The crystal structure of the natural zeolite garronite from Goble, Oregon has been refined using high resolution synchrotron X-ray powder diffraction data. Garronite has the same tetrahedral aluminosilicate framework as gismondine [GIS], and earlier structural models indicated a strong tetragonal pseudosymmetry. Proposed models in the literature were based on the I4¯m2 and I41/a space groups, on account of symmetry lowering from the topological I41/amd space due to partial cation/water molecule order in the zeolitic cavities. Test structure analysis has been performed in all possible space subgroups including monoclinic space groups, and the refinement has been successfully carried out in space group I2/a (C2/c). The resulting monoclinic structure model is to be preferred over the tetragonal ones on the basis of: (1) lower agreement indices of the refinement; (2) a chemically sound framework geometry; and (3) a more satisfactory interpretation of the Ca atoms coordination in the extraframework cages.

Most modern X-ray powder diffraction work is carried out using the parafocusing powder diffractometer. The typical instrument employs a mechanical goniometer to control the basic geometric movements required for recording diffraction data. Modern trends toward high speed data acquisition and computerized analytical procedures make the need for a well designed and well maintained goniometer system increasingly critical. This paper reviews the mechanical design parameters of typical goniometer systems in light of their influence on the accuracy and precision obtainable in diffraction data. Data on typical vertical and horizontal goniometer systems are compared, along with bench tests using a state of the art “anti-backlash” gearing system. By examining the nature of the errors typically encountered in today's goniometers it becomes evident why the next major improvement will likely be in software rather than hardware.

Two complexes of gallium with 3-hydroxy-4-pyrones were synthesized as potential pharmaceutical compounds for oral administration. These compounds were analyzed by powder X-ray diffraction followed by computer indexing of the data. The first compound, tris(3-hydroxy-2-methyl-4-pyronato)gallium [Ga(C6H5O3)3], was found to be orthorhombic, a = 18.500(2), b = 16.948(2), c = 12.012(2) Å, V = 3766(1) Å3, Z = 8, Dm = 1.56(5), Dx = 1.570. The compound appears closely analogous to a similar compound containing Al instead of Ga, which crystallizes in space group Pbca. The second compound, tris(3-hydroxy-2-ethyl-4-pyronato)gallium [Ga(C7H7O3)3], was found to be monoclinic, a = 31.634(2), b = 8.7662(5), c = 7.8982(5) Å, β = 103.240(6)°, V = 2132.0(5) Å3, Z = 4, Dm = 1.50(5), Dx = 1.517, with a primitive space group.

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 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.

The crystal structures of Mek[Fe(CN)6];l·mH2O where Me = Cu, Ni and Co, have been refined from X-ray (CuKa) powder diffraction data by means of Rietveld analyses in space group . The Fe and Me ions are octahedrally coordinated by C and N atoms respectively, forming three-dimensional bimetallic networks with the CN-groups as bridging ligands. The Me(l) sites (k = 2, l=1) and the Fe sites (k = 3, l = 2) are partially occupied. Water oxygens were placed in alternative, empty metal sites.

Powder X-ray and optical data have been recorded for a sample of exceptionally rare earth-poor eudialyte (Na12(Ca, REE)6(Fe2+,Mn,Mg)3Zr3(Zr,Nb)x[Si9O27−y(OH)y]2[Si3O9]2(C1,F)z, with x = 0. 1–0.9, y = 1–3 and z = 0.7–1.4) from a pegmatitic vein associated with the peralkaline Windy Fork granite in the north–central Alaska range. The eudialyte is uniaxial positive with ω= 1.6062(2), ε= 1.6138 (3) and microprobe analyses indicate that the sum of REE + Yis less than 0.1 weight percent. Refined unit cell dimensions are: a = 14.2572(4), c = 30.1338(27), Dx= 2.67, F30= 128 (0.006, 42), M20= 76. An indexed powder diffraction pattern is given.

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 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.

Don Hanawalt died three years ago this June. To those of us who were privileged to know him he was a special person, a man of boundless energy and tireless enthusiasm. In a very real sense Don was a founder in the use of the powder diffraction as a practical laboratory technique. His pioneering contributions included the universally employed search method which, today, still bears his name, and which really established qualitative phase identification. To Don's chagrin, his work never received the same enthusiastic acceptance among chemists that it did by mineralogists and metallurgists. Several months before Don died, Richard Rose of the Journal Staff interviewed Don with the idea of writing an article for the Journal covering Don's contributions to the field of powder diffraction in general, and his work within the International Centre in particular. Because of Don's untimely demise the work was never completed… but in order that a description of Don's interest and work in the powder diffraction field should be recorded, we have taken the tape transcripts and edited them into what we hope will be a cohesive, if somewhat abbreviated, story. Where possible, we have retained the actual language of the interview. Where necessary, minor corrections have been made to some of the dates mentioned by Don. The interview starts by reviewing the early days of X-ray analysis.

Rietveld quantitative X-ray diffraction analysis of the fly ash Standard Reference Materials (SRMs) issued by the National Institute of Standards and Technologies was performed. A rutile (TiO2) internal standard was used to enable quantitation of the glass content, which ranged from 65% to 78% by weight. The GSAS Rietveld code was employed. Precision was obtained by performing six replicates of an analysis, and accuracy was estimated using mixtures of fly ash crystalline phases and an amorphous phase. The three low-calcium (ASTM Class F) fly ashes (SRM 1633b, 2689 and 2690) contained four crystalline phases: quartz, mullite, hematite, and magnetite. SRM 1633b also contained a detectable level of gypsum, which is not common for this type of fly ash. The high-calcium (ASTM Class C) fly ash, SRM 2691, had eleven crystalline phases and presented a challenge for the version of GSAS employed, which permits refinement of only nine crystalline phases. A method of analyzing different groups of nine phases and averaging the results was developed, and tested satisfactorily with an eleven-phase simulated fly ash. The results were compared to reference intensity ratio method semiquantitative analyses reported for most of these SRMs a decade ago.

Features of the powder diffraction patterns of known polytype-like modifications of Ca3GeO5, such as 2H, 9R and 24R types, and a monoclinic polymorph have been studied by means of the patterns calculated based on their crystal structures. The result has provided keys to identify them when they coexist in the same synthetic product. Accounts have been given on the crystallographic features of the building layer and rules for layer stackings of the modifications in general. Any modification may then be constructed to predict its powder diffraction pattern.