New hexafluoroniobates IV, VNbF6 and the high-temperature form of CrNbF6 have been synthesized by solid-state reaction. The former is isostructural with rhombohedral LiSbF6, space group R3¯, and the latter crystallizes with tetragonal symmetry, space group I/4mmm. Unit-cell parameters were determined: a=5.520(1) Å, c=13.987(5) Å, V=369.0(1) Å3, Z=3 for VNbF6, and a=5.5403(5) Å, c=8.453(1) Å, V=259.5(1) Å3, Z=2 for the “HT” form of CrNbF6. Powder diffraction data are reported.

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.

Cristobalite and tridymite are distinct forms of crystalline silica which, along with quartz, are encountered in industrial operations and industrial products. Because the International Agency for Research on Cancer has designated “crystalline silica” as an IARC Group 2A (probable carcinogen) and quartz and cristobalite as a Group 1 (carcinogen), it is important to properly identify and quantify the silica phase in all materials used in production and encountered in products. Opal is a form of hydrated silica which is also encountered in industry. Although some forms of opal mimic cristobalite and tridymite, they are not truly crystalline. The term “silica” in the industrial sense is used to mean any material whose composition is SiO2 whether it is crystalline or noncrystalline. Some people also consider silica to include hydrated SiO2. There are many forms of SiO2 which have both long-range and short-range order and are recognized as crystalline phases among which are quartz, cristobalite, and tridymite. The hydrated silicas, on the other hand, pose an enigma. Only a few forms show sufficient long-range and short-range order to be considered crystalline. The mineral silhydrite is an example. Opal in all its forms lacks sufficient order to be considered crystalline. Even opal-C, which produces a X-ray pattern similar to the diffraction pattern of cristobalite, lacks not only sufficient order to be considered crystalline but also contains water in the structural make-up. This paper discusses a classification and nomenclature for these forms which is critical to proper regulation. It also reviews the recent literature on tridymite, cristobalite, and opal, and provides an extensive bibliography. Modern studies have shown that opal-A is disordered, but opal-CT and opal-C contain ordered domains that mimic stacked sequences of cristobalite and tridymite sheets such that X-ray patterns show features similar to the crystalline cristobalite and tridymite. There is debate on whether the ordered regions have lost the water that characterizes the opals. In fact, heating studies have shown that all opals show changes on heating characteristic of materials that lose water in the process. The TEM evidence showing domains in the range 10–30 nm in a matrix of disordered opal suggest that the proper term for this system is paracrystalline analogous to inorganic and organic polymers.

Pentastrontium bromidephosphate, Sr5(PO4)3Br, was prepared by solid state reaction. The crystal structure of polycrystalline Sr5(PO4)3Br was refined from X-ray powder diffraction data by the Rietveld method using the structure model of Sr5(PO4)3Cl single crystals. Sr5(PO4)3Br is isostructural with Sr5(PO4)3Cl. The space group is P63/m. The cell parameters are a0=9.9641(1) Å, c0=7.2070(1) Å, α=β=90°, γ=120°, Z=2, d(calc)=4.27 g/cm3, and d(expt)=4.10 g/cm3. Atomic parameters are given. Final values are Rp=10.9%, Rwp=14.3%, and S=1.28. The figure of merit is F30=58 (0.013, 39).

The main difficulty in the quantitative mineral analysis of rocks is connected with the variable nature of the mineral species. In the present paper a combined method (and a corresponding computer program) is proposed, which practically overcomes this difficulty. This method is based on linear equations, which are a combination of the chemical mass-balance equations with those of the quantitative X-ray diffractometry, and can perform (completely or partly) both the quantification and the chemical characterization of the minerals on several rock samples simultaneously, demanding only easily accessible initial information, such as: (i) major element (oxide) compositions for the samples; (ii) qualitative mineral composition of the samples; (iii) X-ray intensities for one or few nonoverlapped reflections of the crystalline minerals (not necessarily of all): (iv) some characteristic data for the phases (i.e., chemical composition data), if these are accurately known. Where it is possible the minerals may be expressed via end members. The samples may contain amorphous phases and/or phases without X-ray data. From the general case some very simple partial cases are derived, demanding less initial information. This method has the following advantages over the previous ones of similar philosophy: (i) drastic reduction of the number of required samples; (ii) sufficiency of equations for any analytical problem; (iii) possibility of performing partial analysis when a complete one is impossible; (iv) possibility of using the same end member in more than one solid solution. Analysis examples are given.

X-ray diffraction experiments performed on the compounds FeIINbIVF6 and CoIINbIVF6 have shown that they crystallize in the rhombohedral system, space group R3¯ with a cationic ordering. Unit cell parameters were determined: a=5.4201(8) Å, c=14.072(2) Å, V=357.8(1) Å, Z=3 for FeNbF6, and a=5.351(2) Å, c=13.960(6) Å, V=346.2(2) Å, Z=3 for CoNbF6. Synthesis and powder diffraction data are reported.

The X-ray powder diffraction pattern of the room temperature phase of Cd4GeSe6, a II4 □ IV VI6 semiconducting material, has been recorded and evaluated. This material crystallizes in the monoclinic space group Cc [No. 9] with a=12.847(3), b=7.407(2), c=12.854(2) Å, β=109.82(1)°, and Z=4. The powder diffraction pattern was also used to refine the crystal structure of this material employing the Rietveld method. The refinement of 56 parameters led to RWP=13.2%, RP=9.95% for 3751 step intensities and RB=7.05% and RF=5.20% for 833 reflections. Cd4GeSe6 can be considered a defect “adamantane-structure” material with a sphalerite-related superstructure.

2,4-dichloro-5-nitrobenzoic acid (C7H3NO4Cl2) has been investigated by means of X-ray powder diffraction. The title compound is monoclinic with unit-cell parameters a=13.761 (2), b=8.435 (1), c=7.684 (1) Å, β=99.85 (1)°, V=878.5 (1) Å3, Z=4, Dx=1.772 g/cm3, space group P21/a (14).

Combining the exhaustive indexing of triclinic powder diffraction patterns with a crystallographic determination of unit cell parameters from pinacoid and prism reflections yields unit cell parameters with realistic limits of error. Additionally a referee method has been developed by which the six reciprocal cell parameters of a triclinic phase are determined by solving an exhaustive set of linear simultaneous equations in six unknowns.

The powder diffraction data for 1-aminoanthraquinone at 295 K (P1¯, No. 2, Z=1) are given. The cell parameters found are a=8.205(1), b=8.396(1), c=3.7882(3) Å, α=93.46(1), β=92.57(1), γ=105.13(1)°. The crystal packing model is proposed giving Rb=0.095. The disordered molecule of 1-aminoanthraquinone occupies a special position on the inversion center.

Standard Reference Materials (SRMs) for determining instrumental line profiles should not exhibit measurable broadening from structural imperfections, but owing the effects of sample transparency and other geometrical effects, the quality of possible SRMs cannot necessarily be assessed satisfactorily with data from a conventional divergent-beam diffractometer. The problem of transparency can be avoided if parallel beam optics is used, as for instance on a synchrotron radiation powder diffraction station employing Parrish (Soller-type receiving slit assembly) geometry. Data from such a configuration are used to compare three SRMs commonly used in line-profile analysis.

The application of the Rietveld method to quantify mineral components of bauxite and lateritic samples was carried out in order to determine the ability of the method to obtain accurate mineralogical abundances for these materials. The method was initially applied to synthetic mixtures using both Cu and Co Kα radiations, and it was shown that Rietveld-derived data compared favourably with the weighed compositions. Application to two types of natural bauxite resulted in a high correlation between Rietveld predicted values and those calculated by proportioning peak intensities with chemical assays. The use of the whole pattern rather than selected peak intensities gives greater accuracy, confirmed by a strong correlation between derived oxide concentrations from XRF assays. Accuracy and precision were improved by the determination of isomorphous substitution of aluminum in goethite and hematite by refinement of unit cell dimensions. Importantly, the ability of the Rietveld program to successfully model several goethites with different levels of isomorphous substitution improved the correlation between predicted and calculated values. In addition, crystallinity and crystallite size that influence the reactivity of the mineral components can be derived from refined peak profiles.

Taking advantage of the feasibility to obtain well-prepared surfaces, an extensive work has been done in studying X-ray diffraction line broadening effects from flat polycrystalline samples of uranium and uranium alloys. The broadening analysis has been used as a semiquantitative method for measuring inhomogeneity of alloying, hardness, and residual thermal stresses. Good correlation between the microstrain and the hardness was found after heat treatments and cold work. A comparable correlation was found between the microstrain in the supersaturated α-uranium phase quenched from the γ region, and the concentration of the alloying elements. The measured microstrain in the supersaturated α-uranium phase was used as a quantitative value for determination of the solubility limit of Ta and W in γ-uranium. As a result of this study it was found that the limit of solubility is approximately 2.6 and 2.0 at. % for Ta and W, respectively.

The crystal structures of BaR2ZnO5, where R=La, Nd, Dy, Ho, and Y, were studied by neutron diffraction, and that of the Er analog was investigated by synchrotron X-ray diffraction. Two structure types were confirmed for this series of compounds and agreed with those reported in literature. The compounds with a smaller size of R (R=Dy, Ho, Y, and Er) are isostructural to the orthorhombic “green phase (BaY2CuO5)” compounds. The cell parameters for compounds with the R=Er to Dy range from a=7.0472(1) Å to 7.0944(1) Å, b=12.3022(1) Å to 12.3885(2) Å, and c=5.6958(1) Å to 5.7314(1) Å, respectively. R is 7-fold coordinated inside a monocapped trigonal prism. These prisms share edges to form wavelike chains parallel to the long b-axis. The Ba atoms reside in 11-fold coordinated cages. The compounds which contain a larger size R (R=La and Nd) crystallize in the tetragonal I4/mcm space group, but are not isostructural to the “brown phases” BaR2CuO5. The lattice parameters for the La and Nd analogs are a=6.9118(1) Å, c=11.6002(2) Å for BaLa2ZnO5, and a=6.7608(1) Å and c=11.5442(2) Å for BaLa2ZnO5. The structure consists of ZnO4 tetrahedral groups (instead of planar CuO4 groups as found in the brown phase) with Ba ions inserted in between. The structure can be viewed as consisting of alternate layers of Zn-Ba-O and Nd-O extending infinitely in the xy plane and perpendicular to the z-axis.

The usefulness of a high X-ray flux instrument to improve the accuracy of a powder diffraction pattern is demonstrated. In this case, very weak reflections of a well-characterized and well-known natural mineral can be detected by an often-used X-ray rotating anode diffractometer. High purity natural dolomite, CaMg(CO3)2, for example, was used to produce a slightly more comprehensive indexed X-ray powder diffraction. The powder pattern obtained in this study was compared with that of the reported high quality PDF pattern (36-426, with “*” mark) and that of a calculated pattern derived from single crystal structure data. A very weak 003 reflection at low angle and many weak reflections at high angles, not reported in the PDF pattern, were successfully identified using this high-power X-ray instrument. Unit cell parameters were determined to be a=4.8090±0.0001 Å and c=16.0182±0.0003 Å, which were in good agreement with the extant PDF pattern. Accuracy of the relative intensities between the measured and calculated patterns was apparently somewhat improved in this study, probably also attained through less preferred orientation and the higher purity of the sample used.

Two compounds, [Co(NH3)5CO3]NO3·1/2H2O (labeled A) and [Co(NH3)4CO3]NO3·1/2H2O (labeled B), were obtained and characterized by X-ray powder diffraction. The samples were indexed using the programs TREOR90 and DICVOL91. In a monoclinic setting, the cell parameters are a=7.6661(3) Å, b=9.6212(3) Å, c=7.0725(4) Å, β=106.261(4)°, V=500.78 Å3, M20=36, F30=65 (0.0106, 44) for A and a=10.5623(5) Å, b=22.7304(18) Å, c=7.5174(5) Å, β=91.350(5)°, V=1804.31 Å3, M20=36, F30=82 (0.0071, 52) for B. The space group is probably P21/m(11) for A and P21/n(14) for B according to their reflection conditions.