What is Crystal?

Crystal is any solid material in which the component atoms are arranged in a definite pattern and whose surface regularity reflects its internal symmetry.

A crystal structure is formed only when the group of atoms is arranged identically at the lattice point. The group of atoms or molecules is called a basis. Lattice point is actually an imaginary concept. Periodic arrangement of infinite point on a plane without atoms is called lattice. When we place identical groups of atoms into lattice then it is called basis.

 In other way we can say that-

                                                          basis + lattice = crystal.

Line joining any two points is a translation in lattice. Two non-collinear translation leads to plane lattice and three non-coplanar translation leads to a space lattice.

If a liquid is allowed to cool slowly, the molecules will arrange themselves in an orderly manner and this will finally result in a crystalline solid.

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Solid materials and their types

What is solid?

Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice (crystalline solids, which include metals and ordinary ice) or irregularly (an amorphous solid such as common window glass).

Solid materials may be three types according to order region:

Amorphous: are the materials having order only within a few atomic or molecular dimensions. 

Polycrystalline: are the materials having some order regions called crystalline grains. The grains can be more or less aligned w.r.t. each other. Where they meet is called grain boundary.

Single-crystal: are the materials having a high degree of order or regular geometric periodicity throughout the entire volume of the material.

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