Low-temperature X-ray Diffraction Research Articles

Doxycycline hydrate and doxycycline hydrochloride dihydrate – crystal structure and charge density analysis

Abstract High-resolution low-temperature X-ray diffraction experiments for doxycycline monohydrate and hydrochloride dihydrate have been performed. Translation-Libration-Screw (TLS) analysis for both crystal forms as well as the data from neutron diffraction experiment for hydrochloride combined with the Hansen-Coppens formalism resulted in precise charge density distribution models for both the zwitterionic monohydrate and a protonated hydrochloride crystal forms. Their detailed topological analysis suggested that the electron structure of doxycycline’s amide moiety undergoes significant changes during protonation due to formation of a very strong resonance-assisted hydrogen bond. A notably increased participation of amide nitrogen atom and hydrogen-accepting oxygen atom in the resonance upon doxycycline protonation was observed. A comparison of TLS- and neutron data-derived hydrogen parameters confirmed the experimental neutron data to be vital for proper description of intra- and inter-molecular interactions in this compound. Finally, calculated lattice and interaction energies quantified repulsive Dox-Dox interactions in the protonated crystal form of the antibiotic, relating with a good solubility of doxycycline hydrochloride relative to its hydrate.

Local corrugation and persistent charge density wave in ZrTe3 with Ni intercalation

The mechanism of emergent bulk superconductivity in transition metal intercalated ZrTe3 is investigated by studying the effect of Ni doping on the band structure and charge density wave (CDW). The study reports theoretical and experimental results in the range of Ni0.01ZrTe3 to Ni0.05ZrTe3. In the highest doped samples bulk superconductivity with Tc < TCDW is observed, while TCDW is strongly reduced. Relativistic ab-initio calculations reveal Ni incorporation occurs preferentially through intercalation in the van-der-Waals gap. Analysis of the structural and elec- tronic effects of intercalation, indicate buckling of the Te-sheets adjacent to the Ni site akin to a locally stabilised CDW-like lattice distortion. Experiments by low temperature x-ray diffraction, angle-resolved-photoemission spectroscopy (ARPES) as well as temperature dependent resistivity reveal the nearly unchanged persistence of the CDW into the regime of bulk superconductivity. The CDW gap is found to be unchanged in its extent in momentum space, with the gap size also unchanged or possibly slightly reduced on Ni intercalation. Both experimental observations suggest that superconductivity coexists with the CDW in NixZrTe3.

Modes of occurrence and origin of mineral matter in the Palaeogene coal (No. 19-2) from the Hunchun Coalfield, Jilin Province, China

Previous investigations on minerals and elements in coals from northeastern China are very scarce. This paper investigates the mineralogy and geochemistry of the Palaeogene No. 19-2 Coal, parting, and host rocks (roof and floor strata) in the Baliancheng mine, Hunchun Coalfield, Jilin Province, northeastern China. Samples collected from this coalfield were analyzed using low-temperature ashing plus X-ray diffraction analysis, scanning electron microscopy in combination with energy-dispersive X-ray spectrometry, X-ray fluorescence spectrometry, and inductively coupled plasma mass spectrometry. The investigated coal is of subbituminous A to high volatile bituminous rank (0.50–0.56% Ro,ran) and has a low sulfur content (0.25% on average). The mineral assemblage of the coal is dominated by kaolinite, illite and expandable clays, and quartz, with a trace of albite. In comparison with low-rank coals worldwide, the No. 19-2 Coal is enriched in Cs, V, and Mo.The minerals and elements in the coal and its roof and floor strata were mainly derived from the Mesozoic (Jurassic-Lower Cretaceous) intermediate-felsic volcanic rocks surrounding the coal basin. The parting within the coal seam is identified as a tonstein (bed of altered volcanic ash) based on its mineral composition, dominantly of vermicular and book-like kaolinite (plus smectite, high-temperature quartz, sanidine, apatite, and ilmenite), and its persistent distribution throughout the coal deposit. Based on these features and its chemical composition, this tonstein is deduced to have been derived from a Paleogene intermediate-felsic volcanic ash, which is characterized by some adakitic signatures of trace elements, and terrigenous materials. Normalized to the upper continental crust, the investigated samples (particularly the tonstein layer) show positive Eu anomalies inherited from the source rocks. This is in contrast to the coals, host rocks, and tonsteins with intermediate-felsic compositions in many other coal deposits, which are generally characterized by negative Eu anomalies. Geochemical and mineralogical features also indicate that the sedimentary materials of the tonstein, and, to a lesser extent, the floor horizon, were of aeolian origin, but those of most coal plies and roof strata were the result of aqueous deposition.

Low-Temperature Synthesis and Magnetostructural Transition in Antiferromagnetic, Refractory Nanoparticles: Chromium Nitride, CrN

Nanostructured chromium nitride (CrN), both a hard material and a high-melting compound that is used in the medical industry and for new energy-harvesting applications, was synthesized phase-pure for the first time via low-temperature solution synthesis in liquid ammonia. TEM analysis confirms the nanoscale character of CrN. The antiferromagnetic properties of the agglomerates of nanoparticles are discussed in comparison to literature data on the bulk materials. SQUID and DSC measurements show the transition from paramagnetic to antiferromagnetic at 258.5 K. In situ low-temperature X-ray diffraction patterns confirm the magnetostructural phase transition at this temperature, not seen before for nanoscale CrN. This structural distortion was calculated earlier to be driven by magnetic stress. The bottom-up synthesis of CrN allows for the production of nearly oxygen- and carbon-free and highly dispersed fine particles.

Thermal Expansion and Luminescent Properties of Triorthogermanates CaLa2-xEu x Ge3O10 (x = 0.0–0.6)

Solid solutions CaLa2-xEu x Ge3O10 (x = 0.0–0.6, Δx = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa2Ge3O10, they crystallize in the monoclinic system, space group P21/c, Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa2Ge3O10 crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established.

Synthesis and Characterization of Platinum-Cerium Oxide Nanocatalysts for Methanol Oxidation

CeO2-C(Vulcan) catalyst materials activated with Pt nanoclusters have been synthesized using different methods comprising microwave synthesis, reduction with hydrogen and reduction with NaBH4. The materials have been analyzed using low temperature nitrogen adsorption, X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy methods. Methanol oxidation has been studied using cyclic voltammetry, chronoamperometry and impedance methods. Very noticeable influence of catalyst surface structure and porosity, depending on the complex catalyst preparation conditions, has been demonstrated. High electrochemically active surface area values have been calculated. High current densities of MeOH oxidation have been established for several catalysts. Fitting of the impedance data has been performed, and the results have been discussed.

Термическое расширение и люминесцентные свойства триортогерманатов CaLa-=SUB=-2-x-=/SUB=-Eu-=SUB=-x-=/SUB=-Ge-=SUB=-3-=/SUB=-O-=SUB=-10-=/SUB=- (x=0.0-0.6)

AbstractSolid solutions CaLa_2- x Eu_ x Ge_3O_10 ( x = 0.0–0.6, Δ x = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa_2Ge_3O_10, they crystallize in the monoclinic system, space group P 2_1/ c , Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa_2Ge_3O_10 crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established.

In-field X-ray and neutron diffraction studies of re-entrant charge-ordering and field induced metastability in La0.175Pr0.45Ca0.375MnO3-δ

Low-temperature high-magnetic field (2 K, 8 T) (LTHM) powder X-ray diffraction (XRD) and time of flight powder neutron diffraction (NPD), low-temperature transmission electron microscopic (TEM), and resistivity and magnetization measurements have been carried out to investigate the re-entrant charge ordering (CO), field induced structural phase transitions, and metastability in phase-separated La0.175Pr0.45Ca0.375MnO3-δ (LPCMO). Low-temperature TEM and XRD studies reveal that on cooling under zero-field, paramagnetic Pnma phase transforms to P21/m CO antiferromagnetic (AFM) insulating phase below ∼233 K. Unlike reported literature, no structural signature of CO AFM P21/m to ferromagnetic (FM) Pnma phase-transition during cooling down to 2 K under zero-field was observed. However, the CO phase was found to undergo a re-entrant transition at ∼40 K. Neutron diffraction studies revealed a pseudo CE type spin arrangement of the observed CO phase. The low-temperature resistance, while cooled under zero-field, shows insulator to metal like transition below ∼105 K with minima at ∼25 K. On application of field, the CO P21/m phase was found to undergo field-induced transition to FM Pnma phase, which shows irreversibility on field removal below ∼40 K. Zero-field warming XRD and NPD studies reveal that field-induced FM Pnma phase is a metastable phase, which arise due to the arrest of kinetics of the first-order phase transition of FM Pnma to CO-AFM P21/m phase, below 40 K. Thus, a strong magneto-structural coupling is observed for this system. A field-temperature (H-T) phase-diagram has been constructed based on the LTHM-XRD, which matches very nicely with the reported H-T phase-diagram constructed based on magnetic measurements. Due to the occurrence of gradual growth of the re-entrant CO phase and the absence of a clear structural signature of phase-separation of CO-AFM P21/m and FM Pnma phases, the H-T minima in the phase-diagram of the present LPCMO sample has been attributed to the strengthening of AFM interaction during re-entrant CO transition and not to glass like “dynamic to frozen” transition.

In Ukrainian

Synthesis of mesoporous silicas of MCM-41 type with chemically immobilized β cyclodextrin-containing groups was realized by template sol-gel method in the presence of functional silane. The influence of reaction mixture composition used at β cyclodextrin-silane synthesis (molar ratio β cyclodextrin:3 aminopropyltriethoxysilane: 1,1'-carbonyldiimidazole) on chemical structure and arrangement of mesopores of resulting organosilica materials was proved. The enhancement of ethoxysilyl constituent in β cyclodextrin-silane used in sol-gel condensation leads to the formation of silicas with higher content of chemically immobilizedβ cyclodextrin-containing groups and less arranged mesopores. Structure of obtained materials was determined using chemical analysis, infrared spectroscopy, low-temperature nitrogen adsorption-desorption, X-ray diffraction, and transmission electron microscopy. With the aim to elucidate the contribution of β cyclodextrin-containing groups in the removal of azo dyes, sorption of methyl red and alizarin yellow on synthesized silicas was studied from phosphate buffer solutions in dependence of contact duration, equilibrium concentration, and pH of medium. The results were analyzed using Langmuir, Freundlich and Redlich-Peterson equations. It has been found that equilibrium sorption of methyl red and alizarin yellow on parent silica and silica with chemically immobilized β cyclodextrin containing groups is described by the Redlich-Peterson model.

Thermodynamic properties of myo-inositol

In the present work, the temperature dependence of heat capacity of vitamin B8 (myo-inositol) has been measured for the first time over the range from 8K to 340K by precision adiabatic vacuum calorimetry. Based on the experimental data, the thermodynamic functions of the vitamin B8, namely, the heat capacity, enthalpy H°(T)–H°(0), entropy S°(T)–S°(0) and Gibbs function G°(T)–H°(0) have been determined for the range from T→0K to 340K. The value of the fractal dimension D in the function of multifractal generalization of Debye’s theory of the heat capacity of solids was estimated and the character of heterodynamics of structure was detected. The enthalpy of combustion (−2747.0±2.1)kJ·mol−1 of the vitamin B8 was measured for the first time using high-precision combustion calorimeter. The standard molar enthalpy of formation in the crystalline state (−1329.3±2.3)kJ·mol−1 of B8 at 298.15K was derived from the combustion experiments. Using combination of the adiabatic and combustion calorimetry results the thermodynamic functions of formation of the myo-inositol at T=298.15K and p=0.1MPa have been calculated. The low-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion.

Structural and magnetic characterization of the Ni55Fe19Ga26 shape memory alloy thin film

The structural evolution of the Pulsed Laser Deposited Ni55Fe19Ga26 ferromagnetic Heusler alloy thin films has been studied as a function of substrate temperature. Room temperature Grazing Incidence X-Ray Diffraction (GIXRD) measurement reveals the polycrystalline nature of the films consisting of cubic austenite and non-cubic martensite phases. The cubic phase consists of the mixture of an ordered (L21) and disordered (γ) phases, the disordered phase gets suppressed with an increase in the substrate temperature while low temperature X-Ray Diffraction study shows structural modification of the samples. Field Emission Scanning Electron Microscopy (FESEM) study shows the droplet-like morphology of the films. Extended X-ray Absorption Fine Structure (EXAFS) study agrees with the X-ray diffraction results about the phase evaluation and further reveals the local structure information of the constituent atoms which leads to the hybridization effect and finally govern the macroscopic properties of the material. In addition, magnetization studies show the ferromagnetic nature of the film with a mixture of anti-ferromagnetic ordering arising due to antisite disorder of the atoms revealed by the EXAFS measurements.

Charge ordering in B-site Mo doped Pr0.20Sr0.80Mn1−xMoxO3−δ

The temperature dependent structural, transport and magnetic properties of Pr0.20Sr0.80Mn1−xMoxO3−δ (x = 0.0, 0.02, 0.04 and 0.10) have been studied using low-temperature x-ray and electron diffraction, resistivity and dc magnetization measurements. Unlike the undoped (x = 0) sample, which is cubic at room temperature, the Mo doped samples show phase coexistence of cubic (Pm3¯m) and tetragonal (I4/mcm;c/2>a) phases. The Mo doping stabilizes the tetragonal (I4/mcm) phase in the temperature range of 300–330 K. The tetragonality of the sample for x = 0.10 however appears to be of different kind, which further under goes an additional transition from tetragonal to orthorhombic (Fmmm) phase below 200 K. Transmission electron microscopy, employing electron-diffraction and high-resolution micro-structural imaging, clearly reveals the occurrence of charge-ordering (CO) for x = 0.04 and 0.10 samples with non-integral modulation along [110] type perovskite direction. The dc magnetization and resistivity data very well correlate with the observed structural and associated CO antiferromagnetic phase transitions. The increased stability of the distorted perovskite phases and the occurrence of CO are found to correlate with the increase in the Mn3+/Mn4+ ratio as a function of Mo6+ substitution. The possible role of effective B-site cation size in stabilizing the distorted perovskite phase has been discussed in terms of tolerance factor.

Stable Chloro- and Bromoxenate Cage Anions; [X3(XeO3)3]3- and [X4(XeO3)4]4- (X = Cl or Br).

The number of isolable compounds which contain different noble-gas-element bonds is limited for xenon and even more so for krypton. Examples of Xe-Cl bonds are rare, and prior to this work, no Xe-Br bonded compound had been isolated in macroscopic quantities. The syntheses, isolation, and characterization of the first compounds to contain Xe-Br bonds and their chlorine analogues are described in the present work. The reactions of XeO3 with [N(CH3)4]Br and [N(C2H5)4]Br have provided two bromoxenate salts, [N(C2H5)4]3[Br3(XeO3)3] and [N(CH3)4]4[Br4(XeO3)4], in which the cage anions have Xe-Br bond lengths that range from 3.0838(3) to 3.3181(8) Å. The isostructural chloroxenate anions (Xe-Cl bond lengths, 2.9316(2) to 3.101(4) Å) were synthesized by analogy with their bromine analogues. The bromo- and chloroxenate salts are stable in the atmosphere at room temperature and were characterized in the solid state by Raman spectroscopy and low-temperature single-crystal X-ray diffraction, and in the gas phase by quantum-chemical calculations. They are the only known examples of cage anions that contain a noble-gas element. The Xe-Br and Xe-Cl bonds are very weakly covalent and can be viewed as σ-hole interactions, similar to those encountered in halogen bonding. However, the halogen atoms in these cases are valence electron lone pair donors, and the σ*Xe-O orbitals are lone pair acceptors.

Superacids Based on Pentafluoroorthotellurate Derivatives of Aluminum.

The new Lewis acid Al(OTeF5 )3 and its acetonitrile adduct CH3 CN→Al(OTeF5 )3 were obtained by a simple one-step synthesis in batches of up to 15 g. Al(OTeF5 )3 and the adduct were characterized by vibrational spectroscopy (IR, Raman) and quantum-chemical calculations. Furthermore, five different salts of the new weakly coordinating anion [Al(OTeF5 )4 ]- were prepared in a two-step procedure. [Ph4 P][Al(OTeF5 )4 ], Cs[Al(OTeF5 )4 ], [Ph3 C][Al(OTeF5 )4 ], as well as the protonated benzene derivatives [C9 H13 ][Al(OTeF5 )4 ] and [C6 H7 ][Al(OTeF5 )4 ] were characterized by low-temperature single-crystal X-ray diffraction and NMR spectroscopy. Arenium salts have rarely been characterized in the solid state and were synthesized in this work in a simplified fashion.

Microstructural characterization of NiTi shape memory alloy produced by rotary hot forging

The thermomechanical processing of NiTi shape memory alloys usually involves several steps of hot and/or cold deformation. The present work presents the structural characterization of a Ni-rich NiTi alloy bar, produced by vacuum-induced melting and thermomechanical processing in laboratory scale, aiming at massive production in the future. This study focused on the first step of hot working at 800 °C during rotary forging. Microstructural characterization was performed using differential scanning calorimetry, high- and low-temperature X-ray diffraction (XRD) using a laboratory source and synchrotron XRD. Thus, it was possible to obtain the phase transformation characteristics of the material: the transformation temperatures and the transformation sequence. Proposed thermomechanical processing is intended for production of bars and wires that will be subsequently drawn to get thin wires, for different applications, including orthodontic arch wires.

Large porous particles for respiratory drug delivery. Glycine-based formulations

Large porous particles are becoming increasingly popular as carriers for pulmonary drug delivery with both local and systemic applications. These particles have high geometric diameters (5–30μm) but low bulk density (~0.1g/cm3 or less) such that the aerodynamic diameter remains low (1–5μm). In this study salbutamol and budesonide serve as model inhalable drugs with poor water solubility. A novel method is proposed for the production of dry powder inhaler formulations with enhanced aerosol performance (e.g. for salbutamol-glycine formulation the fine particle fraction (FPF≤4.7μm) value is 67.0±1.3%) from substances that are poorly soluble in water. To overcome the problems related to extremely poor aqueous solubility of the APIs, not individual solvents are used for spray freeze-drying of API solutions, but organic-water mixtures, which can form clathrate hydrates at low temperatures and release APIs or their complexes as fine powders, which form large porous particles after the clathrates are removed by sublimation. Zwitterionic glycine has been used as an additive to API directly in solutions prior to spray freeze-drying, in order to prevent aggregation of powders, to enhance their dispersibility and improve air-flow properties. The clathrate-forming spray freeze-drying process in the multi-component system was optimized using low-temperature powder X-ray diffraction and thermal analysis.

Studies on phase transition temperature of rare earth niobates Ln3NbO7 (Ln = Pr, Sm, Eu) with orthorhombic fluorite-related structure

The phase transition of ternary rare earth niobates Ln3NbO7 (Ln = Pr, Sm, Eu) was investigated by the measurements of high-temperature and low-temperature X-ray diffraction, differential scanning calorimetry (DSC) and differential thermal analysis (DTA). These compounds crystallize in an orthorhombic superstructure derived from the structure of cubic fluorite (space group Pnma for Ln = Pr; C2221 for Ln = Sm, Eu). Sm3NbO7 undergoes the phase transition when the temperature is increased through ca. 1080 K and above the transition temperature, its structure is well described with space group Pnma. For Eu3NbO7, the phase transition was not observed up to 1273 K Pr3NbO7 indicates the phase transition when the temperature is increased through ca. 370 K. The change of the phase transition temperature against the Ln ionic radius for Ln3NbO7 is quite different from those for Ln3MO7 (M = Mo, Ru, Re, Os, or Ir), i.e., no systematic relationship between the phase transition temperature and the Ln ionic radius has been observed for Ln3NbO7 compounds.

Phase Transformation, Vibrational and Electronic Properties of K2Ce(PO4)2: A Combined Experimental and Theoretical Study.

Herein we report the high-temperature crystal chemistry of K2Ce(PO4)2 as observed from a joint in situ variable-temperature X-ray diffraction (XRD) and Raman spectroscopy as well as ab initio density functional theory (DFT) calculations. These studies revealed that the ambient-temperature monoclinic (P21/n) phase reversibly transforms to a tetragonal (I41/amd) structure at higher temperature. Also, from the experimental and theoretical calculations, a possible existence of an orthorhombic (Imma) structure with almost zero orthorhombicity is predicted which is closely related to tetragonal K2Ce(PO4)2. The high-temperature tetragonal phase reverts back to ambient monoclinic phase at much lower temperature in the cooling cycle compared to that observed at the heating cycle. XRD studies revealed the transition is accompanied by volume expansion of about 14.4%. The lower packing density of the high-temperature phase is reflected in its significantly lower thermal expansion coefficient (αV = 3.83 × 10-6 K-1) compared to that in ambient monoclinic phase (αV = 41.30 × 10-6 K-1). The coexistences of low- and high-temperature phases, large volume discontinuity in transition, and large hysteresis of transition temperature in heating and cooling cycles, as well as drastically different structural arrangement are in accordance with the first-order reconstructive nature of the transition. Temperature-dependent Raman spectra indicate significant changes around 783 K attributable to the phase transition. In situ low-temperature XRD, neutron diffraction, and Raman spectroscopic studies revealed no structural transition below ambient temperature. Raman mode frequencies, temperature coefficients, and reduced temperature coefficients for both monoclinic and tetragonal phases of K2Ce(PO4)2 have been obtained. Several lattice and external modes of rigid PO4 units are found to be strongly anharmonic. The observed phase transition and structures as well as vibrational properties of both ambient- and high-temperature phases were complimented by DFT calculations. The optical absorption studies on monoclinic phase indicated a band gap of about 2.46 eV. The electronic structure calculations on ambient-temperature monoclinic and high-temperature phases were also carried out.

Characterization and behavior of water in lignocellulosic and microalgal biomass for thermochemical conversion

Behavior and nature of water in biomass significantly influence the thermochemical conversion processes. This study investigates the characteristics and behavior of water in lignocellulosic and microalgal biomass using differential scanning calorimetry (DSC) and low-temperature X-ray diffraction (XRD) methods. Pine sawdust (PS), peanut shell (PT), and microalgae (MA) samples with different water contents were used and analyzed systematically. Freezable free water was detected in all biomass samples through DSC analysis. Different from PS and PT, a shift in the position of freezable free water peaks was observed during freezing process of MA on DSC, which was attributed to the strong hydrophilicity of this biomass. No freezable bound water was observed in the biomass samples. However, significant amount of non-freezable bound water was detected in all biomass samples. The freezing enthalpies of freezable free water in PS, PT, and MA ranged between 319.04 and 297.7kJ/kg which were in good agreement with that of bulk water. The boundary between freezable and non-freezable water in the biomass samples was clearly defined combining DSC and XRD analyses. The amount of non-freezable bound water in biomass samples directly correlated with the relative concentration of oxygen functional groups in biomass samples.

Charge Ordering Transitions of the New Organic Conductors δm- and δo-(BEDT-TTF)2TaF6

Structural, transport, and magnetic properties of new organic conductors composed of (BEDT-TTF) 2 TaF 6 , where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene, have been investigated. Two δ -type polymorphs, monoclinic and orthorhombic phases are obtained by the electrocrystallization. Both phases show a semiconductor-insulator phase transition at 276 K and 300 K for the monoclinic and orthorhombic phases, respectively; the ground state of both salts is a nonmagnetic insulating state. The low-temperature X-ray diffraction measurements show two-fold superlattice reflections in the intercolumnar direction. The low-temperature crystal structures show a clear charge ordered state, which is demonstrated by the molecular shape and intramolecular bond lengths. The observed checkerboard charge ordered state is in agreement with the charge ordering in a dimer Mott insulator. If we distinguish between the monoclinic and orthorhombic phases, the transition temperature of the δ -type (BEDT-TTF) 2 M F 6 conductors ( M = P, As, Sb, and Ta) increases continuously with increasing the anion volume.