Close packed structures with bases refer to crystal structures that have a high packing density, where the atoms or ions are arranged in a closely packed manner with a base layer repeating in a specific pattern.
There are three types of close packed structures with bases: hexagonal close packing (HCP), cubic close packing (CCP), and body-centered cubic (BCC). HCP has an ABABAB... stacking sequence, CCP has an ABCABC... stacking sequence, and BCC has an ABC stacking sequence.
In HCP and CCP structures, the atoms/ions are arranged in a hexagonal pattern where each atom/ion has 12 nearest neighbors. In BCC structures, each atom/ion has 8 nearest neighbors arranged in a cubic pattern with an additional atom/ion at the center of the cube.
Close packed structures with bases have high packing densities, making them strong and stable. They also have high melting points and electrical conductivity due to the closely packed arrangement of atoms/ions.
Close packed structures with bases are found in many common materials such as metals, ceramics, and some polymers. They are used in various industries, including construction, electronics, and transportation, due to their strength, stability, and conductivity.