Bravais Lattices – The ‘Body-Centred’ Monoclinic Lattice
Two more lattice point settings are common in crystallography. These are body-centred and face-centred. Body-centred refers to lattice points at the vertices and also at the centre of the parallelepiped. This is shown in a 2D representation on the left below, examined by looking down the b axis. On the right, the lattice point arrangement is shown. In orange, a new possible unit cell is highlighted. Compare this with the base-centred unit cell on the previous page. This orange unit cell is also a base-centred monoclinic unit cell. As such, a body-centred monoclinic unit cell is actually a different representation of the base-centred monoclinic lattice. Remember, we have placed no restrictions on lattice parameters except \(\alpha = 90^{\circ}\) and \(\gamma = 90^{\circ}\).
Face-centred refers to lattice points arranged on every face of the parallelepiped. Below is the face-centred monoclinic unit cell viewed along the b axis. Have a go at drawing out multiple of these unit cells and the resulting lattice points on paper. Identify the base-centred monoclinic unit cell within this lattice point arrangement. The answer(s) are on the next page.
