Transcription of Section 1: Crystal Structure
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Section 1: Crystal Structure
Physics 927 1 Section 1: Crystal Structure A solid is said to be a Crystal if atoms are arranged in such a way that their positions are exactly periodic. This concept is illustrated in using a two-dimensional (2D) Structure . A perfect Crystal maintains this periodicity in both the x and y directions from - to + . As follows from this periodicity, the atoms A, B, C, etc. are equivalent. In other words, for an observer located at any of these atomic sites, the Crystal appears exactly the same. The same idea can be expressed by saying that a Crystal possesses a translational symmetry. The translational symmetry means that if the Crystal is translated by any vector joining two atoms, say T in , the Crystal appears exactly the same as it did before the translation.
Wigner-Seitz primitive cell. All the space of the crystal may be filled by these primitive cells, by translating the unit cell by the lattice vectors. y x a1 a2 a T Fig.4 . Physics 927 E.Y.Tsymbal 3 The unit cell can be primitive and non-primitive (or conventional). The unit cell discussed above is
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