F.H. Chung & D.K. Smith, "Industrial
`
`Applications of X-Ray Diffraction", Dekker,
`
`(2000), p21
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`RS 1025 - 000001
`
`

`
`Frank H. Chung
`Sherwin-Williams Company
`Chicago, Illinois
`
`Deane K. Smith
`The Pennsylvania State
`University
`University Park, Pennsylvania
`
`MARCEL DEKKER, INC.
`
`RS 1025 - 000002
`
`

`
`., . _ .._,__.........-........----m.-....-.4
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`RS 1025 - 000003
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`

`
`The Pm'c!iee of Dtflractfon Ana1y.ri.v
`
`2}
`
`may be used: individual peak information, the complete set ofd and 1 information, and
`as the whole trace. Individual peak information and the d—I set may be obtained from
`the trace by utilizing various peak-finding algorithms or by peak profile fitting using
`programs such as PRO—FlT (Toraya, 1986, 1993) and SHADOW (Howard and Preston,
`1989). The full pattern may be analyzed for only the peak positions by programs such
`as WPPF, which fits the unit cell parameters for one or more phases to the trace.
`Programs such as that of LeBail, Duroy, and Fourquet
`(1988) may accomplish the
`extraction of‘ the intensities for structure analysis. The Full structure refinement may
`be carried out by many Rietveld programs (Young, 1993). It is also possible to graphically
`decompose patterns by superposing a reference pattern from a full-pattern database
`without processing the raw data in any way (Smith, Hoyle, and Johnson 1993).
`It should be mentioned that there are two ways to extract information from a diffraction
`peak: decomposition and deconvolution. These terms are commonly misused, especially
`deconvolution. Decomposition is the separation of overlapped peaks by using a selected
`analytical profile and optimizing the fit ofthe cluster by adjusting the profile parameters.
`Deconvolution is the extraction of the sample contribution in a profile from the source
`and instrument contribution by elaborate mathematical methods that may involve some
`approximations. The profile—fitting procedures used for extracting position and intensity
`information involve decomposition. Separation ofsize and strain information by procedures
`such as the Warren—Averbach method involves deconvolution
`
`5. ANALYTICAL METHODS
`
`Powder diffraction techniques may be classified into those that yield a qualitative answer and
`those that yield a quantitative answer. Qualitative answers include confirmation or identi-
`fication of the phases present in a specimen and crude estimates of how much is present.
`Quantitative analysis provides numbers with estimated accuracy for crystallographic par-
`ameters including lattice dimensions, phase abundances, crystal structure coordinates,
`and other physical property data.
`The data in the PDF are most commonly used for phase identification. It must be
`remembered, when using the PDF, that all the d—1 tables are based on peak information.
`That is, the ds and P3 are reported for the peak positions from the experimental trace,
`and the peaks in a cluster are not decomposed into individual components. When making
`comparisons of diffraction data with the PDE one must use peak heights versus peak
`heights not peak areas versus peak heights {i.e., apples versus apples, not apples versus
`oranges).
`
`5.1. Qualitative Phase Analysis
`
`The identification of‘ phases based on their powder diffraction pattern dates back primarily
`to I-lanawalt and Rinn (1936) and became a common procedure when the Powder
`Diffraction File was published and contained sufficient data sets to yield matches. As
`the coverage of the PDF improves, phase identification also improves,
`It is impossible
`to locate a match for an experimental data set if the data for the phase in question are
`not included in the reference file.
`
`Where the user only wants to confirm the presence of a phase in a sample, it is a simple
`matter to locate an appropriate reference powder diffraction pattern and collect
`the
`experimental data for comparison. The problem arises when the user has little or no in-
`formation from which to start. Fortunately, the powder diffraction pattern can be a sufficient
`
`RS 1025 - 000004