Character of order-disorder and displacive components in barium titanate.

Reconciling the apparently contradictory results of NMR and x-ray absorption fine structure measurements on the ferroelectric perovskite BaTiO3 gives insight into the character of the displacive and order-disorder components of the phase transitions of this material. The order-disorder component in the transition consists of local atomic displacements from cubic symmetry of constant magnitude that partially lose long-range order, while the displacive component consists of reorientation of these displacements.