J. M. Amigo

XRD microstructural analysis of mullites obtained from kaolinite–alumina mixtures

Abstract A microstructural study of mullite obtained by the reaction sintering of kaolinite–α–alumina mixtures in the range 1150–1700°C has been performed by using X-ray line profile analyses together with scanning and transmission electron microscopy equipped with microanalysis by energy dispersion (SEM-EDS, TEM-AEM). Two kinds of morphology corresponding to primary (elongated grains) and secondary (equiaxed grains) mullite have been observed. A bimodal crystallite size distribution has been detected through XRD microstructural analysis from 1300°C. The results obtained by this method are compared with SEM/TEM data.

Quantitative X-ray diffraction phase analysis of coarse airborne particulate collected by cascade impactor sampling

Mineralogical composition of Castellon (Spanish Mediterranean coast) atmospheric aerosol was studied by X-ray diffraction by sampling with a cascade impactor without filters. Quantitative phase analysis of natural phases present in the atmospheric coarse aerosol was performed using a modified version of the computer program MENGE, that uses the standardless X-ray method developed by Rius for the quantitative analysis of multiphase mixtures, adapted for PC running. Presence of quartz, calcite and gypsum was identified in the atmospheric aerosol and we have quantified their amounts using the standardless method.

Crystallinity of Lower Cretaceous kaolinites of Teruel (Spain)

Abstract The crystallinity criteria based on X-ray diffraction powder data of unoriented samples proposed to date for kaolinite, are usually difficult to apply to polimineralic samples because of overlapping peaks. The aim of this work is to avoid this problem by using X-ray diffraction data of oriented samples to measure crystallinity. Fast X-ray diffraction patterns registering the 001 and 002 peaks and the 02,11 bidimensional band have been performed and the crystallinity has been obtained by comparing the fast patterns with classifications based on the appearance of X-ray diffraction patterns, which are related to the definition of the peaks in the 02,11 band and to the width and height of the 001 and 002 peaks (Thorez, 1976). The 001 and 002 reflections have also been studied in X-ray diffraction patterns of oriented powder aggregates with a slow goniometer speed; the obtained data have been used to calculate the crystallite size in the [001] direction by the methods of Williamson and Hall (1953) and Warren and Averbach (1950), and the results of both methods have been compared. The extent of the hydrazine intercalation has been tested by the Tchoubar et al. (1982) index. The particle size has been observed by TEM. The methods of Williamson and Hall and Warren and Averbach used for measuring crystallite size in the [001] direction offer consistent results and with a good correlation. These results have been compared with evaluations of crystallinity based on the appearance of the X-ray diffraction pattern of the unoriented sample and with the corresponding values of the Tchoubar et al. (1982) index. The 001 and 002 reflections are affected by the general diminution of crystallinity as shown in powder patterns of the unoriented sample, and thus a line broadening is observed. The hydrazine intercalation capacity seems to be related to the crystallite size in the [001] direction (a general tendency to the greater Tchoubar rate the lower size can be observed) but not with the particle size and morphology of the (001) plates observed by TEM.

X-ray powder diffraction phase analysis and thermomechanical properties of silica and alumina porcelains

Chemical and mineralogical characterization, using the Rietveld method, of some silica and alumina rich porcelains and its relationship with thermomechanical properties have been studied in this work. X-ray powder diffraction analysis allows to differ clearly between silica and alumina porcelains. X-ray study shows that both porcelains have a content of vitreous phase. This vitreous phase is higher in the silica than in the alumina porcelain. Dilatometric studies combined with powder diffraction methods shows a strong relationship between silica content and a lower expansion coefficients and between alumina content and a higher crash resistance. Lower contents in vitreous phase in porcelain yields to higher thermal expansion coefficients.

Synthesis and spectral studies on metal complexes with the neutral O,N,O-tridentate Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone: Crystal structure of a bidimensionally hydrogen-bonded perchlorate copper(II) complex

Abstract From the reaction between different Co(II), Cu(II), Zn(II) and Pd(II) salts and the Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone (H 2 BEZDO), in ethanol and acetone media, five complexes with M/L stoichiometry 1/1, containing the neutral organic ligand, have been obtained. These compounds have been studied by IR, 13 C and 1 H-NMR, UV-VIS-NIR and EPR spectroscopies and magnetic measurements. A single crystal X-ray diffraction study has been carried out on the compound [Cu(ClO 4 )(H 2 BEZDO)(H 2 O)]ClO 4 . The structure consists of mononuclear cations [Cu(ClO 4 )(H 2 BEZDO)(H 2 O)] + and uncoordinated perchlorate anions. The coordination environment around the Cu(II) may be described as a square-based pyramid in which the Schiff base acts as tridentate ligand through the O(4), N(51) and O(52) atoms, making two five- and six-membered chelate rings. The coordination sphere is completed with the oxygen atom of the water molecule and an oxygen atom of a weakly coordinated perchlorate group occupying the apical position of the polyhedron. Both complex units and uncoordinated perchlorate anions are extensively hydrogen-bonded, forming bidimensional sheets.

Phase Transitions in Tris(3,5-dimethylpyrazol-1-yl)methane. The Structure of the High-Temperature Phase from X-ray Powder Diffraction

The crystal structure of the sublimated form (m.p. = 424 K) of tris(3,5-dimethylpyrazol-l-yl)methane has been solved by a Patterson search method from laboratory X-ray powder diffraction data. Crystal data: trigonal symmetry with the unit-cell parameters a = 16.152 (1) and c = 5.353 (1) A, space group P3, C16H22N6, Z = 3, 293 K. After indexing the powder pattern by two methods, the unit-cell parameters found were refined by a least-squares technique. A whole pattern-fitting program was used to extract the integrated intensities. The structure was solved taking a related compound as a search model and the final Rietveld refinement converged to Rwp = 0.077 and Rp = 0.059. This study is one of the first examples of Patterson search structure determination from an hemihedral space group using powder data. The complexity of the structural determination is increased by the presence of three molecules in the asymmetric unit.

Copper(II) complexes with the N,N,O-tridentate ligand 6-amino-5-formyl- 1,3-dimethyluracilato-(N6)-benzoylhydrazone: synthesis, spectral and XRD studies

Abstract From reactions between different Cu(II) salts and the Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone (H 2 BEZDO) in alcohol, six new copper complexes with simplified formulas [Cu(HBEZDO)(H 2 O)(MeOH)]NO 3 ( 1 ), [CuCl(HBEZDO)(DMF)] ( 2 ), [CuBr(HBEZDO)]·2H 2 O ( 3 ), CuBr(HBEZDO) ( 4 ), Cu(ClO 4 )(HBEZDO)·H 2 O ( 5 ), and Cu(SO 4 ) 1/2 (HBEZDO)·1 1 2 H 2 O ( 6 ) were isolated. The structures of compounds 1 , 2 and 3 have been established by means of XRD diffraction methods. In the three compounds, the Schiff base acts as a tridentate monodeprotonated ligand through the N(6), N(51) and O(52) atoms, making two five- and six-membered chelate rings. In the structure of 1 and 2 , the solvent molecules are coordinated giving square-based pyramidal environments, with the basal plane completed by a MeOH ( 1 ) or Cl ( 2 ) and the apical positions occupied by the oxygen atom of a water ( 1 ) or a DMF molecule ( 2 ). The molecular unit of the complex [CuBr(HBEZDO)]·2H 2 O ( 3 ) is defined by a square-plane containing the three donor atoms of the organic ligand and a bromide ligand (Cu–Br 2.384 A), but there is a stronger tetragonally elongated pyramidal geometry around the metal, the apical position of the polyhedron being occupied by a weakly bound-to-copper bromine atom (3.086 A) of a neighbouring molecule. This fact gives the appearance of an apparent dimer with very asymmetric bromine bridges, in which there are no exchange interactions between metal centres. Also, infrared, magnetic and EPR data of the isolated complexes are reported.

Quantitative Phase Analysis of Mixtures of Three Components using Rietveld and Rius Standardless Methods. Comparative Results

Eight samples, supplied by the Commission on Powder Diffraction of the International Union of Crystallography, through the Round Robin on quantitative phase analysis, were analized using standardless methods. Samples were mixtures of corundum, zincite and fluorite in different ratios. The Rietveld method, using the DBW 3.2 and FULLPROF software, and the Rius method, using MENGE-PC software, were used. Results obtained agree well with the real composition supplied (a posteriori) by the IUCr.

A tangent formula derived from Patterson-function arguments. VII. Solution of inorganic structures from powder data with accidental overlap

Accidental overlap constitutes one of the principal limitations for the solution of crystal structures from powder diffraction data, since it reduces the number of available intensities for direct-methods application. In this work, the field of application of the direct-methods sum function is extended to cope with powder patterns with relatively large amounts of accidental overlap. This is achieved by refining not only the phases of the structure factors but also the estimated intensities of the severely overlapped peaks during the structure solution process. This procedure has been specifically devised for inorganic compounds with uncertain cell contents and with probable severe atomic disorder, a situation often found when studying complex minerals with limited crystallinity. It has been successfully applied to the solution of the previously unknown crystal structure of the mineral tinticite. Finally, an estimation of the smallest ratio (number of observations to number of variables) for the procedure to be successful is given.

A tangent formula derived from Patterson-function arguments. II. Practical tests with single-crystal intensity data

A series of test calculations of the tangent formula derived from Patterson-function arguments [Rius (1993). Acta Cryst. A49, 406–409] using single-crystal intensity data is presented. This new tangent formula has been compared with the results reported [Sheldrick (1990). Acta Cryst. A46, 467–473] for (a) the tangent formula incorporating the most reliable negative quartets and (b) its extension to the phase-annealing method. The success rate of the new tangent formula is an order of magnitude higher than that of (a), is better than that of (b) when the origin can float in at least one direction, and is similar to that of (b) for other space groups.