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Description of  Semiconductors: Physics of Semiconductors (Learn Physics Book 29)

Solids It is a state of matter which has a definite shape and a definite volume. The characteristic properties of the solid depends upon the nature of forces acting between their constituent particles (i.e. ions, atoms or molecules). Solids are divided into two categories. Crystalline solids (1) These solids have definite external geometrical form. (2) Ions, atoms or molecules of these solid are arranged in a definite fashion in all its three dimensions. (3) Examples : Quartz, calacite, mica, diamond etc. (4) They have well defined facets or faces. (5) They are ordered at short range as well as at long range. (6) They are anisotropic, i.e. the physical properties like elastic modulii, thermal conductivity, electrical conductivity, refractive index have different values in different direction. (7) They have sharp melting point. (8) Bond strengths are identical throughout the solid. (9) These are considered as true solids. (10) An important property of crystals is their symmetry. Amorphous or glassy solids (1) These solids have no definite external geometrical form. (2) Ions, atoms or molecules of these solids are not arranged in a definite fashion. (3) Example : Rubber, plastic, paraffin wax, cement etc. (4) They do not possess definite facets or faces. (5) These have short range order, and there is no long range order. (6) They are isotropic. (7) They do not have a sharp melting point. (8) Bond strengths vary. (9) These are considered as pseudo-solids or super cooled liquids. (10) Amorphous solids do not have any symmetry.