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Powder pattern indexing can still be a challenge, despite the great recent advances in theoretical approaches, computer speed and experimental devices. More plausible unit cells, belonging to different crystal systems, are frequently found by the indexing programs, and recognition of the correct one may not be trivial. The task is, however, of extreme importance: in case of failure a lot of effort and computing time may be wasted. The classical figures of merit for estimating the unit-cell reliability {i.e.M20[de Wolff (1968).J. Appl. Cryst.1, 108–113] andFN[Smith & Snyder (1979).J. Appl. Cryst.12, 60–65]} sometimes fail. For this reason, a new figure of merit has been introduced inN-TREOR09, the updated version of the indexing packageN-TREOR[Altomare, Giacovazzo, Guagliardi, Moliterni, Rizzi & Werner (2000).J. Appl. Cryst.33, 1180–1186], combining the information supplied byM20with additional parameters such as the number of unindexed lines, the degree of overlap in the pattern (the so-called number of statistically independent observations), the symmetry deriving from the automatic evaluation of the extinction group, and the agreement between the calculated and observed profiles. The use of the new parameters requires a dramatic modification of the procedures used worldwide: in the approach presented here, extinction symbol and unit-cell determination are simultaneously estimated.N-TREOR09benefits also from an improved indexing procedure in the triclinic system and has been integrated intoEXPO2009, the updated version ofEXPO2004[Altomare, Caliandro, Camalli, Cuocci, Giacovazzo, Moliterni & Rizzi (2004).J. Appl. Cryst.37, 1025–1028]. The application of the new procedure to a large set of test structures is described.

A high-pressure phase of vanadium pentoxide, denoted β-V2O5, has been prepared at P = 6.0 GPa and T = 1073 K. The crystal structure of β-V2O5 has been studied by X-ray and neutron powder diffraction, and high-resolution transmission electron microscopy. The V atoms are six-coordinated within distorted VO6 octahedra. The structure is built up of quadruple units of edge-sharing VO6 octahedra linked by sharing edges along [010] and mutually connected by sharing corners along [001]. This arrangement forms layers of V4O10 composition in planes parallel to (100). The layers are mutually held together by weak forces. β-V2O5 is metastable and transforms to α-V2O5 at 643–653 K under ambient pressure. Structural relationships between β- and α-V2O5, and between β-V2O5 and B-Ta2O5-type structures are discussed. The high-pressure β-V2O5 layer structure can be considered as the parent of a new series of vanadium oxide bronzes with cations intercalated between the layers.

Star polymers consisting of poly(e-caprolactone), PCL, attached to third generation dendrimer, hyperbranched and dendron cores have been studied by differential scanning calorimetry and wide-angle ...

The superstructure of potassium titanate, KTiO2(OH), prepared by hydrothermal synthesis has been determined from synchrotron powder diffraction data. It is shown that the unit cell of the superstructure is rhombohedral: a = 11.13848 Å, α = 52.7336°. The structure has been determined and refined in space group R3̅c to R F = 0.074. The distribution of hydrogen atoms as hydroxy groups can be explained from the crystal structure described by the supercell.

The crystal structure of Nd10W22O81, neodymium tungstate, has been determined using a combination of high-resolution transmission electron microscopy and X-ray powder diffraction methods. The unit-cell dimensions determined from X-ray data are a = 3.8613 (1), b = 35.9431 (1), c = 21.8900 (1) Å, V = 3038.05 Å3, Z = 2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO3-type fragments consisting of three octahedra, thus forming W9O32 units. These units form `pillars' along a. These `pillars' are joined by pairs of tilted octahedra (W2O11 groups) to form corrugated layers perpendicular to b. The Nd atoms are located in the space between these layers and form the only link between them. Interstitial O atoms are located between two of the Nd atoms. The formula Nd10W22O81 can thus be alternatively given as Nd5W11O39 + x (x ≃ 1.5), where x represents the interstitial O atoms. Nd10W22O81 is a new type of PC structure.

Indexing of a powder diffraction pattern is still a critical point in procedures aiming at solving crystal structures from powder data. New code has been associated to the programTREOR90 in order to define an efficient peak search procedure, to modify the crystallographic decisions coded intoTREOR90 to make it more exhaustive, to refine the selected unit cell automatically, and to make the entire procedure user friendly,viaa graphical interface. The new program, calledN-TREOR, has been integrated into the packageEXPOto create a suite of programs able to provide a structural model from the analysis of the experimental pattern.N-TREORis also available as a stand-alone program.

A sample of Ta2O5, ditantalum pentaoxide, heat-treated in a `toroid'-type high-pressure chamber at P = 8 GPa and T = 1470 K, was studied by X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM). Two high-pressure modifications of Ta2O5, isostructural with B-Nb2O5 and Z-Nb2O5, were identified from the X-ray powder pattern. Both structures were refined by the Rietveld method from the X-ray diffraction data: B-Ta2O5, a = 12.7853 (4), b = 4.8537 (1), c = 5.5276 (2) Å, β = 104.264 (2)°, V = 332.45 Å3, Z = 4, space group C2/c; Z-Ta2O5, a = 5.2252 (1), b = 4.6991 (1), c = 5.8534 (1) Å, β = 108.200 (2)°, V = 136.53 Å3, Z = 2, space group C2. The Z-Ta2O5 modification is new. The Ta atoms are six-coordinated in B-Ta2O5 and seven-coordinated in Z-Ta2O5. The two structures are closely related, which makes an intergrowth and a transformation between them possible. An idealized model of the intergrowth structure has been given. The HRTEM study showed defect-rich B-Ta2O5 crystals, which could be interpreted as an intergrowth between the B-Ta2O5 and Z-Ta2O5 phases.

The transformation of H-Nb{sub 2}O{sub 5} has been studied by using a toroid-type high-pressure chamber at pressures of 5.0 and 8.0 GPa in the temperature region 800--1400 C. A mixture of B-Nb{sub 2}O{sub 5} and a new modification of niobium pentoxide (denoted Z-Nb{sub 2}O{sub 5}) with seven-coordinated niobium was found in the samples after treatment at P = 8.0 GPa, T = 800--1100 C for 1--10 min. The structure was determined and refined by the Rietveld method from X-ray powder diffraction data. The thermogravimetric analysis showed no reduction of the sample.

The crystallization and melting behaviour and the morphology of fractions of poly(propylene-stat-ethylene) with 2.7–11.0 mol% ethylene were studied by differential scanning calorimetry, wide-angle X-ray scattering, polarized light microscopy and transmission electron microscopy, after etching with permanganic acid. The inclusion of ethylene co-repeating units in isotactic polypropylene (0–11.0 mol% ethylene) caused approximately linear decreases in kinetic and equilibrium melting temperatures and in the glass transition temperature with increasing ethylene content. X-ray scattering showed that the content of the γ form increased with increasing ethylene content, increasing crystallization temperature and decreasing cooling rate from the molten state. It was shown for one of the copolymers (8.7 mol% ethylene) that during heating approximately 50% of the γ form was converted to the α form before the final melting of the sample. The rest of the γ crystals melted without transformation to the α form. The multimodality of the crystal melting above the crystallization temperature in the polymers with a more uniform crystal structure was caused by recrystallization during heating, whereas polymers with appreciable contents of both α and γ forms exhibited multimodal melting at all the heating rates adopted. The size of the low temperature melting peak as assessed at a heating rate of 40 K min−1 was approximately proportional to the initial content of the γ form. By comparison with the spherulitic structure of homopolymers, that of the copolymers was coarser with internal and peripheral pockets of molten material during spherulite growth. The crystal lamellae exhibited more curvature in the copolymer samples than in the homopolymer.

The temperature dependence of the Zn2+/Mg2+ cation ordering among five- and six-coordinated metal sites in γ-(Zn1−x Mg x )3(PO4)2 solid solutions has been studied by X-ray powder diffraction methods. The structures of polycrystalline samples (P21/n; Z = 2) prepared at and quenched from different temperatures have been refined with the Rietveld technique. The structure factor R-values are in the range 0.04–0.05. It is shown that ordering with zinc preferably at the five-coordinated site is enhanced with temperature. Approximate thermodynamic data for the exchange reaction have been derived.

A high-pressure modification of tungsten dioxide (hp-WO2) was synthesized at 80 kbar and 1120 K. The structure was determined from X-ray powder diffraction data: hp-WO2, M = 215.85, space group Pnma, a = 9.7164(3) Å, b = 8.4380(3) Å, c = 4.7564(2) Å, Z = 12, D x = 11.03 g cm−3, Rwp = 0.12 and RB = 0.078 from Rietveld refinement. Although the heavy atom structure may be reasonably well described in space group Cmcm, the total structure can only be described in Pnma. The important information contained in non observable and very weak reflections is discussed. In the hp-WO2, modification the W atoms occupy half of the octahedral interstices of an hcp arrangement of oxygen atoms. It can be described as a distorted rutile structure which is twinned at the unit cell level. An essential feature is that groups of three edge-sharing WO6 octahedra are formed at twin planes. The relation between the ambient-pressure (distorted rutile type) and the high pressure modifications is discussed.

The correlation between structure and thermal properties of halogeno methylpyridine cobalt(II) is described. The ternary mixed tetrakis-derivatives and the tetrahedral bis-complexes of cobalt(II) chlorides and bromides formed with picolines are structurally very similar to the cadmium(II) and nickel(II) analogues, the iodides are somewhat different, however. On the basis of the characteristic correlation between the densities calculated from powder diffraction data and the molecular weights, the densities of a few thermal intermediates, which have not yet been prepared, are predicted. The square bipyramidal structure of dibromotetrakis(3-methylpyridine)cobalt(II) is described, and the deformation of the octahedra is discussed in detail. Structural study was extended by molecular mechanics (MM+ and MMX) and molecular orbital (SINDO1) calculations.

Two new high-pressure tungsten oxides, prepared at P=50×10 5 kPa and T=1773 K, have been investigated by high-resolution electron microscopy. The formula, W 3 O 8 for both phases, and the structures were deduced from the micrographs and verified by simulated image calculations. The phases are both orthorhombic, with the following unit-cell dimensions determined from X-ray powder patterns: W 3 O 8 (I), a=6.386 (9), b=10.43 (5), c=3.80 (1) A, V=253.1 A 3 , Z=2, space group C222; W 3 O 8 (II), a=10.35 (5), b=13.99 (5), c=3.78 (1) A, V= 547.3 A 3 , Z=4, space group Pbam

In this work orientation effects in rubber materials have been studied by X-ray scattering measurements. The rubber materials were made by injection moulding and were anisotropic as judged from mechanical and swelling measurements. In X-ray diffractograms it was possible to detect preferred orientation of both rubber molecules and zinc oxide. It may also be concluded that zinc oxide acts as an indicator of macromolecular orientation in an anisotropic rubber material.

Synthese d'un nouveau type d'oxyde de tungstene a partir d'un melange de W et WO 3 par une methode de frittage en phase solide dans des conditions de haute pression. Etude de la structure de ce compose par diffraction electronique et microscopie electronique en transmission a haute resolution. Cristallisation dans Cmm2 avec a=17.16, b=10.32, c=3.78A, Z=44.

Four (Zn 1− x Mg x ) 3 (PO 4 ) 2 solid solutions have been prepared at 800°C and the crystal structures ( P2 1 n; Z = 2 ) refined with the Rietveld technique on the basis of X-ray powder diffractometer data. The structure factor R -values are in the region 0.03–0.08 for 274 independent reflections. The Zn +2/ Mg +2 cation distribution is ordered with zinc preferably at the five-coordinated and magnesium at the six-coordinated metal sites. The cation distribution coefficient K D is around 20 irrespective of the composition.

Stereospecific multistep synthesis and resolution of 6,7-dimethoxy-4- phenyl-1,2,3,4-tetrahydroisoquinoline (3) has been achieved from its racemic base. The absolute configurations of the optical antipodes converted into their hydrochloride salt forms have been determined by X-ray diffractometric analysis, thus permitting assignment of the antipodes as the (+)-(4R)-3 and (-)-(4S)-3 enantiomers. The crystal structures of the two enantiomers are related as mirror images and only the (4R)-3.HCl form has been fully determined by three-dimensional X-ray diffraction. In the solid state, the carbon atoms of the two methoxy groups deviate slightly from the benzene-ring plane and the chirally oriented phenyl substituent is almost perpendicularly tilted out of conjugation with the isoquinoline system. Examination of the enantiomers in several biochemical tests for 5-HT, NE and DA uptake inhibition-activity revealed an exclusive preference for the (4S)-enantiomer. These results are in accord with previous suggestions that the S-configurational state of the 4-phenyl substituent is important for biological activity.

Rietveld refinements have been used to determine the cation distributions in three (Mg,Co) orthovanadates (X-ray data) and in Co 1.5 Ni 1.5 (VO 4 ) 2 (neutron powder diffraction data). The compounds crystallize in the orthorhombic space group Cmca(Z=4), with two distinct octahedral metal sites having point symmetries 2/m and 2. The refinements show that in all solid solutions the cation distributions are almost random, with a slight preference of Co 2+ for the most symmetric site.

Preparation et etude des trois solutions solides Ni 2 Mg(VO 4 ) 2 , Ni 1,5 Mg 1,5 (VO 4 ) 2 et NiMg 2 (VO 4 ) 2 . Ces composes cristallisent dans Cmca avec Z=4. La distribution Ni 2+ /Mg 2+ s'effectue presque au hasard, mais le nickel presente une legere preference pour le site octaedrique le moins symetrique, mais le plus petit. Comparaison avec la repartition dans la structure divine et trois autres structures

The phase transformation of redβ-Cu2HgI4to the blackα-phase at 67°C has been studied by X-ray powder diffraction. It is suggested that copper and iodine occupy the same tetrahedral positions in theα- andβ-phases, whereas mercury is statistically distributed over two crystallographic positions in theα-phase. Both phases may be described in space groupI[unk]2m. The phase transition has been studied by X-ray powder diffraction at elevated temperatures and disintegration of theα-phase may occasionally be found. The structure of theα-phase at 85°C was determined and refined by Rietveld full-profile technique to a BraggR-factor = 0.064.

The structure of TlCu7Se4 (synthetic crookesite) has been refined from X-ray powder data using the Rietveld technique. The compound is isostructural with NH4Cu7S4 and TlCu7S4, although successful r ...

Cristallisation dans C2/c avec a=11,942, b=8,370, c=9,936 A, β=118,77 o , Z=4; affinement jusqu'a R=0,046. La structure consiste en deux types d'octaedres FeO 6 (ayant une distance moyenne Fe-O de 2,13 A) et en anions P 4 O 12 4− avec une forme cyclique

The phase Bi23Cu3Ti4O12 has been synthesized and studied with electron and powder diffraction. The crystallographic study was performed by full-profile analysis of powder diffraction data obtained with a STADI/P diffractometer, using the mode of symmetric transmission geometry. The structure is of the perovskite related CaCu3Mn4O12 type. The title compound crystallizes in the cubic space group Im3 with a = 7.4175(3) A and z = 2. Bismuth occupies the icosahedral A-sites of ideal perovskite. The eight nearest oxygen neighbours of copper form two perpendicular rectangles of different size, and titanium occupies the B-sites of ideal perovskite.

A small but distinct shift of 0.2% in the unit cell axis of BaNbO 3 has been observed between samples having gross compositions on different sides of the BaNbO 3 -Ba 2 Nb 5 O 9 binary line in the Ba-Nb-O system. To investigate if this shift was due to a variation of the Ba-occupancy, profile refinements using the Rietveld technique were made. The outcome of these refinements are discussed.

A new type of tungsten oxide has been synthesized from a mixture of W and WO 3 by a solid-phase sintering method under high-pressure conditions. The crystal structure of the new oxide was investigated by HRTEM, selected-area electron diffraction and X-ray powder diffraction. The structure belongs to space group Pbam or P2 1 2 1 2 and has the following unit-cell parameters: a=21.431 (9), b=17.766 (7), c=3.783 (2) A, V=1440 A 3 , Z=32, D x =8.33 g cm -3 . The structural model and W-cation positions were determined by HRTEM and image processing

The crystal structure of Zn(OH)(NO3) · H2O has been studied by X-ray diffraction methods using fibrous microcrystals and powder. The cell dimensions are a = 17.951 A, b = 3.2600 A, c = 14.272 A, and β = 114.91°. The space group is P2 1 c . The structure has been refined by the Rietveld full-profile technique. The results obtained from different data sets and the corresponding discrepancy indicators are compared. The structural chemistry of the compound is discussed and an interpretation of its topotactic transformation into Zn3(OH)4(NO3)2 is presented.

The compound Mg2SiNi3 was synthesized. The hexagonal unit cell dimensions are a = 5.0044(2) A and c = 11.0894(6) A ; M20 = 333. The structure was determined and refined from Guinier-Hagg X-ray powder diffraction intensities in the space group R 3 2 m . The R value obtained was 0.073.

The extent of structural variability of boehmite has been studied by the comparison of the structure parameters of a synthetic and a natural mineral sample. Profile-fitting refinement based on Guinier-Hagg type powder data was used to determine the actual structures. It is also concluded that the small structural differences found do not interfere with the established practice of taking boehmite as reference in X-ray diffractometric quantitative phase analysis of minerals.

The two phases Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]GeO4 have been prepared by solid state reactions. X-ray powder diffraction data have been used to refine the crystal structures by the Rietveld full-profile technique. Both compounds have cristobalite-related structures. The refinements did not converge fully and constrains on the positional parameters (pairwise linking) had to be introduced. The RF and RWP values obtained for Na1.8[Ga0.2Zn0.8]SiO4 were 0.104 and 0.191 and for Na1.8[Ga0.2Zn0.8]GeO4, 0.078 and 0.159 respectively.

Etude des modeles pour la dissolution de CaF 2 dans NaF fondu. Il semble que Ca 2+ ne soit pas l'espece calcique dominante. Formation de CaF 3 − et CaF +

Three compositions of solid solutions Li1−xTa3O8−xFx (x = 0) 0.25 and 0.5) have been studied by full-profile analysis of microdensitometer-measured Guinier-Hagg powder diffraction data. From sequential changes in disorder and interatomic distances within this series, the preferred lithium position is proposed to be approximately (0.11, 12, 0.03). The results obtained for the high temperature modification of LiTa3O8 by A.G. Nord and J.O. Thomas from X-ray single crystal and neutron powder diffraction data [Nord, A.G. and Thomas, J.O., Acta Chem. Scand., in press] are discussed in view of the present investigation.