Powder X-ray diffraction data for cubic La0.3Sr0.7CoO3−δ, perovskite prepared by a combustion method, using metal-EDTA complexes are reported. The cubic cell parameter is: ac = 3.8323(9)Å.

Limitations in powder diffractometry imposed by scatter slits and/or a diffracted-beam monochromator, which have been ignored in the past, are discussed and mapped quantitatively. These limitations become manifest especially with ωoffsets, i.e.in stress measurements and with ωoscillation to improve the reproducibility of intensities in the presence of too coarse grains. The limitations can only be established with knowledge of slit sizes and with precise alignment of all slits, their holders and the diffracted-beam monochromator. To that end, concise, accurate procedures for obtaining these measurements in-situare proposed.

The Powder Diffraction File (PDF) is a collection of single phase X-ray powder patterns, maintained and distributed by the JCPDS-International Centre for Diffraction Data. Over the past 10 years there has been increasing use of the PDF in computer readable form, but the limited amount of disk space available on most commercial powder diffractometer systems has limited use to a small subset of the total PDF. The recent availability of low-cost Compact Disk Read Only Memory (CD-ROM) systems offers an attractive alternative to conventional disk media. This paper describes a low-cost Personal Computer/CD-ROM system, “PC-PDF”, having a total available storage of 550 Mbytes. While seek times are relatively slow – typically, 0.5 seconds are required to traverse the complete PDF – by use of optimum packing and access algorithms, search strategies based on PDF numbers, chemistry, strongest d-spacing, etc., operate at a speed causing no great inconvenience to the user.

Detailed procedures for solving small crystal structures ab initio with the maximum-entropy (ME) methods using X-ray powder diffraction data are described by determining the structure of the low-pressure phase of magnesium boron nitride, Mg3BN3(L), which was previously solved by one of the authors and co-workers using the Patterson method and the direct methods. The simple ME method devised by Gull, Livesey, and Sivia failed to correctly phase the structure-factor data, leading to noninterpretable electron-density maps. This method, maximizing the entropy under the constraints of the observed structure factors with subsequent incorporation of strong extrapolates in the basis set, trapped the solution in a local entropy maximum, from which there is no way to move. The multisolution method of phase determination by entropy maximization and likelihood evaluation, developed by Bricogne and Gilmore, successfully located all the Mg, B, and N atoms in one cycle of phase extension. The correct solution had a highest log-likelihood gain, but a minimum entropy, among the multisolutions generated by phase permutation.

X-ray powder diffraction data for the spinels CoAl2O4 and CoGa2O4 were measured with synchrotron radiation using λ = 1.2033 Å, determined with Si as a standard (a = 5.4305 Å). The two blue compounds prepared hydrothermally are cubic with space group Fd3m. Profile refinements gave the results: CoAl2O4 had a = 8.0968(1) Å and composition (Co0.71Al0.29]Al1.71Co0.29]O4 and CoGa2O4 had a = 8.3229(1) Å and composition Ga[CoGa]O4. The degree of inversion is thus 0.29 for CoAl2O4 and one for CoGa2O4.

Powder X-ray diffraction data are reported for La0.6Sr0.4Co1−yFeyO3 (y=0.1, 0.25, 0.4, 0.6, 0.8, 1.0). The powders were prepared by thermal decomposition of metal-containing complex solutions. All compositions have rhombohedral unit cells. In hexagonal setting, the cell parameters are a=5.4388 Å, c=13.2355 Å for y=0.1; a=5.4427 Å, c=13.2542 Å for y=0.25; a=5.4530 Å, c=13.2838 Å for y=0.4; a=5.4769 Å, c=13.3175 Å for y=0.6; a=5.5057 Å, c=13.3918 Å for y=0.8; and a=5.5278 Å, c=13.4368 Å for y=1.0. The space group is probably R3c (167) for all compositions. The observed trends in the change of the pseudocubic cell parameter ac with increasing iron content can be explained in terms of substitution of Co4+ by Fe4+ when y<0.4, and substitution of Co3+ by Fe3+ when y≳0.4.

An indexed powder diffraction pattern and related crystallographic data are reported for secnidazole [C7H11N3O3, IUPAC name: 1-(2-hydroxypropyl)-2-methyl-5-nitroimidazole], which is not represented in the Powder Diffraction File. The unit cell dimensions were determined from diffractometer methods, using monochromatic CuKα1 radiation, and evaluated by indexing programs. The monoclinic cell found for 1-(2-hydroxypropyl)-2-methyl-5-nitroimidazole is: a=12.426(2) Å, b=12.173(2) Å, c=6.656(1) Å, β=100.19(1)°, Z=4, space group P21/c (No. 14), Dx=1.271 g/cm3. Crystallization of an anhydrous powdered sample of secnidazole in a buffer solution of Na2B4O7 and NaOH (pH 10.4) resulted in crystals that contained water of crystallization, as shown by single crystal structure determination. Secnidazole exhibits crystal pseudopolymorphism, because the experimental powder pattern of the anhydrous form and the calculated pattern from the structure determination of the hydrate form are similar. Observed powder diffraction data for this drug were interpreted with the aid of a calculated pattern based upon the crystal structure determined. The cell found by TREOR90P for anhydrous secnidazole is in good agreement with that of the hemihydrate form determined from single crystal diffraction: a=12.424(2) Å, b=12.187(2) Å, c=6.662(1) Å, β=100.9(1)°; Z=4.

A new, convenient program has been designed and implemented on a VAX computer to facilitate the use of the Johnson/Vand program (Version 21) for identifying components in crystalline mixtures by X-ray diffraction. (The data base of references is distributed solely by the JCPDS – International Centre for Diffraction Data.) This new program uses an easy-to-follow conversational mode of communication for setting up the input file for the identification program from a remote terminal. The program is menu driven with screens for input of sample information, for change of default computational parameters, and for handling the experimental diffraction data. Many of the input screens can be readily bypassed when the default parameters are acceptable. An editor feature is provided for viewing the final input file and for correcting the diffraction data.

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.

Precise X-ray powder diffraction patterns of two isostructural triborates, CsB3O5(CBO) and TlB3O5(TBO), have been collected on a D5000 diffractometer with a primary monochromated beam (λ CuKα1=1.5406 Å). Refinement of indexed reflections in the space group P212121 led to: a=6.201(1) Å, b=8.514(2) Å, c=9.176(2) Å, Z=4, Dx=3.363 for CBO and a=5.2156(4) Å, b=8.2659(6) Å, c=10.2240(9) Å, Z=4, Dx=4.773 for TBO. The Smith–Snyder figures of merit are F30=53.0 (0.0101, 56) for CBO and F30=112.9 (0.0074, 36) for TBO. These values are much better than the previous ones published in Powder Diffraction File.

Two compounds of the elpasolite family (A2BLnX6), Cs2KTbCl6 and Cs2KEuCl6, were obtained {by evaporating to dryness a hot aqueous HCl solution of the appropriate chlorides [Morss etal., Inorg. Chem. 9, 1771 (1970)]} and characterized by powder X-ray diffraction. Title compounds are isostructural with cubic Rb2NaTmCl6 and correspond to the perovskite related structure with space group Fm3m, cell parameters 11.1294(6) and 11.1618(4) Å, V=1378.5(2), and V=1390.5(1) Å3, respectively.