Three basic types of crystals are:
1. Single Crystals
2. Poly Crystals
3. Liquid Crystals
1. Single Crystals: Those crystals in which patterns are regular throughout the whole crystal are known as single crystals. The variation in size of single crystals is from centimeter to few centimeters. Some single crystals are of very small sizes. Those small sized crystals are known as mono crystals. The approximate size of a mono crystal will be nearly 5×10-4, if it consists of nearly 104 unit cells. Most of the single crystals have different refractive index, electrical conductivity as well as mechanical strength different in all directions. This is also known as the anisotropic behavior of the crystals.
2. Polycrystals: If all the well maintained faces of the mono crystals are combined together then the resultant crystal formed is known as polycrystal. The process of making a polycrystal is not so easy. Lots of precautions are needed to form a polycrystal. Isotropic properties are shown by most of the polycrystals. But the mono crystals which are combined to form polycrystals are of anisotropic behavior. Ceramics are the main example of the polycrystals. Telephone receivers and gas lighters are made with the help of ceramics. Ceramics are bad conductors of electricity. But if these are mixed with some substances like Bao, CuO2 etc then these become superconductors.
3. Liquid crystals: Liquid crystals are not found in purely liquid form. These are basically fluids between the solids and liquids, which are formed upon heating some organic crystalline solids.
The orientation order in liquid crystals is of long order. Esters, cholesterol are some of the examples of the liquid crystals. These substances show a color change as the temperature changes. This property of the liquid crystals helps to calculate the temperature. The major use of these liquid crystals is in L.C.D’s. Now a day’s these crystals are commonly used in clocks, electronic watches etc.
