Structural Phase Transitions I

1. Introduction.- References.- 2. Optical Studies of Structural Phase Transitions.- 2.1 Background.- 2.1.1 Phase Transitions in Solids: Definitions.- 2.1.2 Symmetry Classification of Optical Techniques.- 2.2 Experimental Techniques.- 2.2.1 Absorption and Fluorescence.- a) IR Absorption and Reflection.- b) Optical Absorption and Fluorescence.- 2.2.2 Birefringence.- a) Typical Experimental Apparatus.- 2.2.3 Light Scattering.- a) General Background.- b) Scattering from Coupled Modes.- c) Critical Exponents and Soft Mode Spectra.- d) Intensity of Scattering.- e) Grating Spectroscopy.- f) Interferometry.- g) Recent Advances of Technique.- 2.3 Ferroelastic Transitions.- 2.3.1 Cooperative Jahn-Teller Systems.- 2.3.2 PrAlO3: A Prototypical CJT System.- 2.4 Nonpiezoelectric Ferroelectric: Pb5Ge3O11.- 2.5 Piezoelectric-Ferroelectric Transition in KDP and Its Isomorphs.- 2.5.1 Coupled Modes i n the Raman Spectrum.- 2.5.2 Brillouin-Raman Spectra.- 2.5.3 Static and Dynamic Central Peaks.- 2.6 Zone Boundary Phase Transitions (Antiferrodistortive).- 2.6.1 Systematics in the Fluoroperovskites.- 2.6.2 Recent Results in SrTiO3.- 2.7 Zone Boundary Ferroelectrics: The Molybdates.- 2.8 Incommensurate Phase Transitions.- 2.8.1 Charge-Density Waves: TaSe2.- 2.8.2 Incommensurate-Ferroelectric: K2SeO4.- 2.8.3 Ferroelectric-Antiferroelectric: BaMnF4.- 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.- 3.1.1 General Aspects.- 3.1.2 Structural Changes with Small Displacements.- 3.1.3 Soft Modes.- 3.2 The Central-Peak Phenomenon.- 3.3 Molecular Crystals.- 3.3.1 The Elastic Incoherent Structure Factor (EISF).- 3.3.2 High-Resolution Instruments.- a) The Backscatteri ng Spectrometer.- b) The Four Chopper Time-of-Flight Spectrometer.- c) The Neutron Spin-Echo Spectrometer.- 3.3.3 Dynamics of Molecular Crystals.- a) Librations.- b) Rotational Reorientation of a Single Molecule.- c) Translational Lattice Vibrations.- d) Soft Modes and Relaxation of Clusters.- 3.4 Incommensurable Structures.- 3.4.1 Amplitude and Phase Modes.- 3.4.2 Conducting Materials.- 3.4.3 Insulating Materials.- References.- Additional References with Titles.- 4. Ultrasonic Studies Near Structural Phase Transitions.- 4.1 Background Material.- 4.1.1 Elastic Response Functions and Their Measurement.- a) Pulse Method.- b) CW Methods.- c) Low-Frequency Methods.- 4.1.2 Connection to Processes Characterizing the Phase Transition.- 4.2 Theoretical Analysis.- 4.2.1 Landau Theory.- 4.2.2 Symmetry Aspects.- 4.2.3 Mode-Mode Coupling and Scaling.- 4.2.4 Renormalization Group Analysis.- 4.3 Experimental Results.- 4.3.1 Strain Is Order Parameter.- a) Ferroelectrics.- b) Other Nonelectronic Compounds.- c) Cooperative Jahn-Teller Transitions.- d) Band Jahn-Teller Transitions.- e) Mixed Valence Transitions.- f) Martensitic Phase Transformations.- 4.3.2 Strain Is Not Order Parameter.- a) Phonon Coordinate Is Order Parameter.- b) Electric Polarization Is Order Parameter.- c) Orientational Degree of Freedom Is Order Parameter.- d) Charge-Density Wave Transitions.- e) Solid Electrolytes.- f) Incommensurate Phases.- 4.4 Summary.- References.- Additional References with Titles.