Advances in X-Ray Analysis

Deane K. Smith Department of Geosciences The Pennsylvania State University Computer automation of x-ray powder diffraction has been one of the dominant topics of this conference for many years. In fact, the first description of such instrumentation dates back to 1967, Rex (1). The modern instruments are considerably more sophisticated than this early unit, but the goals of automation are essentially unchanged. They are to obtain better data at a faster rate with less effort than is possible with manual instrumentation. Indeed laziness is the mother of invention. The emphasis of most of the papers on automation has been tm-lard hardware-controlling systems and aC,lieving accurate d values and good intensities for effective phase identification and phase characterization. Tests of good data include successful pattern searching and matching. Indexing by computer methods or accurate lattice parameters through least-squares fitting procedures with resulting small residuals is a good test of d value accuracy. Intensity accuracy is much harder to test unless a theoretical data set is available. In most of the reported studies, the emphasis has been more on the data acquisition than on the specific problems to which the data is to be applied. In organizing this plenary session, an attempt was made to focus on applications, especially those which are at the forefront of materials studies. In addition many other applications papers were encouraged with the result that a good variety of such topics are included in the program this year.