Basic Crystal Structure
A regular and repetitious pattern in which atoms of a crystalline material arrange themselves is known as the crystal structure.
A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way;
which is periodically repeated in three dimensions on a lattice.
In practical most of the metals crystallise in one of the three relatively simple structures
namely BCC, FCC, CPH or HCP.
This orderly and regular arrangement of the metal balls minimizes the empty space
between them. Closest packing is the most efficient arrangement of spheres. Atoms of a
metal crystal are arranged in similar patterns, called close-packed structures.
A unit cell is the most basic and least volume consuming repeating structure of any solid.
It is used to visually simplify the crystalline patterns solids arrange themselves in. When
the unit cell repeats itself, the network is called a lattice.
Miller indices, group of three numbers that indicates the orientation of a plane or set of
parallel planes of atoms in a crystal structure. The reciprocals of these intercepts are computed,
and fractions are cleared to give the three Miller indices (hkl).
Miller indices are used to specify directions and planes. These directions and planes
could be in lattices or in crystals. The number of indices will match with the dimension of
the lattice or the crystal.
Atomic packing factor (APF), packing efficiency, or packing fraction is the fraction of
volume in a crystal structure that is occupied by constituent particles. It is a dimensionless
quantity and always less than unity.
Coordination number, also called Ligancy, the number of atoms, ions, or molecules that a
central atom or ion holds as its nearest neighbours in a complex or coordination compound
or in a crystal.
Classification of common Crystal structure:-
3.Face Centered Cubic Structure(FCC)
In a hexagonal close-packed (hcp) arrangement of atoms, the unit cell consists of three layers of atoms. The top and bottom layers (a) contain six atoms at the corners of a hexagon and one atom at the center of each hexagon.
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