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Full Description
During the last fifteen years the field of the investigation of glasses has experienced a period of extremely rapid growth, both in the development of new theoretical ap proaches and in the application of new experimental techniques. After these years of intensive experimental and theoretical work our understanding of the structure of glasses and their intrinsic properties has greatly improved. In glasses we are con fronted with the full complexity of a disordered medium. The glassy state is characterised not only by the absence of any long-range order; in addition, a glass is in a non-equilibrium state and relaxation processes occur on widely different time scales even at low temperatures. Therefore it is not surprising that these complex and novel physical properties have provided a strong stimulus for work on glasses and amorphous systems. The strikingly different properties of glasses and of crystalline solids, e. g. the low temperature behaviour of the heat capacity and the thermal conductivity, are based on characteristic degrees of freedom described by the so-called two-level systems. The random potential of an amorphous solid can be represented by an ensemble of asymmetric double minimum potentials. This ensemble gives rise to a new class of low-lying excitations unique to glasses. These low-energy modes arise from tunneling through a potential barrier of an atom or molecule between the two minima of a double-well.
Contents
Dynamical Theory of Optical Linewidths in Glasses.- 1. Introduction.- 2. Model Hamiltonian.- 3. TLS Line-Broadening Mechanism.- 4. Homogeneous Linewidth.- 5. Microscopic Theory.- 6. Conclusions.- Optical Spectroscopy of Ions in Inorganic Glasses.- 1. Introduction.- 2. Inorganic Glass Structure and Composition.- 3. Optical Properties of Impurity Centers in Inorganic Glass.- 4. Laser Spectroscopy of Ions in Glasses.- 5. Concluding Remarks.- Model Calculation of Optical Dephasing in Glasses.- 1. Introduction.- 2. The Model and its Hamiltonian.- 3. Optical Line Shape Calculated with Mori's Formalism.- 4. Guest Molecule Coupled to a Single TLS.- 5. Line Shape.- 6. Averaging over Two-Level Systems.- 7. Coupling of the Impurity to Several Two-Level Systems.- 8. Concluding Remarks.- Structural Relaxation Processes in Polymers and Glasses as Studied by High Resolution Optical Spectroscopy.- 1. Introduction.- 2. The' site-Memory' Function.- 3. The Non-Equilibrium Nature of Glasses and its Relation to Optical Properties.- 4. Dynamic and Adiabatic Optical Relaxation Processes.- 5. Reversibility and Irreversibility.- 6. The Residual Linewidth.- 7. Spectral Diffusion and Structural Relaxation: Model Description.- 8. The Logarithmic Decay Law and its Relation to Other Dispersive Time Dependencies.- 9. Experimental Investigation of Spontaneous Structural Relaxation Processes.- 10. Field Effects and Spectral Diffusion Phenomena.- Models for Reaction Dynamics in Glasses.- 1. Introduction.- 2. Relaxation Viewed as Chemical Reaction: the Kinetic Approach.- 3. A Parallel Relaxation Scheme: the Direct Transfer.- 4. Parallel-Sequential Schemes: Random Walks.- 5. Continuous-Time Random Walks (CTRW).- 6. Ultrametric Spaces (UMS).- 7. The Bimolecular Reactions A + A ? 0, A + B ? 0 (A0= B0).- 8. Conclusions.
