Body-Centered Cubic (bcc)

Definition - What does Body-Centered Cubic (bcc) mean?

Body-centered cubic (bcc or cB) is a type of crystal structure in metals. This structure can be seen as a gathering of cubes with atoms at the edges and an atom in the center of every cube. The corner or edge atoms are shared among eight unit cells.The metals which have a bcc structure are:

  • Alpha iron
  • Tungsten
  • Chromium
  • Beta titanium

The elements which crystallize in the bcc structure show properties of metallic conductors. They have the eight-fold coordination in the nearest neighbor shell which does not permit saturated bonds.

Corrosionpedia explains Body-Centered Cubic (bcc)

The bcc structure has neither a stacking sequence nor stacking faults. Therefore, it does not have closed-packed planes. Its coordination number is eight. The bcc unit cell is comprised of a net total of two atoms. The packing factor of a bcc unit cell is 0.68. The packing factor is the volume of atoms in a cell per the total volume of a cell.

Simple metals and transition metals are crystallized in the bcc structure:

  • Simple metals like sodium, potassium, rubidium and calcium have simple metallic bonding.
  • Transition metals like titanium, molybdenum, tungsten and iron have some contribution to the bonding from the d-electrons. The d-electrons occupy unfilled orbitals in the ion core. The symmetry of d-bonding facilitates the bcc structure.

Bcc structure metals are generally harder and less malleable than close-packed metals such as gold. In deformed metals, the planes of atoms slip over each other, and this is quite difficult in the bcc structure metals. Some bcc materials can contain up to 48 slip systems like ferrite. A bcc slip system cannot activate without heat.

In a bcc structure, interstitial voids are crucial both as sites for solute atoms and as atom positions in interstitial compounds. The defective geometry of the interstitial voids causes important properties of the bcc materials that hold solutes in interstitial sites.

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