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.

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.

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 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.

Samples of the mineral ferroan clinozoisite from three localities of Greece (Paranesti-Drama, Xanthi, and Petritsi-Serres), with chemical formula Ca2Al3−xFexSi3O13H (x=0.55, 0.58, and 0.46, respectively), were measured by X-ray powder diffraction, using CoKa radiation. The PDF and bibliographic information were used in order to identify additional phases in the samples. Refinement combined with PDF resulted in the following: ferroan clinozoisite (100%) for the first sample, ferroan clinozoisite (97%) and malladrite (3%) for the second one, and ferroan clinozoisite (75%), clinopyroxene (20%), and malladrite (5%) for the third one. The crystal structure refinement was performed by the “Powder profile analysis (Rietveld)”. P21/m space group was chosen for the ferroan clinozoisite phases, with unit cell constants a=8.8919(5) Å, b=5.6260(3) Å, c=10.1570(6) Å, β=115.418(3)° (Paranesti), a=8.8944(7) Å, b=5.6394(4) Å, c=10.1626(8) Å, β=115.400(5)° (Xanthi) a=8.8965(8) Å, b=5.6372(4) Å, c=10.1595(9) Å, β=115.411(6)° (Petritsi) almost similar for the three samples, while the final R-p factors were 0.069, 0.064, and 0.063, respectively.

Three new mixed oxides having the nasicon structure and containing arsenic(V) as tetrahedral ion were prepared and X-ray analyzed. The stoichiometry of the three phases can be expressed by the comprehensive notation MeZr2As(3−x)PxO12 where Me stands for Na+ or K+, x equals to 0 and 1.5 when Me=Na, while x equals to 1.5 when Me=K. For two other compositions of the above series, the powder patterns were calculated on the basis of the structural data from single crystal determinations, thus permitting us to complete the characterization of the solids, with nasicon framework, deriving from MeZr2P3O12 (Me=Na+, K+) by partial (50%) or complete (100%) substitution of As for P.

Key words: nasicon, ionic conductors, phosphates, arsenates

The crystal structure of the solid solution alkaline earth plumbate phase Sr4−xCaxPb2O8 was investigated using the X-ray Rietveld technique for x=1, 2, and 3. The lattice parameters a, b, c, and V were found to decrease linearly as the Sr at site 4h was replaced by Ca. The structure features chains of edge-sharing PbO6 octahedra, linked by seven-coordinated (Ca/Sr)–O monocapped trigonal prisms. The structure is similar to that of Pb3O4, which can be reformulated as Pb2IIPbIVO4. X-ray diffraction patterns for the solid solution members SrCa3Pb2O8, Sr2Ca2Pb2O8, and Sr3CaPb2O8 were prepared for inclusion in the Powder Diffraction File.

The crystal structure of the rare earth (RE) compound CeFeGe3 has been studied by X-ray powder diffraction and refined by the Rietveld profile fitting method. The compound has the tetragonal BaNiSn3-type structure, space group I4mm (No. 107) a=4.3294(1) Å, c=9.9444(3) Å, V=186.39 Å3, Z=2, and Dx=7.372 g·cm−3. The figure of merit FN for the powder data is F30=184.3(0.0037,44). The structure refinement was performed with 106 reflections and led to Rp=13.2% and Rwp=18.2%. Powder data are given.

Two structurally related compounds, Tl3Li(MoO4)2 and Tl3Li(WO4)2, have been synthesized by solid state reaction. Space group (P63mc) and unit-cell parameters [a(Å)=6.00392(3); c(Å)=15.8203(1) and a(Å)=6.03484(3); c(Å)=15.81759(9), respectively, for Tl3Li(MoO4)2 and Tl3Li(WO4)2] were determined. Powder diffraction data for each phase are reported.

X-ray powder-diffraction data were collected for a new iron phosphate, Fe(PO4)·0.5H2O, obtained by reducing FePO4 with oxalic acid at 220 °C in the presence of water vapor and oxygen. The crystal system was determined to be orthorhombic with unit-cell parameters a=15.991(6) Å, b=20.156(7) Å, and c=7.223(2) Å.

The results of computer simulations of the absorption of diffracted X-rays in single-phase powders measured at cylindrical (or Debye–Scherrer capillary) geometry taking into consideration the size of the powder particles are presented. The samples are simulated by random dense packings of equal spheres. The calculations are carried out for different values of the ratio, Da, of particle size to cylinder diameter, the product, κ, of linear absorption coefficient and cylinder radius and the scattering angle 2θ. Strong deviations of the absorption factor from the values for the ideal case of very fine particles are found in the region 0≤2θ≤30°, and for medium and high values of κ,(κ≥5) and Da (Da≥0.002). The consequences for the experiment are discussed.