A standard test method for the determination of RIR values by x-ray diffraction
Walter N. Schreiner
IC Laboratories, P.O. Box 721, Amawalk, New York 10501
(Received 22 November 1993; accepted for publication 24 June 1994)
The measurement of x-ray diffraction line intensities is the basis for quantitative phase analysis (see
for example, Chung (1974), Davis (1986), and Hubbard and Snyder (1988)). While there are many
sources of error in such measurements, in recent years computer automation of powder
diffractometers and associated analytical software has made such measurements more practical and
accurate. For example, profile fitting software has made it possible to determine integrated peak
areas and to deconvolute overlapping lines. Another problem which affects quantitative analysis is
the systematic error in instrument sensitivity as a function of 20 diffraction angle. This effect has
been partially responsible for poor reproducibility of relative intensities between laboratories
(Schreiner and Kimmel (1987), and Jenkins and Schreiner (1989)). But, because the error is
systematic, corrections may be made by using a standard such as the National Institute of Standards
and Technology SRM 1976 alumina plate (NIST 1991). These and other advances have led to a
renewed interest in the determination of I/Ic (also called RIR - Reference Intensity Ratio) values for
crystalline substances (e.g., Snyder (1992)). I/Ic is defined as the ratio of the intensity of the
strongest line of an analyte to the corundum (113) line when the analyte is mixed 50:50 by weight
with corundum. We present here a standard procedure used in our laboratory to experimentally
measure I/Ic values, and which explicitly incorporates profile fitting and instrument sensitivity
corrections. The procedure is written in the format of an ASTM (American Society for Testing and
Materials) standard test method, however, inter-laboratory round robin tests have not been carried
out to determine precision and bias associated with the method. While the method calls for
corundum as the internal standard, another standard material, s, may be used, in which case the
procedure will result in a ratio I/Is. Hubbard and Snyder (1988) have shown how to convert between
I/Is and I/Ic. This method is based on the procedure routinely published in NBS Monograph 25 until
1986. It is augmented with corrections for the angularly dependent instrument sensitivity and with
calculations of I/Ic for both variable and fixed divergence slit configurations. A Quattro Pro
spreadsheet is used in our laboratory to do the calculations. An example of the spreadsheet is given
in the appendix for one of two I/Ic runs of MgCO3. We also utilize the corundum in the I/Ic runs as
an internal standard to determine displacement error corrections for preparation of digitized patterns
of pure analyte phases. These patterns are submitted to the International Centre for Diffraction Data
for inclusion in a whole pattern data file planned for some time in the future. The notation used here
is the standard notation developed for the RIR method by Hubbard and Snyder (1988) and
systematically extended by Snyder (1992). A table of the notation is given in the Terminology
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