What is a Unit Cell and How does Lattice Parameters Relate to them?
The unit cell is regarded as the basic “building block” of a crystal. It is a human construct used to simplify our notion about the size, location, and number of objects contained within the crystal. Pictorially, it is a parallepiped that has lengths and angles, known as the lattice parameters, that are the same as the characteristic angles and repeat distances within the crystal. Theoretically, we should be able to “construct” the entire crystal just by placing a large number of these unit cells next to each other in all directions. A valid unit cell should have a calculated mass density that is very similar to the actual experimentally determined density of the bulk crystal. The crystal structure of graphite has hexagonal symmetry. The unit cell for graphite can be reduced to a parallelpiped that has two characteristic sides whose length is equal to the “a” lattice parameter. The angle between these two sides measure 120 degrees. The repeat distance along its hexagonal axis is equal
