Acta Cryst. (1994). A50, 653-654
Pp. vi + 234.
Washington: US Department of Commerce, 1992
Price US $14.00. SN 003.003.03186.1
Some quiescent areas of science and technology experience a revolutionary rebirth by a sudden serendipitous discovery, as in the case of high-Tc materials, while others initiate such a renaissance through the advancement of new ideas, which may take longer to develop but whose cumulative effect results in revolutionary advances. In the field of X-ray crystallography we can point to many such milestones: the advent of direct methods for phase determination and the discovery of quasicrystals are just two instances. The advances in powder diffraction surely deserve to be ranked as another such milestone.
The first conference on Accuracy in Powder Diffraction organized in 1979 by the National Institute of Standards and Technology (NIST) (formerly the National Bureau of Standards) was a harbinger of this coming development. The sequel, the International Conference on Accuracy in Powder Diffraction II, organized by NIST for 26-29 May 1992, brought together leading experts in diverse and developing areas of the field. The proceedings provide a valuable repository for these topics and are an excellent source for crystallographers planning to initiate work in powder diffraction. Twenty-five invited papers and 73 contributions are distributed over six topics: (1) phase identification and quantification; (2) accuracy and standards; (3) new developments in software and data analysis; (4) profile fitting, decomposition and microstructural effects; (5) novel applications and structural science; (6) new developments in hardware, including detectors, and studies under nonambient and time-resolved conditions.
Crystal structure refinement from powder diffraction data has become a familiar tool to crystallographers. It requires a model with which to begin the refinement process. In the last few years, enormous progress has been made in ab initio methods for crystal structure determinations from X-ray and neutron powder diffraction data. Single-crystal crystallographers may be particularly interested in four papers illustrating various procedures of this technique, although the absence of any discussion on the use of maximum entropy is unfortunate. The use of these techniques will become very widespread and perhaps even join black-box crystallography structure determinations, when a software package incorporating the various programs becomes available. Efforts along this line are now in progress. Some very interesting modifications of the well known Rietveld technique are presented in three papers that discuss coupling the method with high-resolution transmission electron microscopy images to provide starting models; the extraction of anharmonic displacement parameters from powder data that would be especially useful in studies of high-temperature phase transitions; and the use of anomalous-dispersion effects when powder data are obtained at a synchrotron source. In addition, there are the standard topics of concern to powder diffractionists: qualitative and quantitative analyses, outlining state-of-the-art procedures for gaining more precise information by improving the data-collection modes and subsequent processing. Several papers should be of interest to materials science workers concerned with stress measurements, high-pressure investigation and glasses. These topics, however, receive less emphasis.
This volume should be of interest to a wide audience of scientists working with single crystals, powders and amorphous materials. Experts in one field of X-ray diffraction entering a new application area will find a wealth of information not only in the formal papers but also in the appended references. A subject index would have been helpful; there is an author index and a list of participants. The foreword of the volume states that the papers published in the proceedings of the first symposium in 1979 are `still widely quoted' and I believe that this volume will prove to be equally valuable.
I can't finish this review without remarking on the very touching opening tribute to Bill Parrish - given by T. C. Huang, his long-time associate at IBM - that briefly reviews his seminal contributions to the field of powder diffraction.
Department of Chemical Engineering
Materials Science and Engineering
The University of Texas at Austin
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