ATOMIC DISPLACEMENT RELATIONSHIP TO CURIE TEMPERATURE AND SPONTANEOUS POLARIZATION IN DISPLACIVE FERROELECTRICS

The phase transition from nonpolar to polar in displacive ferroelectric crystals is accompanied by the displacement z of certain atoms from their higher-temperature symmetry positions. A study of all displacive ferroelectrics in which atomic positions have been determined has shown that a fundamental relationship exists between z and the Curie temperature TC. This relation has been form TC=(K2k)(z)2, where K has the dimensions of a force constant, k is Boltzmann's constant, and TC is in absolute units. A least-squares fit, based on z and TC for ten different ferroelectrics, gives K2k=(2.000.09)×104°K -2. In addition, the spontaneous polarization Ps is found to be related to z by the equation Ps=(2589)z C cm-2. K is discussed in terms of the interatomic force constant along the polar axis. © 1968 The American Physical Society.