Charles Barrett's work in phase transformation at the atomic level helped redefine the underpinnings of the science and practice of metallurgy. His work in low temperature physical chemistry has extended its range. And, perhaps more than anyone else, as a teacher and author, he has helped introduce the technique of X-ray diffraction to the present generations of practicing metallurgists.

The relevance of his contributions is demonstrated by the continuing utility of his widely translated metallurgical text, Structure of Metals, which, when it first appeared, made the understanding of metallurgy at the atomic level accessible to a wide audience. Today this book has become a compendium of first principles.

The crystal structure of cobalt(II) acetate tetrahydrate, Co(C2H3O2)·4H2O, has been refined using single-crystal, laboratory powder, and synchrotron powder diffraction data, both individually and in various combinations. The compound crystallizes in the monoclinic space group P21/c, with a=4.80688(3), b=11.92012(7), c=8.45992(5) Å, β=94.3416(4)° at 27 °C, and Z=2. The crystal structure consists of discrete centrosymmetric trans-Co(C2H3O2)(H2O)4 complexes, linked by a three-dimensional network of hydrogen bonds. Each complex participates in 14 hydrogen bonds, 12 intermolecular, and 2 intramolecular. Compared to the single-crystal refinement, refinement of laboratory powder data yielded an average difference in bond distances of 0.02 Å, in bond angles of 3°, and in root mean square atomic displacements of 0.07 Å. The standard uncertainties of the bond distances were 0.01 Å, compared to the 0.001–0.002 Å in the single-crystal refinement. Refinement of the synchrotron powder data yielded improved accuracy and precision. It proved impossible to locate or refine hydrogen positions using a single-powder dataset, but the hydrogens could be refined using rigid groups in a joint refinement of the two powder datasets. Even from powder refinements, it is possible to obtain suitable accuracy and precision to distinguish C–O and C=O bonds, and to examine details of chemical bonding.

X-ray powder diffraction analysis of the complex of Benzo-15-Crown-5 (B-15-Crown-5) with NaClO4 displays a monoclinic crystal system with refined unit cell parameters of a = 8.829(3)Å, b = 8.327(3)Å, c = 24.21(2)Å, ß = 99.18(1)Å, V = 1757.1(1)Å3, Z = 4, and Dx = 1.48 g/cm3. The space group, P21/c, and the unit cell dimensions, determined by a single crystal diffraction analysis, agree well with those of the powder analysis. X-ray powder diffraction analysis of the complex of B-15-Crown-5 with KI displays a tetragonal crystal system with refined unit cell dimensions of a = b = 17.869(3)Å, c = 9.761(3)Å, V = 3116.7(1)Å3, Z = 4, and Dx = 1.50 g/cm3. The space group, P4/n, and the unit cell dimensions, determined by a single crystal diffraction analysis, agree well with those of die powder diffraction analysis. The powder and single crystal analyses of the two complexes indicate that in the solid phase, B-15-Crown-5 forms a 1:1 complex with Na+ and a 2:1 complex with K+. The variation in the complexation mode of B-15-Crown-5 with different cations, partially explains the lack of selectivity of this crown ether towards Na+, while from considerations of the cavity size alone this crown ether was expected to be considerably selective towards this cation.

Quantitative phase analysis of n-phase mixtures can be performed if at least n samples composed of no more than n identical phases are available. The fact that there is no need for pure phases (analytical standards) constitutes the main advantage of the method presented here. However, substitution for the pure phases by an unknown mixture of these phases decreases the diversity of the sample set and also the precision of the analysis. The crucial step in a standardless method is the creation of an initial sample set. A simple test is developed to estimate the suitability of the sample set for analysis and to evaluate the analysis error. Application of this test to 13 four-phase mixtures has confirmed its high quality.

The room temperature X-ray powder diffraction pattern of Fe2GeSe4, a II2 □ IV VI4 semiconducting compound, has been recorded and evaluated. This material was found to be orthorhombic, a=13.069(1), b=7.559(1), c=6.2037(6) Å, V=612.83(9) Å3, Z=4, Dx=5.42 gcm−3. The structure refinement carried out using the Rietveld method indicated that this material crystallizes in space group Pnma (No. 62) with an olivine type of structure. The refinement of 33 parameters led to RWP=15.3%, RP=10.2% for 5251 step intensities and RB=9.44% and RF=9.36% for 913 reflections.

Phases of general formula (RE, A)2M3O7 (RE=lanthanide, A=Ca, Sr, Ba; M=Ga, Al) are of interest for their nonlinear optical properties and have potential as solid state lasers. Their structures have been refined using X-ray and neutron diffraction data and are related to gehlenite, Ca2Al2SiO7, with M cations occupying Al and Si sites and RE and A cations sharing the Ca site with no evidence for ordering, although they occur in the ratio 1:1 because of stoichiometry; the M cations are tetrahedrally coordinated. (RE, Ba)2M3O7 compounds cannot be synthesized for M=Al or for RE cations smaller than Sm; this limitation is believed to be due to size mismatch between cations within the structure.

The X-ray powder diffraction patterns for two new synthetic calcium uranium (VI) silicate hydrate phases are reported. Ca1.5U6(OH)7O16·7H2O is orthorhombic, space group P*a*, with unit cell a=13.8949(14), b=12.0776(12), c=15.228(3) Å. The structure appears to be related to that of becquerelite. Ca2(UO2)2(Si2O5)3·10H2O was also indexed on an orthorhombic unit cell, a=12.075(3), b=15.406(6), c=26.043(6) Å. The Powder Diffraction File coverage of uranium-containing minerals which could, on the basis of their chemical formula, form in U-containing cements is also reviewed.

The following fifteen reference patterns of boride, silicide and oxide ceramics represent the first group of ceramic phases measured at the National Bureau of Standards under the project “High Quality Reference Patterns and Total Digital Powder Patterns of Technologically Important Ceramic Phases”. The support and interest of the JCPDS-ICDD in this project is gratefully acknowledged.

The general methods of producing these X-ray powder diffraction reference patterns are described in this journal, Vol. 1, No. 1, pg. 40(1986).

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 nclude the determination of phase abundance in polycrysalline 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 inerested 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.

Equations (3) and (5) should be corrected to read as follows:

Powders of Al and Ti were blended and compacted, the compact then melted in an attempt to produce single phase Al3Ti. Optical microscopy of the cast and homogenized specimen revealed an almost single phase microstructure with minor amounts of a second phase. The composition of the matrix was measured using fully quantitative energy dispersive X-ray analysis. By use of X-ray diffractometry, the interplanar spacings and the associated integrated peak intensities were experimentally measured for the binary DO22 compound, Al3Ti. Using standard structure factor equations, the intensities were calculated for the various reflections. Good agreement was obtained between calculated and observed intensities.

After regeneration, the catalyst UOP-R-62 was used for conversion of reforming benzine. The percentage of conversion benzine fraction was considerably smaller than that of the new catalyst sample. To determine the cause of catalyst deactivation, in addition to standard methods of analysis, X-ray diffraction and scanning electron microscopy were used. Real and model samples of UOP-R-62 were analysed. Real samples were prepared with the new catalyst, a used and regenerated catalyst with good activity and a deactivated catalyst. Model samples were prepared from the new catalyst by heating at 400–1100 °C in a porcelain crucible in a muffle furnace for 1 h. Prepared samples were measured in a Philips diffractometer system and examined in a scanning electron microscope. The obtained diffractometer patterns, FWHM value of the 440 reflection of γAl2O3, electron micrographs and images of emitted characteristic X-rays were mutually compared. Only the values obtained from the deactivated catalyst differed from the others. Besides reduced broadening of the 440 line the material exhibited new X-ray diffraction lines, a change in phase composition, and modifications in morphology and microstructure. These changes are an indication that overheating of individual spheres of catalyst UOP-R-62 to a temperature of 700—1100 °C or higher caused their deactivation.

Indexed X-ray powder diffraction data derived from Rietveld crystal structure refinements are reported for synthetic potassium-richterite (KRC: K[CaNa]Mg5Si8O22(OH)2), nickel-potassium-richterite (NIKRC:K[CaNa] Ni5Si8O22(OH2) and cobalt-potassium-richterite (COKRC:K[CaNa]Co5Si8O22 (OH2). The following dimensions were obtained: KRC: a = 10.0547(8), b = 17.997(1), c = 5.2746(4)Å, β = 104.832(5)°; NIKRC: a = 10.0297(7), b = 17.942(1), c = 5.2576(4)Å, β = 104.982(5)°; COKRC: a = 10.1166(9), b = 18.066(1), c = 5.2752 (4)Å, β= 104.846(6)°.