The basis of ferroics is to understand the large changes in physical characteristics that occur over a very narrow temperature range. The changes in physical characteristics occur when phase transitions take place around some critical temperature value, normally denoted by T c . Above this critical temperature, the crystal is in a nonferroic state and does not exhibit the physical characteristic of interest. Upon cooling the material down below T c it undergoes a spontaneous phase transition. Such a phase transition typically results in only a small deviation from the nonferroic crystal structure, but in altering the shape of the unit cell the point symmetry of the material is reduced. This breaking of symmetry is physically what allows the formation of the ferroic phase.