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Mixed lead chloride oxalate, Pb2Cl2(C2O4), has been obtained in a polycrystalline form in the course of a study on precursors of nanocrystalline PZT-type oxides. Its crystal structure has been solved ab initiofrom powder diffraction data collected using a monochromatic radiation from a conventional X-ray source. The symmetry is monoclinic, space group C2/m, the cell dimensions are a=5.9411(3) ?, b=5.8714(4) ?, c=9.4212(4) ?, ?=95.232(4)? and Z=2. The structure consists of a stacking of complex double sheets, built from lead polyhedra, parallel to (001) and connected together through oxalate groups. The lead atom is nine-fold coordinated by four O atoms from one bidentate and two monodentate oxalate groups and five Cl atoms. The polyhedron can be described as a highly distorted square antiprism mono-capped by a Cl atom. The thermal behavior of lead chloride oxalate, in vacuum and in air, is carefully described from temperature-dependent powder diffraction and thermogravimetric measurements. It is shown that reaction pathways are complicated by the identification of various oxide chloride phases.

The crystal structure of the layered cadmium hydroxide sulfate Cd4SO4(OH)6.1.5H2O has been solved from X-ray powder diffraction data. The compound crystallizes with hexagonal symmetry, a=9.145(1) ?, c=15.099(3) ?, V=1093.5 ?3, Z=4, space group P63. Due to the unusual environment of one cadmium atom and to the fact that a suitable thin tabular crystal could be found later, a single-crystal X-ray diffraction experiment was also carried out. In both cases the structure was solved applying direct-methods. The refinements converged to the residual factors Rwp=0.152 and RF=0.059 from the powder data and R1=0.058 and wR=0.165 for the single crystal data case. The structure is built from brucite-type layers based on CdO6octahedra, in which one-seventh of the octahedral sites are empty. Directly above and below these empty sites, two additional octahedrically coordinated Cd atoms are located. The crystal chemistry of the cadmium hydroxide sulfate family is discussed.

A new mixed lead thorium phosphate, Pb0.5Th2(PO4)3, has been isolated in the system PbO?ThO2?P2O5. Its crystal structure (monoclinic symmetry, a=17.459(1) ?, b=6.8451(4) ?, c=8.1438(5) ?, ?=101.247(5)?, space group C2/c) has been determined from conventional monochromatic X-ray powder diffraction data. The structure is related to the MITh2(PO4)3structure type. Lead atoms are located in the channels parallel to the caxis, out of the twofold axis for 0.97 ?, and are statistically distributed on a quarter of crystallographic positions. The thermal stability of this material is greater than that of the monazite-type compound PbTh(PO4)2.

AbstractA comparison between the results of ab initiostructure determination from X-ray powder diffraction data of a new cadmium hydroxide nitrate, Cd5(OH)8(NO3)2?2H2O (SGC2/m), and those obtained from single crystal data is presented. The powder diffraction pattern has been analysed by an indexing method and fitting techniques. A total of 119 unambiguously indexed reflections has been extracted and used in subsequent treatment. The power of powder techniques to index the pattern and to find the structure model by normal Patterson and Fourier methods is clearly shown. The refinement of approximate coordinates has been carried out by the Rietveld method (444 reflections). The comparison of results with those obtained from single crystal data (2218 reflections) shows that the precision of positional parameter values is lower by a factor of 10, on average, in the powder study. These results are discussed in terms of crystallographic parameters (number of reflections used, number of parameters to refine, contrast between atoms) and, also, in terms of sample dependent properties (preferred orientation effect, impurity). Finally, the crystal structure has been derived from powder data with a precision probably sufficient for most purposes.

An analysis of the microstructure of nanocrystalline magnesium oxide produced by thermal decomposition of magnesium oxalate, in the temperature range 500 ?C?1200 ?C, is described. The study is based on diffraction line broadening analysis carried out with the integral breadth (Langford) and Fourier methods, combined with the pattern decomposition technique. Additionally, the whole pattern matching method is also applied. No marked line broadening anisotropy is observed in the patterns. It is shown that the nanopowders are characterized by minimal strain and that crystallites have an average spherical shape. Volume-weighted and area-weighted apparent sizes are in the ranges 98?480 ? and 72?282 ?, respectively, within the temperature range considered. The results obtained from line broadening analysis are compared to those observed with scanning electron microscopy and surface area measurements. A satisfactory agreement is found between sizes derived from the different techniques.

An analysis of the microstructure of nanocrystalline yttrium oxide produced by thermal decomposition of a double oxalate yttrium and ammonium, at temperatures in the range 600 ?C to 900 ?C, is described. The study is based on line broadening analysis carried out with the (Voigt/Langford) integral breadth and Fourier methods combined with the pattern decomposition technique. Due to the line overlap arising from the density of diffraction lines, the whole pattern refinement method (pattern matching and Rietveld approaches) is also applied. No marked line broadening anisotropy is observed in the patterns. It is shown that for the two samples prepared at the highest temperatures the results are similar whatever the method used and the material can be considered as strain free. For the two lowest temperatures only the whole pattern refinement method is applied. The results suggest that a small amount of lattice microdistortion is present in these two last samples. It is shown that the crystallite growth varies exponentially with temperature. The results obtained from line broadening analysis are compared to those observed with scanning electron microscopy, from which a good accordance is noted between the two techniques.

A new variety of ammonium lanthanum sulfate, ?-(NH4)La(SO4)2, was synthesized hydrothermally. The crystal structure was solved ab initiofrom powder diffraction data collected using a conventional X-ray source. The powder diffraction pattern was indexed by the successive dichotomy method: The symmetry is monoclinic, space group Pn, cell dimensions a=6.9365(4) ?, b=9.0055(5) ?, c=5.4541(4) ?, ?=90.672(8)?, V=340.68(3) ?3and Z=2 [M20=65, F30=124(0.0071,34)]. Direct methods were used for structure solution, and refinement of the atomic coordinates was carried out by the Rietveld method (RF=0.061, Rwp=0.099). The structure contains anionic layers built from lanthanum atoms ninefold coordinated to monodentate and bidentate sulfate oxygen atoms. Ammonium groups, which provide hydrogen bonds, are located between the layers. The crystal structure contrasts with that of the ? phase, which is less dense by a factor of 4.4%.

Three phosphates, MIBaIn2(PO4)3with MI=Na, K, Cs, isostructural to the langbeinite structure, have been studied from powder diffraction data collected with monochromatic radiation obtained from a conventional X-ray source. Precise powder data are reported, as well as cell parameters, i.e., a=10.026 08(9) ?, a=10.121 57(13) ? and a=10.226 94(9) ? for MI=Na, K and Cs, respectively. A Rietveld refinement has been carried out (space group P213), with final RFfactors, 0.061, 0.041 and 0.027, and Rwpfactors, 0.196, 0.142 and 0.129, for MI=Na, K and Cs, respectively. There are two octahedrally coordinated In3+ions in the asymmetric unit and the final refinements suggest disorder on the two sites of the MI/Ba sublattice.

AbstractA novel approach to the determination of crystallite size and lattice strain by means of Total Pattern Analysisis described. Parameters to define the position, magnitude, breadth and shape of individual peaks are obtained by an adaptation of the pattern fitting program of Sonneveld and Visser (J. Appl. Cryst.8, 1?7, 1975). A rapid assessment of the nature of the specimen broadening is given by a Williamson-Hall Plot. This leads to a more detailed study of line breadths by, for example, Voigt analysis applied to several orders of reflections or to single lines. Preliminary results are given for the application of this procedure to ?size only? and ?size-strain? samples of ZnO.

The thermal decomposition of barium bis(citrato)oxotitanate citrate heptahydrate, a molecular precursor of BaTiO3fine powders is studied by temperature-dependent x-ray powder diffraction and thermogravimetry. A thorough investigation of the dehydration stage is presented. Three crystalline phases containing seven, three, and two water molecules, respectively, are identified from their powder diffraction pattern. The results of pattern indexing are presented and discussed in terms of parameter relationships.

An analysis of the microstructure of nanocrystalline cerium oxide produced by thermal decomposition of cerium (IV) oxide nitrate at temperatures in the range 230? to 960 ?C is described. Parameters describing the breadths and shape of X-ray diffraction line profiles were obtained by means of pattern decomposition and a method based on the Voigt function was used to obtain information on the temperature dependence of the microstructure. No marked anisotropy in size and strain broadening was observed. It was found that the crystallites are on average spherical, the dimensions increasing significantly with formation temperature, while microstrains decrease with annealing temperature. The results of size determinations were compared with SEM measurements. They suggest a competition between the crystallite growth and ?particle? growth processes in the initial sintering of the loosely packed cerium oxide powder.

The structures of two high-pressure tungsten oxides, previously studied by high-resolution electron microscopy, were confirmed by Rietveld refinement based on X-ray powder diffraction data. The phases have identical stoichiometry, W3O8, and extremely narrow 00lreflections in common. The microstructure of the dominant phase was investigated by means of X-ray powder diffraction pattern decomposition. A Williamson?Hall plot revealed that all lines, except the 00lreflections, were broadened solely due to the crystallite size effect. A cylindrical model is used to describe the average form of the coherently diffracting domains. The height of the cylinder, whose axis is colinear with the crystallographic cparameter of both phases, is considered ?infinite,? and the average diameter of the cylinder model is 655(22) ?. A quantitative confirmation is obtained from electron microscopy.

A task group of the JCPDS?International Center for Diffraction Data (ICDD) was established with the charge of investigating the use of silver behenate, CH3(CH2)20COO?Ag, as a possible low-angle calibration standard for powder diffraction applications. Utilizing several data collection and analysis techniques, long-period spacing (d001) values with a range of 58.219?58.480 ? were obtained. Using the same collected data and one data analysis refinement calculation method resulted in dm values with a range of 58.303?58.425 ?. Data collected using a silicon internal standard and the same singular data analysis calculation method provided d001values with a range of 58.363?58.381 ?.

A new amine zinc hydroxide nitrate has been synthesized and investigated by means of X-ray powder diffraction. The monoclinic unit cell dimensions are a= 20.781(3) ?, b= 6.2151(9) ?, c= 5.4952(6) ?, ?= 92.24(1)? (space group C2/mwith Z= 2). The crystal structure has been refined by the Rietveld method using the structure of the related dihydrated phase as a starting model (Rp= 0.092 and RF= 0.068 for 372 reflections). The structure is characterized by octahedra [Zn(OH)6] describing a brucite-type layer, with one-quarter of the metal atoms missing, and by tetrahedra [Zn(OH)3(NH3)] located above and below the empty octahedra. The complex positive sheet has the formula [Zn3octa(OH)8Zn2tetra(NH3)2]2+and the cohesion of the structure is realized through hydrogen bonding.

The decomposition reactions of two zirconium hydroxide nitrates Zr(OH)2(NO3)2?(4+x)H2O and ?-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 (?,?,?) 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 ?-Zr(OH)2(NO3)2?(1+x)H2O include the formation of anhydrous oxide nitrate ZrO(NO3)2and anhydrous hydroxide nitrate Zr(OH)2(NO3)2, respectively.

With the explosive growth in the number of highly automated powder diffraction systems, many types of analyses which were previously considered a specialty analysis are now performed on a routine basis. Algorithms have been developed for measuring peak profiles from which crystallite sizes, residual microstrain, and X-ray crystal structure (Rietveld techniques for example) can be determined. However, these techniques require an instrumental peak profile calibration standard to correct the experimental data for instrumental broadening due to the system optics.Significant problems are encountered when laboratories try to cross-correlate or reproduce published data due to the lack of a common reference material for instrumental calibration. This is particularly distressing in microstrain and crystallite size calculations which can be dramatically affected by a poor choice of standard materials. Microstrain and crystallite size measurement are becoming increasingly important for the characterization of advanced materials and catalysts.

The new phase LaCr(NO3)6?12H2Owas synthesized from a nitric acid solution. The symmetry is trigonal with the parameters a=10.9564(4) ? and c=16.835(1) ? [V=1750.2(2) ?3, space group R-3]. The thermal decomposition, studied by temperature-dependent X-ray powder diffraction and thermogravimetry, gave successively the cubic phase LaCr(NO3)6?6H2O[a=12.301(1) ?, space group P213] and the chromate(V) LaCrO4. The reduction of LaCrO4to LaCrO3occurred at a temperature depending on the oxygen pressure in the reaction atmosphere.

Ceric caesium nitrate CeCs2(NO3)6and ceric rubidium nitrate CeRb2(NO3)6have been investigated by means of X-ray powder diffraction. Precise data collected with strictly monochromatic radiation (CuK?1) are reported. Monoclinic unit cell dimensions were found by the indexing program DICVOL91 based on the variation of parameters by successive dichotomy. The final refined parameters are: a= 13.5373(7) ?, b= 7.0787(5) ?, c= 8.1672(5) ?, ?= 90.813(5)? for the caesium compound and a= 13.0567(5) ?, b= 6.8684(2) ?, c= 8.1786(3) ?, ?= 91.436(4)? for the rubidium compound, and the indexings are characterized by the figure of merit F30equivalent to 245 (0.0033,37) and 194 (0.0040,39), respectively.

AbstractBarium titanyl oxalate tetrahydrate, Ba(TiO)(C2O4)2.4H2O, has been investigated by means of X-ray powder diffraction. Precise powder diffraction data were obtained by a conventional diffractometer with strictly monochromatic radiation. Unit cell dimensions were determined by an indexing program based on the variation of parameters by successive dichotomies. A monoclinic cell was found, a=14.044(2)?, b=13.812(2)?, c=13.382(2)?, ?=91.48(1); V=2594.9?3, which is characterized by the figures of merit M20=46.5 and F30=107(0.0056, 50). The complete powder pattern was reviewed by means of the program NBS*AIDS83 and the 81 first lines were indexed. Structural imperfections were not detected from the diffraction line widths, which are comparable to the instrumental resolution.

AbstractNeodymium ammonium hydroxynitrate, Nd(OH)2NO3.(NH4NO3)0.5.H2O, has been investigated by means of X-ray powder diffraction. Unit cell dimensions were determined by indexing programs, from diffractometer data obtained with strictly monochromatic CuK?1radiation. An I orthorhombic cell was found: a = 24.577 (4) ?, b = 7.1488 (16) ?, c = 3.8211 (9) ?. It is shown that the h 1 1 reflections present a selective line broadening.

Introduction: Phase transition has been recently observed in Cs2CdI4(Touchard, Lou?r, Auffr?dic & Lou?r, 1986). Thermal analysis has shown that the transformation occurs at 122?C. By quenching, the high temperature phase (?) can be stabilized at room temperature. In the present work we report the X-ray diffraction powder data, at room temperature, for the two phases ?- and ?-Cs2CdI4. Both phases have been indexed automatically by using powder indexing methods.

AbstractThe neodymium hydroxynitrate, Nd(OH)2(NO3).H2O, (PDF #37-1841) has been investigated by means of X-ray powder diffraction data. The unit cell dimensions were determined from diffractometer methods, using strictly monochromatized CuK?1radiation, and evaluated by indexing programs. The monoclinic cell found was a = 19.381(4)?, b = 3.884(1)?, c = 6.291(1)?, ? = 96.43(2)?.

AbstractYttrium oxalate dihydrate, Y2(C2O4)3.2H2O, has been investigated by means of X-ray powder diffraction. Unit cell dimensions were determined by an indexing program based on the variation of parameters by successive dichotomies. The diffractometer data were collected with strictly monochromatic radiation. A monoclinic cell was found: a=9.3811(8)?, b=11.6385(15)?, c=5.9726(7)?, ?=96.079(8)?, which is characterized by the figures of merit M20=87 and F30=112 (0.0065,41). A preliminary analysis of the anisotropic line broadening has revealed some microstructural properties. It is shown that line broadening is mainly due to a micro-strain effect.

AbstractCadmium hydroxide nitrate dihydrate, Cd5(OH)8(NO3)2?2H2O, and zinc hydroxide nitrate diammoniac, Zn5(OH)8(NO3)2?2NH3, have been investigated by means of X-ray powder diffraction. Their unit cell dimensions were found by an indexing program and confirmed by single crystal studies. Precise data collected with strictly monochromatic radiation are reported. The figures of merit are F30=118 (0.0071,36) for the cadmium compound and F30=53 (0.015,38) for the zinc compound. A short discussion of the unit cell parameters compared to those of a related zinc hydroxide nitrate dihydrate is presented.

AbstractPotassium calcium phosphate, KCa PO4.H2O, has been investigated by means of X-ray powder diffraction. Unit cell dimensions were determined from diffractometer data obtained with strictly monochromatized Cu K?1radiation, by indexing programs. A C-centered monoclinic cell was found: a =7.5834(9) ?, b = 8.1568(11) ?, c = 7.6541(8) ?, ?= 102.975 (9)?.