X-ray powder diffraction is one of the most sensitive methods for the analysis of crystalline forms of silica. In addition to detection and quantification, it can determine the specific crystalline species in the sample. The principal limitations of the method depend on the effective volume of the sample in the X-ray beam and the number of crystallites in the proper orientation to diffract. Detection limits are usually reported as 2 μg in thin-film filter mounts and 0.1% in bulk samples that are free of interference from associated minerals. Filter methods are most often used for air quality monitoring and several standardized procedures have been certified. Standard procedures for bulk samples are difficult to certify because of the variability of the matrices and their potential interferences. All of the methods of quantification require calibration with known samples of quartz or cristobalite. Certification of standard samples involves characterization of the particle and crystallite size and size distribution and amorphous content as well as determining the X-ray diffraction response. Although quartz is readily available and cristobalite is easy to synthesize, preparation of quantities of sufficient uniformity and stability is a limiting factor in certifying such samples for reasonable costs. Conventional diffraction equipment can be used for crystalline silica analysis at the present detection limits required by safety standards. Relatively simple modifications of the diffractometer will increase its sensitivity to small amounts of silica and improve the lower limits of quantification.

X-ray powder diffraction data are reported for α-brass with the composition Cu: 63.44±0.04 wt %, Zn: 36.45±0.06 wt %. No valid reference card for this material is present in the JCPDS-ICDD database. The investigated brass composition is cubic (Fm3m) with a0: 3.69612±0.00014 Å, unit cell volume: 50.4938±0.0058 Å3, density calculated: 8.44±0.05 g/cm3, density measured: 8.43±0.03 g/cm3. The X-ray diffraction pattern presented resembles that of deleted reference card 6-657 in great detail.

We have calculated X-ray powder-diffraction data for schoepite, [(UO2)8O2(OH)12](H2O)12, using unit-cell and atomic parameters from the crystal structure (a 14.337, b 16.813, c 14.781, Z=4, Dx=4.87 gcm−3). Schoepite crystallizes in space group P21ca but is strongly pseudo- centrosymmetric, and observed reflections (Irel>0.1%) conform to space group Pbca. The six strongest reflections for schoepite are [d(Å), hkl (relative intensity)] 7.365, 002 (100), 3.253, 242 (55), 3.626, 240 (36), 3.223, 402 (25), 3.683, 004 (20), 2.584, 244 (18). The calculated intensities of reflections that distinguish space group Pbca from space group Pbna (the space group of metaschoepite), i.e., h0l with h odd and l even, are weak, and may not be evident in experimental powder patterns. The a axis of schoepite (14.34 Å) is significantly longer than that of synthetic metaschoepite (13.98 Å), and the two phases can best be distinguished by their unit-cell parameters. However, potential overlap of the strongest reflections can make identification and unit-cell determination difficult, especially for fine-grained material. Natural samples commonly contain intergrowths of schoepite, metaschoepite, and dehydrated schoepite. The calculated powder pattern for schoepite agrees well with data reported for natural schoepite (PDF 13-241) but shows discrepancies with the data from synthesis products. Data for “synthetic schoepite” indicate that this product was a mixture. Powder data labeled “paraschoepite” in the Powder Diffraction File do not correspond to the mineral of that name.

The crystal structure of low temperature NaNiO2 has been refined by Rietveld methods using powder X-ray diffraction and neutron scattering data. The starting model was based on parameters that had been obtained earlier by X-ray film methods. At room temperature NaNiO2 is monoclinic, C2/m, a=0.53192(2), b=0.28451(1), c=0.55826(4) nm, β=110.449(2)°. NaNiO2 has a layered structure. The Ni–O layer is formed by edge sharing of Jahn–Teller elonganted NiO6 octahedra with Ni–O distances of 0.1911(2) nm and 0.2144(4) nm. The Na ions between these layers also exhibit a distorted octahedral coordination with Na–O distances of 0.2328(2) nm and 0.2369(4) nm. The final R values were Rwp=0.069, RI=0.059, Rexp=0.059 for the neutron and Rwp=0.032, RI=0.034, Rexp=0.017 for the X-ray data.

Rietveld analysis of X-ray powder diffraction data was performed on SmBa4Cu3O8.5+δ, which was synthesized from precursors Sm2O3, BaO2, and CuO at 1000 °C in an oxygen atmosphere. SmBa4Cu3O8.5+δ has a cubic perovskite-related structure that is isostructural with YBa4Cu3O8.5+δ, and a doubled perovskite unit cell parameter of 8.177 90±0.000 04 Å.

A comparison of X-ray powder diffraction and electron probe microanalyses on samples of Na- and K-doped Bi4V2O11 (BIMEVOX) solid electrolytes indicates some of the problems associated with using XRD to assess phase purity, especially in materials of variable composition such as BIMEVOXes. In this study both the Na- and K-doped materials appeared phase pure by XRD. EPMA indicated the Na-doped materials to be single phase with their expected compositions while the K-containing materials were not phase pure with very little K present in the main BIMEVOX phase.

A significant feature of the atomic structure of the intermetallic compounds RhAl2.63 (Pearson-Parthé symbol cP(34-5) [notation according to Parthé et al. (1993)], space group P23), IrAl2.75 (cP(34-4), P23) and AuZn3 (cP32, Pm3¯n) is the occurrence of icosahedral clusters. Least squares refined lattice parameters and powder diffraction data are reported for these homeotypic phases.

X-ray powder diffraction data of CoSi are reported. The sample was prepared by an arc melting process and has a cubic structure (space group P213, space group No. 198) with lattice parameter a=4.4427 Å, Dx=6.591 gcm−3, Z=4, and I/Ic=1.03.

X-ray powder diffraction data of BaFCl are reported for 2θ from 5° to 150° at 25 °C. Strain-free and dendrite-free single crystals of BaFCl, grown by flux method with KCl as flux, were powdered for recording this data. BaFCl is tetragonal, space group P4/nmm, with a=4.3964(1) Å and c=7.2315(3) Å.

X-ray powder diffraction data and refined unit cell parameters for three compounds found during experimental determination of the BaO:Fe2O3:TiO2 phase diagram are reported here. All three phases crystallize in space group C2/m (No. 12). Ba2Fe2Ti4O13 (“2:1:4”) is isostructural with K2Ti6O13 and Ba2ZnTi5O13: a=15.1939(9), b=3.8912(3), c=9.1244(5) Å, β=98.456(5)°; Z=2, ρcalc=4.890 g/cc. Ba3Fe10TiO20 (“3:5:1”) is structurally analogous to its aluminum congener Ba3Al10TiO20: a=15.336(1), b=11.7986(9), c=5.1700(4) Å, β=91.220(6)° (I2/m setting); Z=2, ρcalc=4.750 g/cc. Ba4Fe2Ti10O27 (“4:1:10”) is also isostructural with its aluminum analog Ba4Al2Ti10O27: a=19.799(1), b=11.4324(6), c=9.8936(6) Å, β=109.146(4)° (C2/m); Z=4, ρcalc=4.934 g/cc. The 2:1:4 and 3:5:1 compounds adopt open-framework type structures while the 4:1:10 phase exhibits an eight-layer close-packed arrangement.