Random Non-Random Periodic Fau PDF

FOREWORD

The crystallographic community is already indebted to Professor P. Krishna and his colleagues for several major works, including Polymorphism and Polytypism in Crystals (A. R. Verma & P. Krishna, 1966), and Crystal Growth and Characterization of Polytype Structures (edited by P. Krishna, 1983). More recently the Teaching Commission pamphlet Close-packed Structures has been expanded into an important chapter "Layer stacking in close-packed structures" in International Tables for Crystallography, Volume C (D. Pandey & P. Krishna, 1992). Now we welcome Random, Non-Random and Periodic Faulting in Crystals. These books are based not only on the original research of Professor Krishna and his colleagues but also on the works of many other researchers — about one thousand publications are cited in the present work.

As presented by the authors, the study of faulting in crystals by means of diffraction methods began with the almost simultaneous publication in 1942 of a paper by Hendricks & Teller and of another by myself (for details, see references 2 and 3 of chapter 3). Professor A. R. Verma took up the problem and, together with Professor Krishna, incorporated the idea of screw dislocations as well as faulting into the development of single crystals of poly types. Professor Krishna's PhD thesis (Banaras Hindu University, 1962) was the foundation for Polymorphism and Polytypism in Crystals. Further progress in the understanding of the mechanisms of production of poly types and faulting was provided by the "faulted-matrix m oder developed in conjunction with D. Pandey; Pandey also collaborated in writing two of the publications already mentioned. The present book results from collaboration with M. T. Sebastian. A glance at the Table of Contents will show its wide-ranging scope. The first two chapters are introductory, outlining the methods of experimental investigation, and the nomenclature and symbols used for describing the structures revealed by them. The three bulky remaining chapters are concerned with successively less tractable problems: (3) "Diffuse X-ray scattering from randomly faulted close-packed structures", (4) "Phasetransformations and non-random faulting in close-packed structures" and (5 ) "Periodic faulting in crystals". The varieties of silicon carbide (SiC) are a recurrent theme, with zinc sulphide (ZnS) perhaps taking second place, but no thoroughly investigated material is ignored. The contributions of Pandey and Sebastian to the work on SiC and ZnS, respectively, are noteworthy.

Chapters 3 and 4 on non-random faulting contain material not paralleled in any of the earlier books. The theory of diffraction by crystals with non-random faults goes back at least to the work of Landau and Lifschitz (Phys. Z. Sowjetunion 1 2 , 579-585, 623-643, 1937), which I have cited in various contexts. Although the basic theory is old, chapter 4 contains what is probably the first extensive experimental study of the diffuse intensity associated with the non-random faulting produced by phase transformations in the solid state, and thus sheds light on the mechanism of phase transformation.

It is not the province of the writer of a Foreword to offer only uncritical praise. I must cavil somewhat at the title, which invites us to a general treatment of imperfections in (approximately) dose-packed structures. In fact, the book is almost confined to layer structures, with onedimensional disorder, and mentions structures with three-dimensional imperfections only in passing. The latter are perhaps mainly of interest for the diffraction phenomena that they exhibit, rather than for their practical importance; for the non-theoretician this "imperfection" is more apparent than real.

This book is recommended to the crystallographic community for its clarity, thoroughness and coverage.

Author: M. T. Sebastian and P. Krishna