A unique file structure and search algorithm have been developed for the purpose of obtaining matches between experimental electron diffraction and qualitative energy dispersive X-ray compositional data from an unknown crystalline phase and the reference data in the JCPDS Powder Diffraction File. The reference data for over 32,000 inorganic compounds from sets 1–33 were compressed and stored in binary format as bit pattern maps. The entire data set and searching programs require less than 4 Mbyte and retain the precision appropriate for electron diffraction analysis. The search algorithm, written in both RT-11 FORTRAN and Flextran, is based on pattern matching between bit maps obtained for the unknown and reference compounds for both composition and diffraction data. Special attention is given to double diffraction effects commonly encountered in electron diffraction analysis. The programs run on an interactive basis on a microcomputer dedicated to the X-ray energy dispersive spectrometer on an analytical electron microscope. A typical search takes about 15 seconds to run and extracts about 10–15 different compounds.

In conventional multiphase Rietveld refinement, now being used for quantitative phase determination, the crystal structure of each phase needs to be known in order to generate a calculated standard pattern of the phase to be refined against the measured XRD pattern. This is a disadvantage when the structural data for a phase are imperfect or unknown and may prevent an analysis.

A method is given whereby a phase with an imperfectly known or unknown crystal structure can be included in a multiphase Rietveld refinement, with other well-characterised phases, by use of an empirical or “observed” hkl file for that phase, with the SIROQUANT software package. The amplitudes 1F(hkl)1 in the empirical hkl file of the phase generate a reference profile for it which agrees with a measured standard pattern of the phase. Methods are given for the creation and scaling of empirical or “observed” phase hkl datasets. The Rietveld variable parameters (preferred orientation, linewidth, lineshape and unit cell) are refinable in the usual way for a phase with an empirical hkl dataset.

The X-Ray Powder Data File (XRPDF) enables one to identify the compounds in a sample. More often than not, however, a semi-quantitative analysis is wanted. Visual inspection of the pattern may give a vague impression of the composition, but the errors of such a result are usually not within reasonable limits. Clearly a less subjective and more accurate method is wanted. If the necessary data are printed on the cards, such a method will greatly enlarge the usefulness of the File.

The structure of Ba7Cl2F12 has been determined ab initio from conventional X-ray powder diffraction data by the “heavy atom” method. The cell is hexagonal (space group P6¯, Z=1), with a=10.6373(2) Å and c=4.1724(2) Å. Refinement of 38 parameters by the Rietveld method, using 278 reflections, leads to cRwp=0.173, cRp=0.135, and RB=0.054. The structure has common characteristics with that of the other BaF2-rich fluorochloride, Ba12Cl5F19. In both phases Ba2+ ions lie in tricapped trigonal prisms formed by nine halide ions, and Cl− ions occupy the center of trigonal prisms of Ba2+ ions. F− ions are located in cationic tetrahedra or square pyramids.

The decomposition reactions of two zirconium hydroxide nitrates Zr(OH)2(NO3)2·(4+x)H2O and α-Zr(OH)2 (NO3)2·(1+x)H2O (0≤x≤1) have been studied by thermogravimetric analysis and high-temperature X-ray powder diffractometry (HTXRD), in nitrogen gas environment. The decomposition reaction sequences were clearly displayed by the HTXRD technique. They are different for the two precursors, except the formation of amorphous zirconia at low temperature (200 °C) and crystalline zirconia at about 390 °C. Three modifications of Zr(OH)2(NO3)2·H2O (α,β,γ) were identified. Their X-ray powder diffraction patterns were indexed by the successive dichotomy method. The unit cells are triclinic and present some parametric and volumetric similarities from each other and also with that of their precursor. Moreover, the thermal decomposition sequences of Zr(OH)2(NO3)2·(4+x)H2O and α-Zr(OH)2(NO3)2·(1+x)H2O include the formation of anhydrous oxide nitrate ZrO(NO3)2 and anhydrous hydroxide nitrate Zr(OH)2(NO3)2, respectively.

A nonlinear optical material 4-(N,N-dimethylamino)-3-acetamidonitrobenzene, (CH3)2NC6H3NO2NHCOCH3, has been characterized by X-ray powder diffractometer method. The experimental 2θ values corrected for systematic errors, the relative intensities, values of dexp and the Miller indices of the 46 peaks observed in the 5° to 51° 2θ range are reported. The powder diffraction data have been evaluated, and the figure of merit is F30 = 36.6 (0.016, 51). The unit cell parameter least-squares refined from 38 non-overlapping peaks of the monoclinic compound with a P21 space group are: a = 4.792(1)Å, b = 13.055(2)Å, c = 8.735(1)Å, β = 94.43(2)°, V = 544.8(1)Å3, Z = 2, and Dx = 1.36 gm/cm3. The powder diffraction results are in a good agreement with those obtained from single-crystal structure data.

External standard and internal standard calibrations are important procedures for achieving high accuracy in X-ray powder diffraction studies. The theoretical basis as well as procedures for obtaining calibration curves are given. Methods and examples of selecting Standard Reference Materials (SRMs) which are produced and issued by the National Bureau of Standards (NBS), and procedures of sample preparation with these standards are also described. Three examples are presented to indicate the value of using SRMs.

A cover for Scintag's six and twelve-position sample changers was designed and constructed to provide an inert atmosphere for samples during diffraction batch runs. The cover is equipped with inlet and outlet gas ports and fits over the top of the sample changer. Using dry nitrogen gas fed into the inlet of the cover, a sample of lithium bromide was protected from atmospheric moisture for greater than 18 h. The cover uses a thin Mylar window that gives greater than 95% transparency for copper K-alpha X-rays. The cover is a simple device that allows our lab to run multiple moisture-sensitive samples in a batch mode. The simple approach and materials used in the construction of the cover could be applied to other brands of powder diffractometers.

Nickel Cimetidine Chloride, Ni(C10H16SN6)2Cl2·2H2O has been investigated by means of X-ray powder diffraction. Unit cell dimensions were determined by indexing programs, from diffractometer data obtained with copper radiation. A primitive monoclinic cell was found: a = 11.836(3)Å, b = 13.322(5)Å, c = 10.487(2)Å, β = 113.08 (2)°, Z = 2, Dx = 1.462 g/cm3, M.W. = 670.32. These data are consistent with values reported in the literature for other cimetidine complexes.

MeT2O6 (M = Ce, Th) are monoclinic, space group P21/n (No. 14). The cell dimensions for CeTe2O6 are a = 7.0190(7), b = 11.0423(6), c = 7.3319(8)Å and β = 108.00(8)° and for ThTe2O6 cell dimensions are a = 7.1934(4), b = 11.2310(6), c = 7.4650(2) Å and β= 108.04(6)°.

The new compound, KCr3(SO4)2(OH)6, was prepared by low-hydrothermal synthesis. The structure was refined by the Rietveld technique in space group (Z = 3), a =7.2416(3) Å, c = 17.0788(9) Å, V = 775.63 Å3, Rp = 7.7, Rwp =10.1, RB = 6.8. The compound is isotypic with alunite, KAl3(SO4)2(OH)6. The temperature of decomposition under nitrogen atmosphere to a hitherto unknown form is about 550 K. The water content of alunite-type compounds is discussed.

We have examined the barium ferrite powder X-ray diffraction patterns in the PDF using experimental and calculated diffractograms. An improved calculated diffractogram is proposed. The result indicates that the primary peak of barium ferrite is not (107) but is (114).