Book Review (2): Fundamentals of Powder Diffraction and Structural Characterization of Materials

In this publication Pecharsky and Zavalij aim to produce a text that will provide both undergraduate and graduate students with a thorough grounding in the practical aspects of powder diffraction, methods for structure solution from powder data, and in the technique of Rietveld refinement.

As such the book aims to cover material that might traditionally have been found in classics such as the texts by Klug and Alexander or Cullity, as well as introducing areas covered in more depth by specialist publications such as the IUCr monographs edited by Young and David/Shankland/McCusker/Baerlocher. The stated entry level is that of students with a "general scientific and mathematical background of the order of the first two years of a typical...college". The book is a well produced and well illustrated text and includes a CD featuring colour figures, the numerous data sets presented in the text and solutions to the end of chapter problems. The cover deserves special note being apparently inspired by Dali's depiction of Narcissus falling in love with his own reflection and metamorphing via an egg into a flower - represented here by an intermetallic compound seeing a diffraction pattern, transforming to a reciprocal lattice before becoming an inorganic mixed metal oxide!

Chapter 1, as is common with many texts, covers elementary aspects of symmetry in the solid state, though also includes a nice "taster" of more exotic aspects of symmetry such as incommensurate modulation and quasicrystals to whet the reader's appetite.

Chapter 2 (160 pages) is an ambitious attempt to cover the "Fundamentals of Diffraction" from the production and monochromatisation of x-rays, their detection, simple diffraction theory through to the intensity corrections required for analysing powder data. I must confess that this was by far my least favourite chapter of the book as I personally found the arrangement of material peculiar. For example, monochromators are described before the phenomenon of diffraction has been introduced. The geometry of diffraction is then described (pleasingly to me via use of the Ewald sphere), however there are then some 60 pages covering intensity corrections and powder peak shapes before structure factors are introduced. Whilst there is nothing inherently wrong with the material, I can't help feeling that the approach could be confusing to beginners. I also felt that the level at which diffraction is introduced might be slightly daunting to the stated target audience.

Chapter 3 covers "Experimental Techniques" starting with a historical description of powder diffraction methods and instrumentation before moving on to consider sample mounting and how to optimise hardware and data collection parameters. There is also a useful section on the safety aspects of using ionising radiation. Common errors such as an inappropriate choice of slit size for a given experiment are covered in depth. I did feel that there was rather too much overlap between some of this material and that covered in chapter 2, particularly regarding e.g. monochromators and the choice of slits/detector set ups for different experiments.

Chapter 4 describes the "Preliminary Data Processing and Phase Analysis" of materials and essentially deals with the "everyday" aspects of routine powder diffraction work including peak searching, peak profile fitting and phase identification - in essence the analysis a diffractionist might perform "at the instrument". The material is covered in an exhaustive fashion with detailed descriptions of the various stages of the process. Practical examples of the pros and cons of different background fitting, smoothing, α₂ stripping and peak search algorithms are described which will be of use to inexperienced operators.

In chapters 5, 6 and 7 this text perhaps comes into its own in that it switches to an example-based format to cover the topics of indexing, structure solution and structure refinement. A large number of real examples, drawn from the authors' own research, and backed up with a CD of data and input files for readers to play with, are provided. The approach adopted falls somewhere between that of a classical text book and a lab manual/interactive course. Chapter 5 deals with the problems of indexing and refining unit cells. Although indexing is now largely automated the authors describe some traditional methods of manual indexing to set the scene. The use of the "classic" software packages ITO, VISSER and DICVOL is then described in depth with several practical examples. Methods for refining cells are then described, along with an outline of the least squares method. This particular section feels slightly out of place in this chapter as it's a technique that permeates much of the book, and could perhaps have been dealt with separately elsewhere, particularly as a similar treatment of non-linear least squares pops up in the middle of chapter 6. This is perhaps a chapter which will date rapidly as there has been a significant resurgence of interest in the science of indexing recently, and many new techniques/software packages are appearing to supplement the classic methods. This is, of course, no fault of the authors!

The final two chapters concentrate on methods of solving (chapter 6) and refining (chapter 7) structures. After brief introductory sections both chapters present examples from the authors' own labs. In addition to examples solved by Patterson and direct methods it's nice to see cases quoted where "crystallographic common sense" and a thorough knowledge of the literature have proved as important as using "black-box" software packages. The authors have chosen an approach in which the crystal structure of each example is solved in chapter 6 and then details of its refinement given in chapter 7. Whilst this works extremely well from the viewpoint of completeness it does lead to a slightly illogical order in chapter 7 where later examples are often less complex then earlier, and introduce no particularly significant new features. My only criticism of these two chapters is that it would have been valuable, considering the huge current interest in the area, to include a worked example in the text of the use of real space methods to solve an organic structure and illustrate the specific pitfalls that can be encountered during refinement of molecular species. It might also have been nice to illustrate (perhaps in comparison to the methods already described) the use of an alternate programme, such as the widely used EXPO.

Overall this is a useful, generally accurate and relatively comprehensive text that provides a good coverage of this area of crystallography. It is perhaps slightly long to be suitable as an introductory text for students and contains some annoying repetitions when read sequentially, but will provide a valuable reference source for any lab involved in powder work. There are areas I feel could have been usefully included, though these are clearly my personal bias. They would include non-ambient diffraction; more on topics such as the problems involved in combined neutron/x-ray refinements - how, for example, were data sets weighted in the combined refinement in chapter 7?; and more examples based on synchrotron/neutron data sets.

It's a relatively expensive text (£98 from Amazon though in the US Kluwer offer significant discounts if several copies are purchased as a course book) to expect students to buy, though this is perhaps justified for a 700+ page hard-backed book with extensive additional material on compact disk. My only caveat to potential purchasers is to think before they fly - this was the first book ever to put my travel plans in jeopardy when it tipped my Easy Jet carry-on luggage over the weight limit! Rest assured though, that the simple act of removing the book from the bag in one's right hand and carrying it through the departure lounge in one's left is sufficient to satisfy check in requirements!

John Evans