As outlined above, perovskites form the most important class of
ferroelectric materials. They are named after the mineral perovskite
(it was discovered later that
shows only a distorted perovskite structure). The perfect structure
follows the formula
, where A is a mono- or divalent
and B is a tetra- or pentavalent metal [Die97]. As outlined in Fig. 2.3, the
A atoms form the corners of the 'cubic' cells, B atoms are in the center
and the oxygen atoms are situated in the faces' centers. As the B atoms are
enclosed in
octahedra, this structure is also regarded as
.