Chp. 3 Summary
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Atoms in crystalline solids are positioned in
orderly, repeated patterns. For nincrystaline or amorphous materials they are randon and disordered
Crystal structures are specified in terms of
parallelepiped unit cells, which are characterized by geometry and atom positions within.
The concept of crystal system is used to
classify crystal structures on the basis of unit cell geometry. (unit cell edge lengths and interaxial angles)
Name 7 Crustal systems
cubic, tetragonal, hexagonal, orthorhombic, rhombohedral (trigonal), monoclinic, and triclinic.
Crystallographic points in a unit cell is specified using
coordinates that are fractional multiples of the cell edge lengths.
Directional indices are computed in terms of
the vector projection on each of the coordinate axes.
Planar (or Miller) indices are determined from
from the reciprocals of axial intercepts.
What are Single Crystals?
materials in which the atomic order extends uninterrupted over the entirety of the specimen
Define polycryistalline
Solid being composed of many small crystals or grains having different crystallographic orientations.
Define anisotropy
the directionality dependence of properties. For isotropic materials, properties are independent of the direction of measurement.
Noncrystalline solids
lack a systematic and regular arrangement of atoms or ions over relatively large distances (on an atomic scale)