Ferroic materials

Understanding the significant alterations in physical properties that take place within a relatively limited temperature range is the foundation of ferroics. When phase transitions take place around a critical temperature value, which is often shown by the displaystyle T cT c, the physical features alter. The crystal is in a nonferroic state above this critical temperature and does not display the desired physical property. When the material is cooled down below displaystyle T c T c, a spontaneous phase change occurs. In most cases, such a phase transition only slightly modifies the nonferroic crystal structure, but by changing the geometry of the unit cell, the material's point symmetry is compromised. Physically, the ferroic phase can develop because of this symmetry breach. In ferroelastic crystals, a spontaneous strain is created during the transition from the nonferroic (or prototypic phase) to the ferroic phase. When the crystal structure spontaneously transforms from a tetragonal structure (a square prism shape) to a monoclinic structure, this is an illustration of a ferroelastic phase transition (a general parallelepiped). In this case, a strain is produced inside the bulk as a result of the differing forms of the unit cell before and after the phase transition. A novel class of ferroic materials has recently attracted more attention. These multiferroics display many ferroic characteristics concurrently in a single phase.