Electromagnetic properties of eutectic composites (A critical review)
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IYXETALS used in technological applications are generally composed of several elements and often there are also several phases present. By appropriate thermal and mechanical treatment one obtains the desired mechanical or magnetic properties. Metal single crystals are mainly used only for pure scientific research. In the case of semiconductors, however, the invention of the transistor and the discovery of the III-V compounds twenty years ago introduced a decade of semiconductor physics and technology in which all interest was concentrated on the perfect and pure single crystal which, with its regular array of one type of atom in elementary semiconductors and two or three types in compound semiconductors, also seemed to be the best starting material for devices. By doping, alloying, and diffusion it was possible to produce predetermined impurity profiles for the various kinds of diodes, transistor and thyristor, that is for the most important semiconductor devices. However, at the beginning of the aforementioned semiconductor decade there was already one type of semiconductor crystal in which the regular array of atoms had to be as strongly disturbed as possible: materials for thermoelectric devices having low thermal conductivity owing to mixed crystal formation with statistically distributed, and thus nonperiodic lattice distortions. As the example of thermoelectric materials shows, the ideal crystal does not always have the most favorable properties for applications in the case of semiconductors either. It was found that other solid-state structures may exhibit novel effects. Heavily doped crystals were therefore studied and interest a r o s e in a m o r p h o u s s e m i c o n d u c t o r s , w h i c h i n c l u d e v i t r e o u s s u b s t a n c e s . It w a s r e c o g n i z e d t h a t t h e r e exists no homogeneously-doped semiconductor and that inhomogeneities do not necessarily produce undesirable e f f e c t s . If t h e y a r e p r o d u c e d in a s u i t a b l e way, n o v e l electrical, optical, thermal, and magnetic properties c a n b e o b t a i n e d . I n c l u s i o n s of a s e c o n d p h a s e a r e a H. WEISS is Department Manager of Solid State Systems in the Research Laboratories of Siemens Aktiengesellschaft, Munich, West Germany. This paper is based on an invited talk presented at a symposium on Properties of.Aligned Eutectic Composites sponsored by the IMD Composite Materials Committee held on October 13, 1969 at the Fall Meeting of The Metallurgical Society of AIME, in Philadelphia, Pa. METALLURGICAL TRANSACTIONS
special case of inhomogeneities. Such materials exhibit their most interesting properties, in the form of unidirectionally solidified eutectics. The ratio of the phase volumes does not then depend on the particular manufacturing procedure. If the electromagnetic characteristics of matrix and inclusions are widely different, new phenomena can be expected. This paper briefly reviews how the electromagnetic properties of eutectic composites containing metals, semiconductor
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