w1-2_BasicCrystallographyPart1

w1-2_BasicCrystallographyPart1 - BASIC CRYSTALLOGRAPHY –...

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Unformatted text preview: BASIC CRYSTALLOGRAPHY – short review Statements: 1) Every crystal is a periodic assembly of atoms or molecules arranged to fill space. 2) Perfect crystals are described by the underlying crystal structure . ⇒ General Problem that Crystallography attempts to solve: How to describe the different possible ways to fill space with atoms or sub- groups of atoms (molecules)? What is a crystal structure ? and How to describe it ? Crystal represents a periodic arrangement of atoms. … but how do we distinguish between different crystals? … use CRYSTAL STRUCTURE = LATTICE + MOTIF CS = L + M What is a lattice and what is a motif (basis)? Examples of “Crystals or crystal structures in spaces that have one, two and three dimensions: 1-D: R R R R R R R R R R R R r R r R r R r R r R r 2-D: R r R r R r R r R r R r r R r R r R r R r R r R R r R r R r R r R r R r r R r R r R r R r R r R R r R r R r R r R r R r r R r R r R r R r R r R R r R r R r R r R r R r r R r R r R r R r R r R H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W H M W So, the Motif is the grouping of atoms, molecules, ions that are decorating the regularly distributed lattice points of the space lattice. The motif of the crystal structure is the pattern of atoms that is repeated ad-infinitum with the periodicity described by the space lattice. Every lattice point is decorated by the motif of the crystal structure. Every lattice has the same environment as every other lattice point. All lattice points have identical surroundings. All lattice points are equivalent. Only points that have the same surroundings as all other equivalent points can be lattice points....
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This note was uploaded on 01/07/2011 for the course MEMS Mems1054 taught by Professor Wiezorek during the Fall '10 term at Pittsburgh.

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w1-2_BasicCrystallographyPart1 - BASIC CRYSTALLOGRAPHY –...

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