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Unformatted text preview: Lecture 1 Go over the description, outlining what topics it is hoped to cover Give some general idea of what each part will be Discuss the references, and mention differences between this year and previous years Survey the class to find out what they know Discuss the question of opting out of the class if the students have had the material before Overview The focus of this class is imperfections in crystalline materials in a broad sense. The class will not cover all possible examples, but instead will try and give a more general coverage. Relatively little will be said about defects in polymers or biomaterials, unfortunately. Instead the major areas will be metals, ceramics and semiconductors and applications will be (briefly) mentioned for as wide a range of properties as possible (and as I remember to mention them). To give a broad-base, not fully accurate sense of context, Physics: Often concerns itself with the average properties of materials, often perfect crystals. Chemistry: Often concerns itself with how to make different materials Materials Science: The relationship between micro and nanoscale structure, processing and properties. As such we are often interested in how defects change/affect the perfect crystal (physics) properties as well as how processing (chemistry) changes the defects. In many, many cases defects, rather than the perfect crystal properties determine the properties. (Note: you still need to understand the perfect crystal properties, i.e. 405, since this is the basic background. Similarly you need to understand the basics of thermodynamics etc since these govern how one reaches a particular micro/nano structure.) As a basic introduction, it is useful to go over the classes of defects. (Diagrams will be drawn in the lecture and are not included here.) Types of Defects 0D: Point Defects, e.g. interstitial, vacancy, substitutional defects, adatoms at surfaces 1D: Dislocations, disclinations (important in polymers and some models of polycrystalline materials), surface steps, some types of defect clusters such as crowdions 2D: Grain boundaries, Stacking Faults, interfaces between two different materials, surfaces, antiphase boundaries, some classes of chemical defects 3D: Precipitates, voids Examples of how defects can control properties: Mechanical Properties Most mechanical properties (not all) are determined by how easy it is for dislocations and/or point defects to move in a material. Magnetic Properties When one changes the polarity of an applied magnetic field, regions with the magnetism in one direction (almost magnetic grains, called domains) change to having the magnetism in another direction. This is normally done via the migration of the boundary between different magnetic domains. Defects can retard this motion so one can have hard (difficult to move the domains) or soft (easy to move the domains) magnetic materials....
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This note was uploaded on 04/13/2010 for the course MAT SCI 404 taught by Professor Matsci during the Winter '10 term at Northwestern.
- Winter '10