The resemblance between powder patterns because of similarity of crystal structures is well known and widely used. This phenomenon facilitates the determination of unit cells and is frequently used to predict crystal structures of new substances. At present the matching of diffraction analogues is done mainly by hand. Some approaches have been considered in this paper for applying a computer to the problem. Four numerical criteria for resemblance of powder patterns are suggested. Powder patterns are matched with patterns in a database by making use of a computer program based on these criteria.

The procedure results in a short list of powder patterns to be examined by the expert. The efficiency of the program is illustrated by examples of calculations for substances of both high and low symmetry. The search system may find an important application in X-ray powder diffraction analysis for the identification of solid solutions, of substances documented under unusual conditions, of structure analogues and for classification of patterns in a database.

Two new VAX/VMS computer programs are presented for accessing and searching the Powder Diffraction File (PDF) (1989) of the JCPDS-International Centre for Diffraction Data (ICDD). The programs use binary mapped index files which affords rapid searches of the database. Program LOGIC permits entries in the database to be selected by chemistry, peak position or name constraints. The selected entries may be displayed, printed or graphed. The program can display or print entries from the full PDF-2 (1989) database, if on-line. Program SEARCH searches for patterns in the database which match an unknown set of peaks; the program may be optimized for a wide variety of applications including identification of component phases in mixtures. Commands may be entered to the programs in two modes. In the “novice-friendly” mode, users must answer questions to select options. However, experienced users may opt to use a concise one-line command syntax. The modes may be mixed.

The relative intensities ratios for the determination of the relative amounts of alpha and beta phases in silicon nitride and the relative amounts of delta yttrium disilicate (Y2Si2O7) and nitrogen apatite [Y5(SiO4)3N] are reported. These constants were determined using an iterative method applicable when the pure phases are not easily prepared. In addition, a calibration curve was obtained for the quantitative measurement of free silicon in silicon nitride over the range 0 to 0.3% by weight of Si.

The usefulness of an X-ray powder diffraction data base, such as the one published by the International Centre for Diffraction Data, is largely dependent on continued additions of indexed powder patterns of single-phase materials of interest to data-base users. The single-phase character of a specimen is generally established by using known values of the unit cell constants to index all its powder pattern lines.

In this manuscript we describe indexing procedures based on crystal data which provide only relative values of the cell dimensions, rather than the absolute values usually considered to be essential to the indexing process. To the best of our knowledge, the use of such data for indexing powder diffraction patterns has generally been overlooked or ignored by X-ray crystallographers. We refer to the large numbers of goniometric measurements of crystals which have been published both before, and since, the discovery of X-ray diffraction. These provide useful descriptions of chemical and physical properties of crystals as well as measurements of relative dimensions of unit cell axes. The latter are presented in the form of a/b, b/b and c/b, together with the interaxial angle or angles, if the cell is nonorthogonal.

This paper contains a review and explanation of the super conducting Ruddlesden-Popper phases in the systems Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O. Calculated powder X-ray patterns for the phases Bi-2201, 2212, 2223, and 2234 (where the numbers refer to the stoichiometric ratios of Bi:Sr:Ca:Cu) and Tl-1201, 1212, 1223, 1234, 2201, 2212, 2223, and 2234 (here the numbers refer to the molar ratios of Bi:Ba:Ca:Cu) generated from the reviewed crystal structures are presented. Observed powder patterns for Tl-2201, Tl-2212, Bi-2201 and Bi-2212 are included and compared to the calculated patterns of these phases.

Yttrium aluminium garnet, Y3A15O12– YAG, has a powder diffraction pattern that is easy to analyse in principle, but shows very interesting problems. These problems are revealed using an interactive graphics system, UNIRAS, intregated with some of the usual procedures for crystallographic data processing. For example, indexing with the APPLEMAN procedure is improved when the high-angle peaks are properly identified, and the cell parameters then refine to a high precision. Iterations between refinements and graphical analysis allows the operator to identify even some of the very weak peaks in the pattern. Using the peak positions from the refinement, the experimental data can be analyzed for instrumental aberrations and corrections can be applied to improve the accuracy of the cell parameter.

Ba2NaNb5,O15 and eighteen additional compositions in the NaNbO3-BaNb2O6 system from 60 to 85 mole % BaNb2O6 have been prepared and studied by X-ray powder diffraction. A calculated pattern has been used to aid in indexing the powder pattern of stoichiometric Ba2NaNb5O15(BNN-S). The lattice parameters of BNN-S have been determined from repeated measurements of 2 higher order reflections and are a=b=17.5994(8)Å and c=7.9771(9)Å. A comparison with the Powder Diffraction File (PDF) 34-210 indicates that the present data provide a more precise match to the unit cell, include additional weak reflections and cover a greater 2θ range. There is a tungsten bronzetype solid solution range from 60 to 75 mole % BaNb2O6.

Quantisation of low-quartz in crystalline mixtures has been performed by X-ray powder diffractometry (XRPD) for many years. Conventional methodology, using discrete-peak integrated intensities, is frequently performed employing calibrations prepared with natural low-quartz specimens. Previous research showed that from a conventional XRPD study of low-quartz specimens, the amorphous content of a suite of natural low-quartz specimens ranged from 1% to 28%. That study thereby underlined the importance in XRPD calibration of characterising the amorphous content (or its complementary quantity “weight fraction of crystalline material, WCFM” employed here). This paper describes an application of pattern-fitting Rietveld analysis for characterising the WCFM in a suite of low-quartz specimens. The results gave WCFM values ranging from 0.91 (esd, σ= 0.02) to 1.00(0.02) for six specimens for which the SiO2chemical content ≥ 99.5%.

Don Hanawalt died three years ago this June. To those of us who were privileged to know him he was a special person, a man of boundless energy and tireless enthusiasm. In a very real sense Don was a founder in the use of the powder diffraction as a practical laboratory technique. His pioneering contributions included the universally employed search method which, today, still bears his name, and which really established qualitative phase identification. To Don's chagrin, his work never received the same enthusiastic acceptance among chemists that it did by mineralogists and metallurgists. Several months before Don died, Richard Rose of the Journal Staff interviewed Don with the idea of writing an article for the Journal covering Don's contributions to the field of powder diffraction in general, and his work within the International Centre in particular. Because of Don's untimely demise the work was never completed… but in order that a description of Don's interest and work in the powder diffraction field should be recorded, we have taken the tape transcripts and edited them into what we hope will be a cohesive, if somewhat abbreviated, story. Where possible, we have retained the actual language of the interview. Where necessary, minor corrections have been made to some of the dates mentioned by Don. The interview starts by reviewing the early days of X-ray analysis.

That very large famous and infamous borough of New York City, namesake of one of the country's most graceful bridges, Brooklyn, was perhaps the least likely of places for the development of a teaching center of international brilliance – and, at that, in the then little known field of X-ray diffraction. Such was the case, however. Where else, it has been asked, could a visiting lecturer on X-ray technique look out at his audience and, to his dismay, find in the front row, Paul P. Ewald, Herman Mark, Isidor Fankuchen and David Harker – respectively, a founding father of X-ray diffraction, a founding father of polymer chemistry, an entrepreneur par excellence in X-ray crystallography, and a major player in macromolecular (proteins) analysis. Only there at the Brooklyn Polytechnic Institute. It was unique in its time and function as the pre-eminent school of learning for the rapidly evolving practices of polymer science and X-ray diffraction.

The paper describes a stepping motor unit which can replace the mechanical connection between a goniometric circle (ϑ or 2ϑ) and the rotatory movement of the Automatic Divergence Slit attachment.

The superconductor related phases Ba3R3Cu6O14+x(or Ba2−zR1+zCu3O7+x, with z=0.5), where R = Pr, Nd, Sm, and Eu, have been prepared and characterized by X-ray powder diffraction, ac magnetic susceptibility measurement, resistivity measurement and thermogravimetric analysis (TGA). Attempts to make corresponding compounds with R = Gd, Dy, Y, Er, and Lu were not successful; they do not appear to form for rare-earth elements, R, with an ionic size smaller than Eu. The oxygen content of the successful materials was estimated by TGA. The Ba3R3Cu6Cu14+xcompounds which were sintered at 950°C and annealed in oxygen at 550°C were found to be nonsuperconducting above 10K. Previously reported results for the R=La compound have indicated that it was superconducting with a transition temperature of 15K The oxidation-reduction behavior of the Ba3R3Cu6O14+xmaterials is similar to that of the superconductor phases Ba2RCu3O6+x.

These present isostructural compounds are tetragonal with a space group of P4/mmm. The cell parameters range from a = 3.8612(4), c = 11.5624(14) Å, V = 172.38(4) Å3in the Eu compound to a = 3.8893(3), c = 11.6370(11) Å, and V = 176.03(3) Å3in the Pr compound. The standard X-ray diffraction patterns of these materials are given.

The crystal structure of metastable Li2Si2O5, Fw = 150.05, has been refined by the Rietveld method using high resolution X-ray powder diffraction data recorded at the Daresbury Synchrotron Radiation Source on the new 8.3 diffractometer. Li2Si2O5, in keeping with many compounds of interest to the materials scientist, exhibits relatively broad diffraction peaks. It is important to establish the quality of crystal structure data that may be obtained from such materials on this new instrument. Various functions were used to model the peak shape from this instrument; a split-Pearson VII function appeared to be marginally superior to Pearson VII or Pseudo-Voigt functions. Refinement was carried out using the split-Pearson VII in the space group Pbcn (60) and terminated with a = 5.6871(6), b = 4.7846(5), c = 14.645(1) Å, V = 398.50 Å3, Z=4, Dc= 2.502 gcm−3, Rwp = 17.06, Rex = 14.48 and Χ2 = 1.39. The refined parameters are compared with those obtained from a previous single crystal X-ray determination.

Recent developments in the Rietveld method for the analysis of powder diffraction data have seen the method evolve from its original purpose of crystal structure refinement to include the determination of phase abundance in polycrystalline mixtures and the estimation of crystal size and strain parameters. However, the Rietveld method is not easy to use and may deter many powder diffractionists, who are not interested in structure refinement per se, from using the method in its non-structural applications.

In order to overcome the difficulties in using the Rietveld method, a program, QPDA (for Quantitative Powder Diffraction Analysis), has been written that sets the conditions necessary for a single or multi-phase refinement, runs the Rietveld program and extracts phase abundance and size/strain information from the refined parameters. The program comprises a user-friendly, default-driven system of subroutines, written initially in VAX Fortran, and operates from a database of inorganic materials frequently encountered in a wide range of minerals and materials science industries.

Two methods may be used to measure the reference intensity ratio: (1) by measuring intensities from samples prepared by mixing the analyte and standard together in a known weight ratio and (2) measuring separately the intensities for the analyte peak and reference standard peak from pure phase preparations and by correcting the intensities with mass absorption coefficients. Both methods give identical results that are independent of the difference in mass absorption between analyte and standard. These reference intensity ratios may be universally applied to both matrix flushing and adiabatic procedures in multicomponent analysis providing that preferred orientation, microabsorption, and extinction can be eliminated or greatly minimized in the samples under analysis.

A method of analysis for X-ray diffractometry is proposed for determining the number and the concentrations of phases in a series of samples of the same multiphase system. This method can be used when n samples containing N phases, where N<n, with different concentrations are given or prepared from a given sample.

The method of principal component analysis was applied to the determination of the number of individual phases in multiphase mixtures. A quantification method using the intensity ratio to an arbitrary chosen standard mixture, which is also one of the mixtures to be analyzed, is proposed.

In this study, we examined the validity of this method for X-ray diffractograms of two and three component systems. It is shown that the values determined by the present method are in good agreement with the prepared concentrations of the samples.

A program has been written for rapid lattice parameter refinement which is designed to be applied to components in a mixture. This FORTRAN program employs a linear least-squares technique and is applicable to crystal systems with symmetry orthorhombic or higher. In addition to lattice parameters, a 2θ-zero can also be refined. Either approximate lattice parameters or a minimal set of indexed lines can be used as input. An example is given of its application to a AuMn two phase system.

A study has been conducted with gibbsite specimens, on the use of Rietveld X-ray powder diffraction (XRPD) pattern fitting for quantitating preferred orientation in powders. This study has shown that an earlier formula gives results which correlate closely with an empirical measure of morphology proposed recently for gibbsite powders, viz., the ratio of the XRPD intensities for the (002) line and the (110, 200) doublet lines. A method is proposed on the basis of this correlation for the correction for preferred orientation of line intensities in gibbsite powder patterns. The correction method appears to have excellent potential for XRPD quantification of gibbsite levels in mixtures, and could have general application for coping with preferred orientation effects in the quantitation of other phases.

The texture index introduced by Harris (1952) is reconsidered from the point of view of the orientation distribution of crystallites in a flat powder specimen. It is shown that the texture index can be used as an approximate measure of texture degree or as a texture correction factor in cases of a weak texture. Its failure in both these aspects for the strong textures is caused by an incorrect averaging of pole densities contained in the original definition of this quantity.

The structures of orthorhombic (a=5.5686(2)Å, b=9.8946 (2)Å, c=3.19369(12Å) and cubic (a=9.177(3)Å) Cd2SnO4were refined by Rietveld analysis of X-ray powder diffraction patterns. Both of these polymorphs were chemically treated with hydrogen gas mixtures at 400°C, resulting in a colour change from yellow to green. Small structural changes were observed for the orthorhombic material, which underwent a uniform contraction (≈0.02%) of cell size and movement of some oxygen atoms towards the tin atoms. Evidence for loss of structural oxygen was sought, but could not be found above the detection limit of 0.3%. Cubic Cd2SnO4possesses the spinel structure with a large (at least 65%) degree of inversion. Samples prepared with a smaller cell have so far proved unsuitable for Reitveld analysis.