Monocrystal and Polycrystalline
Monocrystal is a crystal in which the ordered arrangements of the atoms or molecules extends throughout the piece of solid , irrespective of its size .
Polycrystal is a crystalline solid in which each piece of the solid has a number of monocrystals with developed faces joined together .
The polycrystal ceramic made from PbO , ZnO and TiO are used in gas lighters and telephone receivers .
Liquid Crystals
Some organic crystalline solid . when heated acquire fluidity but retain their anisotropic properties . They axe called liquid crystals .
Some liquid crystals like cyan biphenyl can change the plane of polarization of light and such Liquid Crystal Displays ( LCD ) are used in watches and micro calculators .
Crystal Lattice
A crystal is made up of a three- dimensional array of points such that each point is surrounded by the height bouring Points in an identical way . Such an array of points is known as bravais lattice or space lattice .
Unit cell is the smallest unit of the crystal lattice , repetition of which in three dimensions gives rise to crystal lattice .
The length of three sides of a unit cell are called Primitives or lattice constant represented by a , b , c . The angle between three crystallographic axis are called interfacial angles represented by
α , β and γ . The primitives and interfacial angles constitute the lattice parameters of a unit cell .
[ The cubic crystal may be of the form , simple cubic ( sc ) lattice , the body centred cubic ( bee ) lattice , the face centred Cubic ( fcc ) lattice .]