Powder Diffraction Investigations Research Articles

Neutron and X-ray powder diffraction investigation of LaMnO3

Neutron and X-ray powder diffraction investigation of LaMnO₃

Powder diffraction investigations of a new class of rare earth aluminium hydrides

Powder diffraction investigations of a new class of rare earth aluminium hydrides

Pressure-induced over-hydration and water ordering in gismondine: A synchrotron powder diffraction study

This paper reports the results of an in situ HP synchrotron X-ray powder diffraction investigation on the natural zeolite gismondine (ideal chemical formula Ca 4 Al 8 Si 8 O 32 ·16H 2 O, space group P 2 1 / c ). The study was performed from P amb to 7.9 GPa, and upon decompression, using methanol:ethanol:water (16:3:1) mixture (m.e.w.) as a nominally penetrating hydrostatic P -transmitting medium. No complete X-ray amorphization is observed up to the highest investigated pressure, and the original unit-cell parameters are almost completely recovered upon decompression. From 0.6 GPa, the water content is slightly higher than at ambient pressure, as a result of a moderate over-hydration. Moreover, at about 2 GPa, a significant water molecule system re-arrangement occurs, characterized by an ordering of part of the water molecules from four partially occupied sites to only two fully occupied ones. The over-hydration, but not the water ordering, is substantially irreversible upon pressure release. The Rietveld structural refinements of the powder patterns converged successfully up to 2.8 GPa; above this pressure, a phase transition to triclinic symmetry was observed and only the unit-cell parameters were refined. The comparison of the overall cell volume reductions and of the bulk modula of gismondine compressed between P amb and 7.9 GPa in m.e.w. and in silicone oil, reveals that this is the unique zeolite with a higher compressibility in penetrating vs. non-penetrating P -transmitting media. This is ascribed to the re-organization of the water molecule system upon compression in m.e.w., which leaves a larger free volume inside the pores with respect to the phase compressed in silicone oil.

Magnetic properties of Bi0.5Sr0.5FexMn1−xO3 (⩽x⩽0.7)

Fe-substituted manganites Bi0.5Sr0.5FexMn1−xO3 (0⩽x⩽1.0) were synthesized by a solid-state reaction. X-ray powder diffraction and neutron diffraction investigations performed at room temperature show that the crystal structure is orthorhombic for x⩽ 0.3 and cubic for x>0.4. The unit cell volume increases with x. Magnetic properties were studied between 5 and 1000K in a magnetic field up to 16kOe for the compounds with x⩽0.7. A charge/orbital ordering feature was only observed in magnetization curves for the compound with no Fe. The magnetic state of the compounds with different Fe contents changes from paramagnetic to weak antiferromagnetic below the temperature TN varying in the range of 115–155K. Unusual thermomagnetic behavior in the paramagnetic region was observed, which could be related to a coexistence of antiferromagnetic and ferromagnetic fluctuations far above TN. The typical thermomagnetic zero field cooled/field cooled hysteresis below about 40K can be related to the formation of small ferromagnetic clusters below that temperature. The conductivity of the compounds, measured between 90 and 600K, is of the semiconducting type, and no magnetoresistant effect was observed for any of them in a field of 7kOe.

Phase Equilibria in the Ternary Nb-Cr-Al System and Site Occupation in the Hexagonal C14 Laves Phase Nb(AlxCr1-x)2

AbstractThe ternary Nb-Cr-Al phase diagram exhibits extended phase fields of the cubic C15 and the hexagonal C14 Laves phases Nb(AlxCr1-x)2. A number of Nb-Cr-Al alloys were prepared by levitation melting and annealed at temperatures between 1150 and 1450 °C for up to 1500 h. Isothermal sections of the ternary Nb-Cr-Al phase diagram at 1150, 1300 and 1450 °C were obtained from electron probe microanalysis, X-ray powder diffraction and metallographic investigations in order to study the effect of Al on the stability and structure of the Laves phases. The C14 Laves phase in the Nb-Cr-Al system can dissolve up to 45 at.% Al by substituting Cr with Al on the two different crystallographic B-sites 2a and 6h of the C14 AB2 unit cell. The site occupations of the Al and Cr atoms on these two B-sites were determined by Rietveld analysis using the program FullProf. The experimental site occupation factors were compared to site occupation factors computed by a statistical mechanics approach based on first-principles electronic structure calculations. The experimental as well as the calculated site occupation factors indicate a preferred occupation of the 2a site by Al.

X-ray powder diffraction investigation of new oxynitride precursors: rare earth oxide compounds of fluorite- and sheelite-type structures in the Yb-(Zr,W)-O system

Nanocrystallized oxide precursors of colored (oxy)nitrides related to the system Yb-(Zr-W)-O have been successfully prepared using achimie douceprocess—the amorphous citrate route. The process involves first a formation of fine and homogeneous powdered solids obtained by calcination at 600 °C, a temperature much lower than that of the conventional solid-state method. At this stage, the X-ray diffraction patterns exhibit large line broadening effects. Finally, two well-crystallized and pure quaternary oxides have been readily obtained by heating and under annealing conditions at 850 and 900 °C for 12 h. For one of the patterns, all the X-ray diffraction lines can be easily indexed to a cubic phase with the fluorite structure conforming to theFm3mspace group [Yb2Zr1.21W0.41O6.65◻1.35called C-phase:a=5.1864(2) Å]. The second phase adopts the sheelite-type structure [Yb2ZrWO8called T-phase: space groupI41/a,a=5.1584(5), andc=10.8246(6) Å]. By taking into account the present compositions determined by EDS measurements, Rietveld structure refinements produce finalRBfactors of 0.015 and 0.044, andRwpfactors of 0.069 and 0.089, respectively. In order to characterize the microstructure of the materials (crystallite size and lattice distortion) at the nanometer scale, a study based on diffraction line broadening analysis applying the whole pattern refinement method was also undertaken with confidence. The results show smooth angular variations of the values of FWHMs, indicating that the microstructural properties are isotropic for the cubic and tetragonal oxides. More precisely, the results indicate that whatever the profile fitting approach used (“profile matching” procedure and Rietveld method), the reliability factorsRwpare systematically better with a combined size strain than with zero strain considerations. The strain magnitudes observed for the C-phase-850 °C as well as for the T-phase-900 °C should be viewed as realistic strain.

Powder diffraction investigations of some derivatives of benzophenone: Monomers for synthesis of new polyurethanes

Four aliphatic-aromatic diols with ether linkages [4, 4′-Bis(2-hydroxyethoxy)benzophenone, 4, 4′-Bis(3-hydroxypropoxy)benzophenone, 4, 4′-Bis(6-hydroxyhexyloxy)benzophenone, 4, 4′-Bis(11-hydroxyundecyloxy)benzophenone] and two aliphatic-aromatic diols with sulfur linkages [4, 4′-Bis[(2-hydroxyethyl)thio]benzophenone, 4, 4′-Bis[(3-hydroxypropyl)thio]benzophenone] have been characterized by X-ray powder diffraction. These diols can be used for synthesis of thermoplastic nonsegmented polyurethanes. Experimental 2θ peaks positions, relative peak intensities, values of d, and Miller indices as well as unit-cell parameters are presented.

A study on the structural and electrochemical properties of La 0.7− xNd xMg 0.3Ni 2.45Co 0.75Mn 0.1Al 0.2 ( x = 0.0–3.0) hydrogen storage alloys

The effects of substitution of Nd for La on the structural and electrochemical properties of the La 0.7− x Nd x Mg 0.3Ni 2.45Co 0.75Mn 0.1Al 0.2 ( x = 0.0–0.3) hydrogen storage alloys had been studied systematically. X-ray powder diffraction (XRD) investigation showed that all the alloys were mainly composed of the (La,Mg)Ni 3 phase and the LaNi 5 phase, and the lattice parameters and cell volumes of the component phases gradually decreased with increasing Nd content. The electrochemical studies revealed that the maximum discharge capacity decreased when x increases from 0.0 to 0.3. However, the cycling stability of the alloy electrodes was slightly improved. After 100 charge/discharge cycles, the capacity retention ( C 100/ C max) of the alloy electrode was increased from 78.2 to 81.3% with x increasing from 0.00 to 0.30. The high rate dischargeability of the alloy electrodes were first increased from 61.8% ( x = 0.00) to 70.1% ( x = 0.10) and then decreased to 53.7% ( x = 0.30) at the discharge current density I d = 1000 mA/g. Meanwhile, the results obtained from the electrochemical impedance spectroscopy, linear polarization, Tafel polarization, and hydrogen diffusion coefficient measurements indicated that the exchange current density I 0, the limiting current density I L and the hydrogen diffusion coefficient D of the alloy electrodes also first increased and then decreased with increasing Nd content, which implies that the electrochemical kinetics of the testing alloys could be effectively improved by partial substitution of Nd for La. Considering the overall effects of substitution of Nd for La on the La 0.7− x Nd x Mg 0.3Ni 2.45Co 0.75Mn 0.1Al 0.2 ( x = 0.00–0.30) alloy electrodes, the optimum composition was found to be x = 0.10.

A barium germanium 1,2-ethanediolato complex as precursor for barium metagermanate

The thermal behaviour of [Ba(HOC 2H 4OH) 2Ge(OC 2H 4O) 3] ( 2) as a BaGeO 3 precursor, and its phase evolution during thermal decomposition in different atmospheres are described herein. The precursor complex decomposes in air to a finely divided mixture of BaCO 3 and GeO 2, which subsequently reacts above 650 °C to orthorhombic BaGeO 3, transforming above 800 °C to hexagonal BaGeO 3. The shrinkage behaviour of BaGeO 3 compacts made from the as-prepared powders as well as from conventional mixed-oxide powders has been investigated. The samples were characterised by Fourier transformed infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), dilatometric measurements and thermoanalytic investigations (TG/DTA).

Investigations on the Polymorphism and Pseudopolymorphism of the Glucocorticoid Triamcinolone: New Findings for a Well-Known Drug

The glucocorticoid triamcinolone was investigated for polymorphism. If crystalline suspensions of the commercial available drug (form A) are stirred in different solvents, a new and hitherto unknown modification (form B) is always obtained. However, in water, a third form is isolated, which is a monohydrate (form C). Form B represents the thermodynamically most stable solvent-free modification at room temperature, whereas the commercially available form A is metastable. The stable form B crystallizes in the chiral, non-centrosymmetric monoclinic space group P21 with two crystallographically independent molecules in the asymmetric unit. In the crystal structure, the molecules are connected by O−H···O hydrogen bonding into a three-dimensional network. Dehydration of the modification C by thermogravimetry leads to its transformation into the metastable form A. The differential scanning calorimetry (DSC) thermograms of forms B and C exhibit three endothermic events, while form A shows two endothermic events. The last endothermic signal is assigned to the melting of the compounds. The X-ray powder diffraction investigations of the residues formed in these thermal events indicate the formation of at least one additional solvent-free modification.

Powder diffraction investigations of some organic hydrochlorides

Amantadine hydrochloride, p-aminophenol hydrochloride, and methylamine hydrochloride, compounds often studied in pharmacology, were investigated by means of powder diffractometry. The chemical formula of the first compound is C10H17N HCl and crystallizes in the monoclinic system, space group C2∕c (15) with lattice parameters a=2.0279(6) nm, b=1.1171(2) nm, c=9.759(4) nm, and β=109.00(3)°. p-Aminophenol hydrochloride C6H7NO HCl crystallizes in the orthorhombic system, space group P222 with lattice parameters a=0.6619(2) nm, b=0.88461(2) nm, and c=0.6101(2) nm. Methylamine hydrochloride CH5N∙HCl crystallizes in the tetragonal system, space group P4∕nmm (129) with lattice parameters a=b=0.6068(1) nm and c=0.50689(8) nm.

The funerary klinai of tomb 1 from Amphipolis and a sarcophagus from ancient Tragilos, eastern Macedonia: a physico-chemical investigation on the painting materials

Optical and SEM-EDS microscopy, X-ray powder diffraction and micro FT-IR spectroscopy investigations of the funerary klinai (couches) of Tomb 1 from Amphipolis and a stone sarcophagus from ancient Tragilos—two painted monuments made by Macedonian craftsmen of the Early Hellenistic period—identified the original materials and painting technique, as well as synthetic materials used as consolidants during past restoration treatments. The original organic binders and the superficial modern coatings have been identified by micro FT-IR spectroscopy applied directly to the sampled powders or tiny fragments and to their solvent—soluble fractions. The pigments identified on the couch of Amphipolis are: red and yellow ochre, cinnabar, Madder lake, paratacamite and antlerite, carbon black, calcium carbonate, kaolin and gypsum. The identification of egg and animal glue confirms the application of tempera and secco techniques. The detection of polymers such as polydimethylsiloxane, polyvinyl acetate and alkyd resins, is related to modern restoration products. The pigments attested on the paintings of the Tragilos' sarcophagus are: red and yellow ochre, Egyptian blue, malachite, carbon black, calcium carbonate and gypsum. The absence of organic binders combined with the constant presence of calcium carbonate in all the examined samples suggests the use of lime as the binding medium in the painted decoration of the sarcophagus. The presence of Paraloid B72 is related to recent conservation treatments.

Hydration of alkali-activated slag: comparison with ordinary Portland cement

A multi-method approach was used for the investigation and comparison of alkali-activated slag binders (AAS), pure slag and ordinary Portland cement (OPC). X-ray fluorescence, X-ray powder diffraction, granulometry, calorimetry, thermo-gravimetric analysis and environmental scanning electron microscope investigations of the microstructure with energy dispersive X-ray analyses were used to characterise the cements and their hydrate phases. In addition, the chemical composition of the pore solution, including the different sulphur-containing ions, was analysed. The precipitation mechanisms during binder hydration in the AAS and OPC systems exhibit significant differences: in AAS the formation of the ‘outer product’ C-S-H is much faster than in OPC. The high Si concentrations in the pore solution during the early hydration of AAS are related to the fast dissolution of Na-metasilicate. The fast reaction of Na is an important factor for the voluminous precipitation of C-S-H within the interstitial space already during the first 24 h. In addition to the Na-metasilicate component, the high fineness of the slag represents a further important factor for the fast hydration of AAS. The small slag particles (< 2 μm) are completely dissolved or hydrated within the first 24 h, whereas hydration of the larger particles is much slower. The fast formation of a gel-like matrix in AAS is the product of a fast ‘through solution’ precipitation, which contrasts with the slower dissolution-precipitation mechanism of a ‘topotactic’ growth of C-S-H in OPC. The chemical and mineralogical characterisation of solid and liquid phases and their changes with time are the basis for thermodynamic modelling of the corresponding hydration process, which is presented in a second paper.

Nanocrystalline Lanthanide Nitride Materials Synthesised by Thermal Treatment of Amido and Ammine Metallocenes: X‐ray Studies and DFT Calculations

The decomposition process of ammine lanthanide metallocenes was studied by X-ray diffractometry, spectroscopy and theoretical investigations. A series of ammine-tris(eta(5)-cyclopentadienyl)lanthanide(III) complexes 1-Ln (Lanthanide (Ln)=Sm, Gd, Dy, Ho, Er, Yb) was synthesised by the reaction of [Cp(3)Ln] complexes (Cp=cyclopentadienyl) with liquid ammonia at -78 degrees C and structurally characterised by X-ray diffraction methods, mass spectrometry and vibrational (IR, Raman) spectroscopy. Furthermore, amido-bis(eta(5)-cyclopentadienyl)lanthanide(III) complexes 2-Ln (Ln=Dy, Ho, Er, Yb) were synthesised by heating the respective ammine adduct 1-Ln in an inert gas atmosphere at temperatures of between 240 and 290 degrees C. X-ray diffraction studies, mass spectrometry and vibrational (IR, Raman) spectroscopy were carried out for several 2-Ln species and proved the formation of dimeric mu(2)-bridged compounds. Species 1-Ln are highly reactive coordination compounds and showed different behaviour regarding the decomposition to 2-Ln. The reaction of 1-Ln and 2-Ln with inorganic bases yielded lanthanide nitride LnN powders with an estimated crystallite size of between 40 and 90 nm at unprecedented low temperatures of 240 to 300 degrees C. Temperature-dependent X-ray powder diffraction and transmission electron microscopy (TEM) investigations were performed and showed that the decomposition reaction yielded nanocrystalline material. Structural optimisations were carried out for 1-Ln and 2-Ln by employing density functional (DFT) calculations. A good agreement was found between the observed and calculated structural parameters. Also, Gibbs free energies were calculated for 1-Ln, 2-Ln and the pyrolysis reaction to the nitride material, and were found to fit well with the expected ranges.

Facile Synthesis and Characterization of Functionalized, Monocrystalline Rutile TiO2Nanorods

Functionalized, monocrystalline rutile TiO2 nanorods were prepared from TiCl4 in aqueous solution under acidic conditions in the presence of dopamine, followed by aging and hydrothermal treatment at 150 degrees C. The surface-bound organic ligand controls the morphology as well as the crystallinity and the phase selection of TiO2. The presence of monocrystalline rutile TiO2 was confirmed by X-ray powder diffraction and HRTEM investigations. The as-prepared nanorods are soluble in water at pH <3. The surface functionalization was analyzed by IR and 1H NMR, confirming the presence of dopamine on the surface. The surface amine groups can be tailored further with functional molecules such as dyes. Confocal laser scanning microscopy (CLSM) was used to characterize the binding of the fluorescent dye 4-chloro-7-nitrobenzofurazan (NBD) to the functionalized surface of the TiO2 nanorods.

Single-crystal X-ray and neutron powder diffraction investigation of the phase transition in tetrachlorobenzene

The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. The diffraction experiments show a reversible phase change that occurs as a function of temperature with no apparent loss of sample quality on transition between the two phases. Neutron powder diffraction gives detailed information on the molecular structural changes and lattice parameters from 2 K to room temperature. The structure of the low-temperature form has been elucidated for the first time using single-crystal X-ray diffraction. Comparison of the alpha and beta structures show that they are both based on the same sheet motif, with the differences between the two being very subtle, except in terms of crystal symmetry. Detailed analysis of the structures revealed the changes required for inter-conversion. A computational polymorph search showed that these two sheet structures are more thermodynamically stable than alternative herringbone-type structures.

Electrochemical, Magnetic, and Structural Investigation of the Lix(MnyFe1-y)PO4 Olivine Phases

A series of synthetic heterosite−purpurite, (MnyFe1-y)PO4 (y < 0.8), with negligible disorder and impurities, was obtained by chemical oxidation of the well-crystallized isotypic tryphillite−lithiophilite series, Li(MnyFe1-y)PO4 (ordered olivine structure, space group Pnma). Comparative magnetic and X-ray/neutron powder diffraction investigations of the two solid−solution lines were performed as a function of Mn content to increase understanding of the electrochemical activity loss of Mn3+/Mn2+ in the Lix(MnyFe1-y)PO4 electrode system. Introducing Mn ions into the 4c site did not cause significant change in the local geometry of M2+O6 and PO4 polyhedra, while the M3+O6 octahedra became severely distorted with an increase in the number of Jahn−Teller active Mn3+ ions. The edge-sharing geometry of M3+O6 and PO4 polyhedra fixed the shared O3‘−O3‘ interatomic distance, causing selective strong elongation of the M3+−O3‘ distance with small shrinkage of other M3+−O1, M3+−O2, and M3+−O3 bond lengths. The overall...

Thermal analysis, powder diffraction and spectroscopic investigation of the solid phases of 1‐chloro‐2,2‐dimethylpropane

AbstractBy the substitution of one methyl group in Neopentane C(CH3)4 with a methylchlorid group the globular sphere is expanded in 1‐chloro‐2,2‐dimethylpropane (CH3)3C(CH2Cl). With the aid of DSC measurements, X‐ray powder diffraction, 1H NMR and 35Cl NQR measurements two orientationally disordered (plastic) phases were established. The low temperature structure was solved and a structural model of phase II is proposed. A mechanism to describe the reorientation in the different phases is given as well as a connectivity scheme between the phases is discussed. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

In situ neutron powder diffraction investigation of the hydration of tricalcium aluminate in the presence of gypsum

The hydration of a 1:3 molar ratio of tricalcium aluminate, Ca 3Al 2O 6, to gypsum, CaSO 4·2D 2O, was investigated at temperatures of 25, 50, and 80 °C using time-of-flight powder neutron diffraction combined with multiphase Rietveld structural refinement. It was shown that ettringite, Ca 6[Al(OD) 6] 2(SO 4) 3·∼26D 2O, was the first and only hydration product of the system, in contrast to a prior investigation which suggested the occurrence of a precursor phase prior to the formation of ettringite. Kinetics data showed that the hydration reaction is very sensitive to temperature: hydration at 25 °C was characterized by a single kinetic regime while hydration at higher temperatures consisted of two distinct kinetic regimes. The presence of two kinetic regimes was attributed to a change in either the dimensionality of the growth process or a change in the rate controlling mechanism in the hydration reaction.

Magnetic and transport properties ofBi0.5Ca0.5FexMn1−xO3 (0≤x≤0.6)

A series of Fe-substituted manganitesBi0.5Ca0.5FexMn1−xO3 (0≤x≤0.6) was synthesized by ceramic technology. The crystal lattice parameters change monotonicallywith increasing Fe substitution for Mn as found from x-ray powder diffraction and neutrondiffraction investigations at room temperature. Magnetic properties were studied between 5and 1300 K in fields up to 16 kOe. All the compounds are antiferromagnetic below acertain temperature, which decreases with increasing Fe substitution, and forx≥0.1 the antiferromagnetism is accompanied by a weak ferromagnetism. The charge/orbitalorder exists in the pure form for the compounds without or with very low Fe substitution(x = 0 and0.05). A new magnetic cluster state exists in the paramagnetic region of manganites with Fe substitutionx≥0.3, but only in the presence of magnetic field.The conductivity of compounds measured between 100 and 600 K is of semiconducting type,and there is no magnetoresistivity effect in fields up to 7 kOe.