Neutron and X-Ray Scattering Studies of Ferroelectric Phase Transitions

摘要

The subject of ferroelectric type phase transitions is introduced by means of examples of two main classes (a) displacive transitions, e.g. KNbO sub 3 , and (b) order-disorder transitions, e.g. NaNO sub 2 . The significance of crystal structure and crystal dynamics (i.e. the phonon dispersion relations) for ferroelectric behaviour is emphasized. The chief methods for structure determination are x-ray and neutron diffraction, while the most powerful of all techniques for studying phonon properties is that of coherent inelastic neutron scattering. The most useful type of neutron spectrometer for phase transition studies, the triple axis crystal spectrometer, is discussed in detail. The history of the soft mode theory of displacive phase transitions, and its application to the antiferroelectric and 'almost ferroelectric' transitions in SrTiO sub 3 , provides an introduction to more recent developments in this area, including over-damped soft modes, central peaks and critical scattering, incommensurate phase transitions (e.g. K sub 2 SeO sub 4 ), amplitudons, phasons and finally solitions. The treatment throughout is descriptive and introductory, designed for graduate students. (Atomindex citation 15:019490)