier led the modern approach to chemistry, another brilliant French thinker established the fundamental laws of crystallography. Réné Just Haüy was struck by the fact that when he accidently dropped a crystal of calcite (a form of calcium carbonate), it fractured into smaller crystals that had the same interfacial angles between their plane surface as did the original crystal. The consistency of the interfacial angles observed when crystals are cleaved is known as Haüy's law. Haüy drew the conclusion that the outward symmetry of crystals implies an internal regularity and the existence of a smallest crystal unit. The first experimental evidence for the periodicity of the structure was reported in 1912 by Laue using x‐ray diffraction by crystals. In the late 1990s, direct images of crystal structure have been produced by scanning tunneling microscopy (STM). One exploits the large variations in quantum tunneling as a function of the height of a fine metal tip above the surface of a crystal. The image in Figure 6.1 was produced this way. An STM method has been developed that will assemble single atoms into an organized layer nanometer structure on a crystal substrate.

6.1.1 Atomic Mass

The ...