Crystallography - Basics

Crystallography is a branch of physics deals together with the learn of internal properties, structure, external or internal symmetries in a crystal. Reason is created of molecules or atoms and structure of atom atoms determines the reason of state. A reason shall be in 4 states: solid, liquid, gas and plasma. Kinetic Molecular Theory of Reason is one regarding the simple theories, which states that the atoms and molecules possess life of motion. The more life regarding the atoms creates more molecular movement regarding the atoms.

Solid state has fixed volume and shape. In solid state the atoms are in fixed positions in relation to one another. Solid particles also vibrate but still remains within the relative position. When they can be heated the atoms vibrate faster than in normal state. During heating all the solid structures grows slightly and this is called as expand.

All solid structures expand while heating mostly metals. If atom in a solid structures are arranged in a period sequence or systemic pattern are referred to as crystals. Salts and metal are crystalline and if the atoms arranged in irregular pattern or in haphazardly, then the solid is spoke about as amorphous. Amorphous solids are isotropic and homogeneous as there is no order or periodicity in their arrangement of internal atoms. Crystals are arranged in standard pattern and hence they can be anisotropic with varying properties in different direction.

A crystal has 3 dimensional and the atoms are represented as points in a standard pattern of crystal are called as space lattices. Unit cell is defined like a parallelepiped and the edges regarding the unit cell is formed by the lattice vectors namely a, be and c. Unit cell is a smallest geometric figure that is repeated to obtain the actual crystal structure and this is the fundamental elementary pattern for the minimum arrangement of atoms in a crystal. There are 3 variations of lattices called the Bravais and the non Bravais lattices. In Bravais lattice, all lattice points are equivalent and the atoms in a crystal are regarding similar kind.

In case of non Bravais lattices some lattice points are non-equivalent and they shall have combinations of 3 or more interpenetrating Bravais lattices together with the orientations fixed. Simple cubic system has one lattice spot each corner regarding the cube. Only metal reported to have this kind of cubic system is the polonium. Body centred cubic system has eight lattice points at the corners and apart from those one lattice spot within the centre regarding the cube. Face centred cubic has lattice points on the faces regarding the cubes and giving a total of 4 lattice points.

There are seven variations of crystal system based on the lattices points and they can be Triclinic, Monoclinic, Orthorhombic, Tetragonal, Rhombohedral, Hexagonal, and Cubic.