X-ray Powder Diffractograms Research Articles

Structure, exchange interactions and magnetic anisotropy of Ho2Co17−xSix compounds

The structural and magnetic characteristics of Ho2Co17−xSix (x=0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) compounds have been investigated by means of x-ray diffraction and magnetic measurements. Powder x-ray diffractograms show that all samples are single phase and have the hexagonal Th2Ni17-type or the rhombohedral Th2Zn17-type structure. The substitution of Si for Co leads to a monotonous decrease in unit cell volume v and Curie temperature TC. The compensation points are observed for the samples with x=2.5 and 3.0, and the compensation temperatures shift to higher temperatures with increasing Si content. The intersublattice-molecular-field coefficient, nHo–Co, has been determined on the basis of magnetization curves at the compensation temperature. It has been found that the Si substitution for Co has little influence on Ho–Co exchange interaction. The magnetic phase diagram has been determined from the temperature dependence of magnetization and the XRD patterns of magnetically oriented powder samples. The spin-reorientation temperatures of Ho2Co17−xSix compounds are found to decrease with Si content for x<2.5 and then increase for x>2.5, attaining a minimum value of 237 K at x=2.5.

Physicochemical Characterization of a New Crystal Form and Improvements in the Pharmaceutical Properties of the Poorly Water-Soluble Antiosteoporosis Drug 3,9-bis (N,N-Dimethylcarbamoy-loxy)- 5H-benzofuro[3,2-c]quinoline-6-one (KCA-098) by Solid Dispersion with Hydroxypropylcellulose

The present study was undertaken to improve the oral absorption of KCA-098, an antiosteoporosis drug. In this study, the form 2 of KCA-098 was used as a desirable crystal form for pharmaceutical formation among three kinds of crystal forms, 1, 2, and 3. Solid dispersions of KCA-098 with hydroxypropylcellulose (HPC) or poly(vinylpyrrolidone) (PVP) were prepared by the solvent method. The physicopharmaceutical properties of the solid dispersions were characterized by powder x-ray diffraction, FTIR spectroscopy, and differential scanning calorimetry (DSC). The powder x-ray diffractograms suggest that KCA-098 in the HPC-SL solid dispersion existed in a partial crystalline state as a new crystal form that could be produced by recrystallization from the solvent. Dissolution from the solid dispersions was markedly enhanced in comparison with that of the drug alone. The dissolution enhancement was observed to be greater for the solid dispersion with HPC-SL than for that with PVP. The KCA-098/HPC-SL (1:2) solid dispersion capsule showed a 3.5-fold increase in the initial concentration and 2.5-fold increase in initial concentration of dissolved drug after 60 min, compared with the values for a physical mixture of KCA-098 (form 2)/lactose (1:2). The in vivo absorption of the drug was investigated after oral administration of KCA-098 or its solid dispersion. The area under the plasma concentration curve of KCA-098 after oral administration of the KCA-098/HPC-SL (1:2) solid dispersion capsule was three-fold greater than that for the drug itself.

Monolayer-Protected Cluster Superlattices: Structural, Spectroscopic, Calorimetric, and Conductivity Studies

Alkanethiol-protected silver clusters of average diameter 4.0 ± 0.5 nm form single-phase superlattice solids, and their X-ray powder diffractograms have been fully indexed to single cubic unit cells. Whereas alkanethiols with five or more carbon atoms form superlattices, the corresponding cluster with four carbons yield only separated clusters. The superlattice solids can be recrystallized from nonpolar solvents. No such superlattices are seen for the corresponding gold clusters. The superlattice collapses upon heating, but the solid retains the structure even at 398 K, much above the melting point of crystalline alkanes and the corresponding self-assembled monolayer. In situ variable-temperature X-ray diffraction investigations did not show any solid-state phase transitions in the superlattice. Temperature-dependent infrared spectroscopy reveals the melting of the alkyl chain, and it is seen that the chain as a whole achieves rotational freedom prior to the collapse of the superlattice. Calorimetric inve...

Bulk structure of phototransformed C [formula omitted

We have produced phototransformed C 60 in powder form and in bulk quantities. The availability of several milligram batches allowed us to collect good quality X-ray powder diffractograms, infrared transmission spectra and differential scanning thermograms. Based on these data a disordered structural model is proposed which is built up from small closed oligomers.

Hydrogen absorption characteristics in the Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) system

The hydrogen absorption pressure-composition-isotherms of the PuNi3 type rhombohedral Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) alloys are investigated by Sievert’s apparatus, in the temperature and pressure ranges 75≤T(°C)≤150 and 0.1≤P(bar)≤25, respectively, with a view to study the dependence of hydrogen solubility and the plateau pressure on Zr content. The P-C isotherms show the presence of a single plateau region in the temperature and pressure ranges studied and it is found that the plateau pressure at any given temperature increases with increase of Zr content along with a reduction in the hydrogen capacity. The absorption of hydrogen is accompanied by a maximum of 17.4% expansion in the unit cell volume of the host material without any change in PuNi3 type structure as evidenced by the X-ray diffraction studies on the alloy– hydrides. The presence of single and two phase regions as seen in the P-C isotherms are confirmed from the powder X-ray diffractogram of the alloy–hydrides with appropriate hydrogen concentration. The powder X-ray diffractograms on the alloy–hydrides with maximum hydrogen concentration further show the absence of hydrogen induced amorphization (H1A) upon hydrogenation.

A moganite-type phase in the silica analog phosphorus oxynitride

A new polymorph of phosphorus oxynitride (PON) a silica analog has been recovered at ambient pressure by quenching after a treatment at 850 degrees C under a pressure of 2.5 GPa using cristobalite- or quartz-type phases as starting materials. This PON polymorph is a thermodynamically stable phase with its own stability field in a P-T diagram. The structure of this PON phase was refined by the Rietveld method from an X-ray powder diffractogram. It is isostructural with moganite (SiO 2 ). The discovery of this PON polymorph should stimulate a renewed interest in the occurrence of this phase in the silica system, because moganite may have a small but defined P-T stability field. These results confirm the structure of moganite as a new structure-type in AX 2 compounds.

Solid-state 13C nuclear magnetic resonance spectroscopic study on amorphous solid complexes of tolbutamide with 2-hydroxypropyl-alpha- and -beta-cyclodextrins.

The objective of the study was to obtain structural information of inclusion complexes of tolbutamide with HP-alpha- and -beta-cyclodextrins in amorphous state. The solid complexes of tolbutamide with HP-alpha- and -beta-CyDs in molar ratios of 1:1 and 1:2 (guest:host) were prepared by the spray-drying method, and their interactions were investigated by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The solid 1:1 and 1:2 tolbutamide/HP-CyD complexes showed halo pattern on the powder X-ray diffractogram and no thermal change in DSC curves, indicating they are in an amorphous state. 13C NMR signals of the butyl moiety were broader than those of the phenyl moiety in the HP-alpha-CyD solid complex, whereas the phenyl moiety showed significantly broader signals than the butyl moiety in the HP-beta-CyD solid complex. As temperature increased, signals of the phenyl carbons became markedly sharper, whereas the butyl carbons only sharpen slightly in the HP-d-CyD complex. In contrast, signals of the butyl carbons became significantly sharper whereas those of phenyl carbons only slightly changed in the HP-beta-CyD complex. Solid state 13C NMR spectroscopic studies indicated that the butyl moiety of tolbutamide is predominantly included in the HP-alpha-CyD cavity, whereas the phenyl moiety in the HP-beta-CyD cavity in amorphous complexes.

Comparison of Crystallinity of Cefditoren Pivoxil Determined by X-Ray, Differential Scanning Calorimetry and Microcalorimetry.

The heat of crystallization and heat of solution of cefditoren pivoxil of different crystallinities were determined by differential scanning calorimetry and isothermal microcalorimetry, respectively. The heat of crystallization and heat of solution of ground cefditoren pivoxil showed good linear correlation with the degree of crystallinity determined by Ruland’s method by powder X-ray diffractogram. The changes in crystallinity of amorphous cefditoren pivoxil by adsorption of alcohol vapor could be evaluated for small amounts of sample by use of heat of crystallization. Since the apparent dissolution rate of cefditoren pivoxil of various crystallinities correlated with the heat of solution, microcalorimetry was found to be useful for prediction of dissolution behavior.

Ta11Si2Se8 – Condensed Tetrakaidecahedral Ta9Si Clusters Arranged to an Open Network Structure

Ta11Si2Se8 was synthesized from a pre-reacted mixture of the elements in a sealed tantalum tube at 1570 K. Mo-doped crystals were obtained in a welded molybdenum crucible by a chemical transport reaction using TeI4 as a transport agent. The structure of Mo0.11Ta10.89(2)Si2Se8 has been determined by single crystal X-ray means [Pnnm, Z = 2, a = 1184.4(1) pm, b = 1939.4(1) pm, c = 346.48(2) pm, wR2 = 0.069]. The structure of the ternary phase was verified by means of a Rietveld profile fit of a powder X-ray diffractogram. The silicide is isotypic with Ta11Ni2Se8. The structure is composed of Si-centred, tricapped trigonal prismatic Ta9Si clusters. The tetrakaidecahedral Ta9Si clusters are fused into twin chains by sharing the Tapr atoms of facing triangulated prism faces and one out of three capping atoms Tac. Intercluster linkage of the remaining Tac atoms generates a microporous ∞3[SiTa2cTa1/2cTa6/2pr] substructure. The channels of the metal network are sheathed by three-, four-, five-, and sixfold coordinated Se atoms. Four-probe dc resistivity measurements revealed the Mo-doped phase to be a moderate metallic conductor. The bonding interactions contributing to the stability of Ta11Si2Se8 and distinctions in bonding for Ta11Si2Se8 and Ta11Ni2Se8 are analysed on the basis of semi-empirical extended Hückel calculations.

Investigation of formulation approaches to improve the dissolution of SB-210661, a poorly water soluble 5-lipoxygenase inhibitor

Several formulation approaches were used in an attempt to improve the dissolution of SB-210661. In the present study, incorporation of surfactants in formulations significantly enhanced SB-210661 dissolution in water at 37°C. The role of surfactants on dissolution enhancement was also investigated. As an alternative formulation approach, solid dispersions were also prepared using the melt and mechanical activation methods for PEG 8000 containing dispersions and using the solvent method for PVP containing dispersions. The dissolution of SB-210661 from the solid dispersions was significantly greater than that observed for the surfactant containing formulations. The physical characteristics of these solid dispersions were investigated by X-ray powder diffraction and FTIR. The X-ray powder diffractograms suggest that the PEG 8000 dispersions exist in a partially crystalline state and that the PVP dispersion exists in a totally amorphous state. The FTIR results suggest that SB-210661 does not interact with PEG 8000 but interacts with PVP through intermolecular hydrogen bonding. Following storage of solid dispersions at 25°C/60% relative humidity (RH) for 1 year, there was no significant change in the dissolution profile for the PVP dispersion, whereas the PEG dispersions showed a slowing in their dissolution rate. X-ray powder diffraction results indicated that SB-210661 was still amorphous in the PVP dispersion, and the FTIR spectrum still supported the hydrogen bonding of SB-210661 and PVP. The lack of change in the dissolution profile of the PVP dispersion may be related to the hydrogen bonding interaction causing a stabilization of SB-210661 in the higher-energy, faster dissolving amorphous state.

Fe 57 Mössbauer effect study of Nd–(Fe, Cr)–B permanent magnetic materials

The alloys Nd16Fe76−xCrxB8, with x=0, 3, 5, and 7, were prepared by induction melting technique. The x-ray powder diffractograms show that all the samples crystallized in tetragonal Nd2Fe14B phase along with NdFe4B4 as a secondary phase. The lattice parameters are found to decrease with Cr concentration. The Curie temperature, determined by the differential scanning calorimetry technique, decreases with Cr concentration at the rate of 7.4 K/at. % Cr. The Mössbauer study clearly shows that Cr has a strong preference for the j2 site; the weighted average hyperfine magnetic field decreases by 40 kOe when an Fe atom in the Nd2Fe14B formula unit is replaced by a Cr atom. Cr substitution decreases the transferred hyperfine magnetic field at the Fe sites and also the Fe-magnetic moment.

Magnetic properties of the borocarbides R 3B xC 4− x (R=Gd, Ho; x

X-ray powder diffractograms proved the occurrence of the Sc 3C 4-type of structure for Ho 3B x C 4− x for 0≤ x≤0.8, whereas the gadolinium containing compound could only be stabilized by adding 7.5 at. % boron to the sample. Ac as well as dc magnetic susceptibilities of the pure binary Ho 3C 4 exhibit an antiferromagnetic transition at a Néel temperature of T N=10 K, followed by a metamagnetic transition in external fields of H>0.1 T. The holmium borocarbides undergo ferromagnetic transitions below T C=35 K. The feature of the magnetization curves is reminiscent of a system composed of narrow domain walls. The gadolinium-borocarbide also orders ferromagnetically at a Curie temperature of T C=159 K.

Determination of the Disordered Structure of Gd2Ba2CaCu2Ti3O14 with Multiple-Edge EXAFS and Powder Diffractograms

The overall structure and the local structural features of the superconductor-related cuprate Gd2 Ba2 CaCu2 Ti3 O14 were determined by the simultaneous fitting of the data sets of five EXAFS spectra and a powder X-ray diffractogram with a single structural description. The method is particularly suitable for materials that do not exhibit perfect crystalline order.

Structure of Neohesperidin Dihydrochalcone/β-Cyclodextrin Inclusion Complex: NMR, MS, and X-ray Spectroscopic Investigation

The inclusion complex between the semisynthetic sweetener neohesperidin dihydrochalcone (1) and β-cyclodextrin (βCD) has been investigated in solution, in the gas phase and in the solid state. In aqueous solution they form a 1:1 complex having a Kbinding of 1.6 × 103 M-1 at 315 K. The nuclear Overhauser effects show that the terminal isovanillin ring of 1 is included in the hydrophobic cavity of βCD from the narrower rim of the truncated cone. The peak at m/z 1747 corresponding to the supramolecular entity [βCD + 1 + H]+ was detected by MS−FAB measurements. The fragmentation pattern of 1 is different in the presence and in the absence of βCD, suggesting that the disaccharide moiety of 1 and the external polar surface of the host are tightly associated. In the solid state evidence of the formation of the βCD/1 complex is obtained from the X-ray powder diffractograms which show diffraction peaks differing in position and intensity from those of native guest 1 and host βCD. Keywords: Neohesperidin dihydrocha...

Hydrogen absorption characteristics in Zr 0.2Ho 0.8CoFe

Hydrogen absorption studies have been carried out on the Zr 0.2Ho 0.8CoFe alloy which has the C15 cubic Laves phase structure. The data were collected in the temperature and pressure ranges 27≤ T(°C)≤150 and 0.05≤ P(bar)≤45 respectively. A maximum hydrogen concentration of 9 hydrogen atoms per formula unit at 43 bar at RT is observed. The P– C isotherms show two plateau regions which are identified as the (α+β) and (β+γ) phases. These are confirmed from the variation of thermodynamic parameters as the function of hydrogen concentration and from the powder X-ray diffractograms of the samples taken at different hydrogen concentrations. The relative partial molar enthalpy (ΔH̄ H) and entropy (ΔS̄ H) of hydrogen are found to be in the ranges - (1–8) kJ (mol H) −1 and - (13–22) J K −1 (mol H) −1, respectively. The unit cell volume expansion (Δ V/ V) up to 22% is found at the maximum hydrogen concentration at RT without a change in its crystal structure. The powder X-ray diffractogram of Zr 0.2Ho 0.8CoFeH 9 does not indicate the occurrence of hydrogen induced amorphization (HIA) unlike the case of Zr 0.2Ho 0.8Co 2H 3 even though the atomic size ratio ( R A/ R B) of Zr 0.2Ho 0.8CoFe is more than the critical value estimated for the formation of an amorphous state upon hydrogenation.

Metastability of Tialite Synthesised from Nanometric Precursors

Aluminium titanate (tialite, Al 2 TiO 5 ) is a refractory material of low thermal expansion coefficient. However, single crystals have strongly anisotropic linear expansion coefficients along their principal axes. Tialite can be readily synthesised on heating a mixture of conventional corundum and rutile powders, starting at about 1200°C; higher temperatures are required for well sintered products. Tialite crystals show severe thermal expansion anisotropy, resulting in a preferred crystalline orientation, induced by uniaxial compressing of the conventional precursor powder mixture. However, no texture was apparent in the X-ray powder diffractograms of tialite synthesised from nanometric precursors. Despite the absence of a preferred orientation in the latter case, the materials synthesised at temperatures below 1400°C proved to be very unstable, rapidly and totally decomposing into corundum and rutile at 1100°C. This transition could be repeated several times, however, the yield of tialite gradually decreased in each cycle, leaving unreacted corundum and rutile. The behaviour of tialite derived from nanocrystalline precursors is discussed in terms of thermal anisotropy, misfit volume and crystal growth of the phases involved in the process.

Reinvestgation of Tweed Microstructures in Annealed Albite

Abstract Previous TEM study of natural Amelia albite (Ab99.3An0.1Or0.6) isothermally annealed at 1073°C for various periods revealed distinct tweed microstructures from the intermediately disordered albite samples (intermediate albite), but not from both the natural sample (low albite) and the highly disordered samples (high albite).1 These tweed microstructures seemed to correlate well with the degree of peak broadening and distortion in corresponding conventional powder X-ray diffractograms. Previous XRD, synchrotron radiation and TEM studies on the annealed albite samples at 1080°C for various periods gave rise to similar results. Reinvestigation of the annealed albite samples with distinct tweed microstructures by TEM confirmed their existence in wide areas, giving two-directional streaking in the corresponding SADP’s (Fig. 1 and 2). Tweed directions are roughly perpendicular to and parallel to the trace of albite twin plane, {010}, as shown in Fig. 3. This tweed microstructure is apparently unaffected by the twinning and probably formed after it.

Alluaudite-like Structure of the Complex Arsenate NaCaCdMg2(AsO4)3

The existence of a continuous series of solid solutions NaCaCdMg2[(PO4)1−x(AsO4)x]3(0≤x≤1) suggests an alluaudite-like structure of the arsenate NaCaCdMg2(AsO4)3. This is definitely confirmed by a Rietveld analysis of its X-ray powder diffractogram. The crystal cell is monoclinic, space groupC2/c, witha=12.2363(1),b=12.9869(1),c=6.7742(1)Å,β=113.7985(3)°. The Mg2+cations are essentially located on theM(2) sites of the alluaudite structure, but the distribution of the Na+, Ca2+, and Cd2+cations over theM(1),X(1), andX(2) sites is more or less disordered. The existence of a partial disorder in the cation distribution is supported by some diffuseness of the Raman and IR spectra.

Binary System of (R)- and (S)-Nitrendipine—Polymorphism and Structure

Three monotropically related modifications of (RS)-nitrendipine (RS-NTD) were investigated. With the aid of the optical antipodes of NTD, it was possible to construct a binary phase diagram, from which it is obvious that the thermodynamically stable mod. I of RS-NTD (mp 156–158.5 °C, heat of fusion 41.1±0.2kJ mol−1) is a racemic compound, while mod. II (mp 130–134 °C, heat of fusion 29.4kJ mol−1) and mod. III (mp 124–126 °C, heat of fusion 27.2kJ mol−1) occur as conglomerates of different modifications of R- and S-NTD. The eutectic points (calculated) are at 150 °C and at 19% and 81% molar fraction of an enantiomer, respectively. Two modifications of the enantiomers are characterized (En-mod. I, thermodynamically stable form, mp 156–158 °C, heat of fusion 34.5±1.3kJ mol−1 and En-mod. III, mp 121 °C), whereas a third modification (En-mod. II) must be hypothesized pursuant to the phase diagram (mp ca. 152 °C). IR spectra, DSC curves, and X-ray powder diffractograms of the different phases are described. The crystal structure of the enantiomer En-mod. I is reported (monoclinic, P21, density 1.346g cm−3) and compared with the X-ray structure of the racemic compound (monoclinic, P21/c, density 1.356g cm−3). A comparison with similar studies on nimodipine has been made to emphasize the parallels to a substance of this chemical group.

Synthesis, characterization and structural studies of mono- and polynuclear complexes of zinc(II) with 1,10-phenanthroline, 2,2′-bipyridine and 4,4′-bipyridine

Three complexes of the formula [Zn(2,2′-biny)(CCl 3CO 2) 2(H 2O)] ( 1). [Zn (1,10-phen) (CCl 3CO 2) 2(H 2O)] ( 1a) and [Zn(μ-4,4′-bipy)(4-4′-bipy) 2(CCl 3CO 2) 2(H 2O) 4] n ( 2) have been synthesized and characterized by elemental analysis, IR spectra, thermal analysis and single-crystal X-ray diffraction for 1 and 2 and X-ray powder pattern for 1a. The metal coordination in complex 1 is distorted trigonal bipyramidal with N(1), O(2) and O(5) defining the basal plane, O(3) and N(2) being in apical positions. The X-ray crystal structure of 2 reveals that the local coordination round the Zn II ion is a distorted octahedron, in which Zn(H 2O) 4 coordination planes are bridged by 4,4′-bipyridine to form an infinite chain structure. Two 4,4′-bipyridine molecules and two trichloroacetate anions exist in the lattice linked by intermolecular hydrogen bonds to coordinated water molecule. Complexes 1 and 1a have a similar pattern of bonding and showed identical TGA curve and almost similar X-ray powder diffractograms.