An Fe-containing deposit isolated from a commercial plant was identified by indexing its powder diffraction pattern, using the NIST Crystal Data Identification File to locate an isostructural Mn compound, and carrying out a successful Rietveld refinement. The principal phase in the deposit was confirmed to be bis(ethylammonium) tetrachloroiron(II). This compound crystallizes in the orthorhombic space group Pbca, with a=7.3291(6), b=7.2603(6), c=21.7544(8) Å, V=1157.59(14) Å, and Z=4. The structure consists of single perovskitelike layers of corner-sharing FeCl6 octahedra parallel to the ab plane, separated by bilayers of ethylammonium cations. The octahedra are tilted 4.4° with respect to the c-axis, and the layers are ruffled. The compound was apparently formed by reaction of the ethylamine corrosion inhibitor with Fe from the steel process vessel and chloride in the process stream.

The effect of crystallite-size distribution on the shape of X-ray diffraction peaks from powder samples is investigated focusing the attention on the region within the top half of intensity. It is shown that, unlike profile tails, this central region can markedly depart from the Lorentzian shape for crystallite-size distributions that are quite acceptable from the physical point of view. Goal of this paper is to correlate the well-known m parameter in the Pearson VII function or the η weight in the pseudo-Voigt function with a number of different distributions of crystallite dimensions ranging from the δ function of all-equal-sized crystals to a very broad distribution. The suitably normalized curvature at the peak is a possible new parameter; its correlation with m and η is shown. Also, a procedure is suggested to derive the volume-average crystal thickness 〈Tw〉 from the FWHM and the knowledge of either m or η.

A model for the crystalline structure of Ba2YCu0.25W0.75O6 solid solution is given. The model proposed a perovskite ordered structure, with a cubic unit cell made from eight perovskite-like units and having a symmetry described by the space group Fm3m. The crystalline structure was refined by the Rietveld technique, giving RF=0.048 for 82 reflections. The solid solution was characterized by the following parameters: Z=4, Mr=613.2, a=8.43630(8) Å, V=600.42(1) Å3, Dx=6.78 g cm−3, μ=209.04 mm−1, and F(000)=1047. The model assumed that copper and tungsten atoms, which were ordered with Y atoms, had the same local environment. Therefore, it was only a first approximation to the crystalline structure.

The new phase LaCr(NO3)6·12H2O was synthesized from a nitric acid solution. The symmetry is trigonal with the parameters a=10.9564(4) Å and c=16.835(1) Å [V=1750.2(2) Å3, space group R-3]. The thermal decomposition, studied by temperature-dependent X-ray powder diffraction and thermogravimetry, gave successively the cubic phase LaCr(NO3)6·6H2O [a=12.301(1) Å, space group P213] and the chromate(V) LaCrO4. The reduction of LaCrO4 to LaCrO3 occurred at a temperature depending on the oxygen pressure in the reaction atmosphere.

A quantitative simultaneous determination method by X-ray powder diffractometry is described for calcium sulfate and calcium carbonate in airborne dusts. In order to eliminate the mutual interference among diffraction peaks, and to avoid the presence of the hydration isomers of calcium sulfate, dust samples were heated at 350°C for 2 h. To reduce the errors due to the difference-in crystallinity between the standard materials and the samples, the synthesized calcium sulfate anhydrate (anhydrite) was heated to such an extent that the half-width of the 002,020 peak was identical with that of the anhydrite in pretreated dust samples. Standard calcium carbonate (calcite) was ground until the half-width and the orientation index of the 104 peak of calcite was identical with that of the calcite in dust samples. Linear calibration curves were obtained throughout the range of 0 ∼ 30 wt% for anhydrite and the range of 0 ∼ 10 wt% for calcite, respectively. The determination limits were 0.2 wt% for anhydrite and 0.3 wt% for calcite. Relative standard deviations were 3.4 % for 8.0 wt% of anhydrite and 1.8% for 5.4 wt% of calcite. The present method is applicable to determination of calcium sulfate and calcium carbonate in actual dust samples.

Fourteen reference patterns of oxide ceramics are reported. Included in the fourteen reference patterns are data for nine high critical temperature super-conducting oxide related phases: (BaCuEr2O5, Ba2Cu3EuO7, BaCuGd2O5, Ba2Cu3GdO7, Ba2.4Cu5La4O13, Ba1.9cu3La1.1O7, Ba2Cu3SmO7 and (Ba0.4Sr0.6)2Cu3 YO7). The general methods of producing these X-ray powder diffraction reference patterns were described previously in this journal (Vol. 1, No. 1, pg. 40 (1986)). The symbols used in this article are defined in the PDF cards.

A previously manually operated film comparator used to evaluate Guinier films has been automated as a film scanner of the flat film type. The film movement is controlled by a stepper motor and the intensity of the transmitted light is recorded as a function of position on the film. A personal computer controls the stepper motor and records the measurements of the transmitted light intensity. The data quality is judged from refinements of lattice constants for α-SiO2 and ZrO2. The powder pattern for Pb2Sr2Ho0.625Ca0.375Cu3O8 and a high temperature study of the thermal expansion of GeO2 are presented.

An external standard method using mica for angular calibration of powder diffractometers is described. This is useful especially when standard referee materials certified by the US National Institute of Standards and Technology are not accessible.

The complexes [C(NH2)3]3MF6, M = Cr, Fe have been isolated from aqueous solutions of the corresponding fluorides. The compounds are isostructural and crystallize in the cubic space group with a = 14.0667 (6) Å for M = Cr, a = 14.1246(8) Å for M = Fe and Z = 8. The MF63− anions are arranged as Na+ and Cl− in the NaCl lattice. Guanidinium cations are distributed on 24-fold general position.

The effects of sample transparency in a powder diffraction experiment are discussed, and formulas including effects from horizontal divergence are derived. It is shown that the classical formula by Alexander [L. E. Alexander J. Appl. Phys. 21, 126 (1950)] is only a limiting case for zero horizontal divergence. It is also shown that in some cases extinction effects can play a role. The impact of these effects on both the line profile as well as the integrated intensity and experiments illustrating these phenomena, are discussed.

Powder diffraction patterns have been calculated for nine isostructural rhombohedral M2(SO4)3 (M = Sc, Ti, V, Cr, Fe, Ga, Y, Rh, In) phases, and for four isostructural monoclinic M2(SO4)3 (M = V, Fe, In, Tl) phases. The pattern for monoclinic Fe2(SO4)3 is the first reported for this phase. Because structure data are available only for the two Fe2(SO4)3 polymorphs, the powder patterns of the other trivalent metal sulfates were approximated using the structure data of the isostructural Fe phases with the scattering factors and previously determined cell parameters of the various metal sulfates. These calculated patterns are termed an approximation by isostruduralism.

The calculated patterns were used to evaluate reference powder data for these phases in the Powder Diffraction File (PDF). All but two of the PDF patterns were found to differ substantially from the calculated patterns in the stronger peaks used for identification, and to be missing weak peaks that may be confused for impurities during phase identification.

A new diffraction pattern of the high-temperature and high-pressure polymorph Mg3(PO4)2-III (PDF 43-500) is given and indexed on the basis of a single-crystal structure refinement. It allows diffractogram indexing of the isostructural high-temperature and high-pressure form of Co3(PO4)2 (PDF 43-499).