Physics Of Crystals

Phase transitions in which crystalline solids undergo structural changes present an interesting problem in the interplay between the crystal structure and the ordering process. This text, intended for readers with some prior knowledge of condensed-matter physics, emphasizes the basic physics behind such spontaneous structural changes in crystals. Starting with the relevant thermodynamic principles, the book discusses the nature of order variables and their collective motion in a crystal lattice; in a structural phase transition a singularity in such a collective mode is responsible for the lattice instability, as revealed by soft phonons. This mechanism is analogous to the interplay of a charge-density wave and a periodically deformed lattice in low-dimensional conductors. The text also describes experimental methods for modulated crystal structures and gives examples of structural changes in representative systems. The book is divided into two parts. The first, theoretical, part includes such topics as: the Landau theory of phase transitions; statistics, correlations and the mean-field approximation; pseudospins and their collective modes; soft lattice modes and pseudospin condensates; lattice imperfections and their role in the phase transitions of real crystals. The second part discusses experimental studies of modulated crystals using x-ray diffraction, neutron inelastic scattering, light scattering, dielectric measurements, and magnetic resonance spectroscopy.

Research in solid-state physics in general and in the physics of dielectrics in particular has grown rapidly in scope and quan­ tity in the last twenty-five years. In the fifties and early sixties, there was an upsurge of interest in ferroelectricity, piezoelectrici­ ty, and pyroelectricity. The classical physics of dielectrics, rep­ resented by books of H. Frohlich, C. P. Smyth, G. I. Skanavi, and A. von Hippel, is now unthinkable without ferroelectricity. The structure and properties of ferroelectrics have been described in a number of books and reviews, including those of W. Kanzig, H. D. Megaw, F. Jona and G. Shirane, W. J. Merz and E. Fatuzzo. The present work deals with the physics of crystalline di­ electrics and is based on the investigations carried out by scien­ tists throughout the world. But, understandably, the emphasis is on the research done in the USSR, particularly in the author's labo­ ratory. A special feature of this two-volume treatise is the pro­ minent place given to the symmetry and structure of dielectrics and to the importance of spontaneous electric polarization in many properties of crystals. In fact, these aspects take up the whole of the first volume. The second volume is concerned mainly with various properties and phenomena whose nature is illustrated by considering specific crystals. Thus, for example, the phenomena of polarization, piezoelectricity, electrostriction, etc. , are first discussed in detail. Then follow descriptions of these phenomena in specific compounds.