§06§ §16§The growth and maturity of research in structural phase transitions (SPT) make it an appropriate subject for the Topics in Current Physics series. The maturing pro cess is, however, by no means complete. New areas such as incommensurable SPT, quasi-low-dimensional systems, systems containing lattice disorder due to impuri ties or as mixed crystals, multicritical points, and quantum effects have recently come under focus. The understanding of the dynamics, be it microscopic soft-mode theory or critical dynamics, more specifically the central-peak problem, is also still quite incomplete. On the other hand, there are areas which are genuinely conso 1 ida ted. On the theoreti ca 1 s ide~ these concern symmetry properti es, Landau theory, and the application of static renormalization theory to critical phenomena. ,Also, the use of various complementary experimental techniques, with their specific merits, are well in hand. The field of STP's and of the various methods of investigation r §16§ange so widely that it appeared appropriate to invite a number of scientists to review their respective areas of experti se to which they have made s i gnifi cant contri butions. §04§1. Introduction.- References.- 2. Optical Studies of Structural Phase Transitions.- 2.1 Background.- 2.2 Experimental Techniques.- 2.3 Ferroelastic Transitions.- 2.4 Nonpiezoelectric Ferroelectric: Pb5Ge3O11.- 2.5 Piezoelectric-Ferroelectric Transition in KDP and Its Isomorphs.- 2.6 Zone Boundary Phase Transitions (Antiferrodistortive).- 2.7 Zone Boundary Ferroelectrics: The Molybdates.- 2.8 Incommensurate Phase Transitions.- 2.9 Nonlinear Optical Studies of Phase Transitions.- 2.10 Renormalization Group Theory and Multicritical Phenomena.- 2.11 Concluding Remarks.- References.- 3. Investigation of Structural Phase Transformations by Inelastic Neutron Scattering.- 3.1 Inelastic Neutron Scattering.- 3.2 The Central-Peak Phenomenon.- 3.3 Molecular Crystals.- 3.4 Incommensurable Structures.- References.- Additional References with Titles.- 4. Ultrasonic Studies Near Structural Phase Transitions.- 4.1 Background Material.- 4.2 Theoretical Analysis.- 4.3 Experimental Results.- 4.4 Summ §04§ary.- References.- Additional References with Titles.
