Curie principle[′kyu̇r·ē ‚prin·sə·pəl]
a postulate that permits the determination of the symmetry of a crystal subjected to an external perturbation (mechanical, electrical, or other). It was formulated by the French physicist P. Curie in 1894.
According to the Curie principle, a crystal changes its symmetry under an external perturbation in such a way that only those elements of symmetry are preserved that are common to the elements of symmetry of the perturbation. The principle becomes clear if one imagines that on a figure having the symmetry of the crystal there is superimposed in some way another figure, which has the symmetry of the perturbation. The figure resulting from such a superposition retains only those elements of symmetry that are common to the initial figures. For example, cubic crystals that do not have the property of birefringence acquire a lower degree of symmetry and become birefringent when they are placed in an electric field or in a field of mechanical stresses. The Curie principle also makes it possible to determine the change in the symmetry of a crystal during a phase transition from the symmetry of the new physical properties generated by the transition.
REFERENCENeye, J. Fizicheskie svoistva kristallov i ikh opisanie pri pomoshchi ten-zorov i matrits. Moscow, 1967. (Translated from English.)
N. V. PERELOMOVA