Low-temperature Powder X-ray Diffraction Research Articles

Raman studies of hydrogen trapped in As4O6·2H2 at high pressure and low temperature.

Raman spectroscopic measurements of the arsenolite-hydrogen inclusion compound As4O6·2H2 were performed in diamond anvil cells at high pressure and variable temperature down to 80 K. The experimental results were complemented by ab initio molecular dynamics simulations and phonon calculations. Observation of three hydrogen vibrons in As4O6·2H2 is reported in the entire temperature and pressure range studied (up to 24 GPa). While the experiments performed with protium and deuterium at variable temperatures allowed for the assignment of two vibrons as Q1(1) and Q1(0) transitions of ortho and para spin isomers of hydrogen trapped in the inclusion compound, the origin of the third vibron could not be unequivocally established. Low-temperature spectra revealed that the lowest-frequency vibron is actually composed of two overlapping bands of Ag and T2g symmetries dominated by H2 stretching modes as predicted by our previous density functional theory calculations. We observed low-frequency modes of As4O6·2H2 vibrations dominated by H2 "librations," which were missed in a previous study. A low-temperature fine structure was observed for the J = 0 → 2 and J = 1 → 3 manifolds of hydrogen trapped in As4O6·2H2, indicating the lifting of degeneracy due to an anisotropic environment. A non-spherical distribution was captured by molecular dynamics simulations, which revealed that the trajectory of H2 molecules is skewed along the crystallographic ⟨111⟩ direction. Last but not least, low-temperature synchrotron powder x-ray diffraction measurements on As4O6·2H2 revealed that the bulk structure of the compound is preserved down to 5 K at 1.6 GPa.

Freeze-drying process for the design of porous formulations based on bismuth-potassium-ammonium citrate

The objective of this study was to find optimal freeze-drying process parameters to design porous and friable freeze-dried bismuth-potassium-ammonium citrate (FD BPAC) with improved dissolution behavior. The nucleation and melting temperatures of frozen BPAC solution in water and tert-butanol/water co-solvent system were studied with use of thermal analysis. The phases that resulted on cooling were studied by low-temperature powder x-ray diffraction. BPAC formed an amorphous freeze concentrate on cooling and remained amorphous during freeze-drying and subsequent storage. The nucleation of colloidal bismuth subcitrate (CBS) in the FD BPAC and starting BPAC systems in 0.1 M and 0.01 M HCl was studied by dynamic light scattering (DLS) method. The proposed preparation method of FD BPAC can be the basis for design of formulations with enhanced dissolution rate for bismuth-based triple/quadruple therapy, where FD BPAC simultaneously act as a carrier and an active ingredient.

Investigation of new magnetoelastic and magnetic transitions accompanied with magnetoelectric coupling in multiferroic

A new multiferroic solid solution has been developed and characterized for structure, phase transition, magnetoelectric and magnetoelastic coupling. Temperature dependent measurement of dc-magnetization on ceramic shows two magnetic transitions one around 42 K and the second at 130 K. The real part of dielectric permittivity exhibits step like change at the magnetic anomaly temperature (130 K) which indicates the presence of magnetoelectric coupling. The change in the value of dielectric permittivity on the application of magnetic field confirms the presence of magnetoelectric coupling in ceramic. The room temperature polarization (P)-electric field (E) hysteresis loop measurement shows week ferroelectric nature of sample while the magnetization (M) versus magnetic field (H) measurement suggest weakly ferromagnetic character. The ferroelectric nature of sample was further confirmed by calculating remanent polarization using PUND measurement. The Rietveld structural analysis of low temperature x-ray powder diffraction data does not reveal any crystallographic phase transition in terms of peak splitting or new reflections. However, temperature dependence of lattice parameters, tetragonality, unit cell volume, octahedral tilt angle (), bond length and bond angles reveal discontinuous changes at both the magnetic transitions observed in temperature dependence of magnetization. This confirms that both the magnetic anomalies (around 42 K and 130 K) exhibit magnetoelastic coupling accompanied with isostructural transitions.

Structural instability in CePd2(Al,Ga)2 and LaPd2(Al,Ga)2

The present study is focused on the structural phase transition in (La,Ce)Pd2Al2−xGax investigated by low temperature X-ray powder diffraction. All parent compounds crystallize in the tetragonal CaBe2Ge2 structure type (P4/nmm, 129) at room temperature and undergo structural phase transitions at low temperatures. Rietveld analysis of the measured patterns shows that the low temperature structures of (La,Ce)Pd2Al2 and (La,Ce)Pd2Ga2 have the same space groups and Wyckoff positions, but exhibit different magnitude of distortion and different characteristics of the structural transition. A small continuously appearing distortion is present in the Al parent compounds while the Ga ones exhibit a large discontinuously appearing distortion. These low temperature structures can be described using the Cmme, 67 space group which is translationengleiche subgroup of the tetragonal P4/nmm, 129 space group. The concentration dependence of the temperature where the distortion occurs has a minimum or is almost suppressed at a concentration of x∼0.4 (cerium series) and x∼1.6 (lanthanum series). To support our experimental findings we also present density function theory calculations which confirm the structural stability as experimentally observed. We discuss the impact of structural properties in the studied series on the previously observed development of physical properties such as superconductivity and magnetic excitations in neutron scattering spectra.

Thermal Behavior of Antiferromagnets FeBO3 and Fe3BO6 at Negative Temperatures

The thermal behavior of antiferromagnets FeBO3 and Fe3BO6 is investigated according to the low-temperature powder X-ray diffraction data. Unit cell parameters were refined by the Rietveld method. The coefficients of thermal expansion are calculated. The interrelation between the expansion and crystal structure is described.

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.

Low-temperature high magnetic field powder x-ray diffraction setup for field-induced structural phase transition studies from 2 to 300 K and at 0 to 8-T field.

A low-temperature and high magnetic field powder x-ray diffractometer (XRD) has been developed at UGC-DAE CSR (UGC: University Grant Commission, DAE: Department of Atomic Energy, and CSR: Consortium for scientific research), Indore, India. The setup has been developed around an 18 kW rotating anode x-ray source delivering Cu-Kα x-rays coming from a vertical line source. It works in a symmetric θ-2θ parallel beam geometry. It consists of a liquid helium cryostat with an 8 T split-pair Nb-Ti superconducting magnet comprising two x-ray windows each covering an angular range of 65°. This is mounted on a non-magnetic type heavy duty goniometer equipped with all necessary motions along with data collection accessories. The incident x-ray beam has been made parallel using a parabolic multilayer mirror. The scattered x-ray is detected using a NaI detector through a 0.1° acceptance solar collimator. To control the motions of the goniometer, a computer programme has been developed. The wide-angle scattering data can be collected in a range of 2°-115° of 2θ with a resolution of ∼0.1°. The whole setup is tightly shielded for the scattered x-rays using a lead hutch. The functioning of the goniometer and the artifacts arising possibly due to the effect of stray magnetic field on the goniometer motions, on the x-ray source, and on the detector have been characterized by collecting powder XRD data of a National Institute of Standards and Technology certified standard reference material LaB6 (SRM-660b) and Si powder in zero-field and in-field conditions. Occurrence of field induced structural-phase transitions has been demonstrated on various samples like Pr0.5Sr0.5MnO3, Nd0.49Sr0.51MnO3-δ and La0.175Pr0.45Ca0.375MnO3 by collecting data in zero field cool and field cool conditions.

Low-temperature powder X-ray diffraction measurements in vacuum: analysis of the thermal displacement of copper

A serious limitation of the all-in-vacuum diffractometer reported by Straasø, Dippel, Becker & Als-Nielsen [J. Synchrotron Rad.(2014),21, 119–126] has so far been the inability to cool samples to near-cryogenic temperatures during measurement. The problem is solved by placing the sample in a jet of helium gas cooled by liquid nitrogen. The resulting temperature change is quantified by determining the change in unit-cell parameter and atomic displacement parameter of copper. The cooling proved successful, with a resulting temperature of ∼95 (3) K. The measured powder X-ray diffraction data are of superb quality and high resolution [up to sinθ/λ = 2.2 Å−1], permitting an extensive modelling of the thermal displacement. The anharmonic displacement of copper was modelled by a Gram–Charlier expansion of the temperature factor. As expected, the corresponding probability distribution function shows an increased probability away from neighbouring atoms and a decreased probability towards them.

High-Pressure Synthesis of Cd(NH₃)₂[B₃O₅(NH₃)]₂: Pioneering the Way to the Substance Class of Ammine Borates.

To date, the access to the substance class of borates containing nitrogen, for example, nitridoborates, oxonitridoborates, or amine borates, was an extreme effort owing to the difficult starting materials and reaction conditions. Although a number of compounds containing boron and nitrogen are known, no adduct of ammonia to an inorganic borate has been observed so far. A new synthetic approach starting from the simple educts CdO, B2O3, and aqueous ammonia under conditions of 4.7 GPa and 800 °C led to the synthesis of Cd(NH3)2[B3O5(NH3)]2 as the first ammine borate. We thoroughly characterized this compound on the basis of low-temperature single-crystal and powder X-ray diffraction data, IR and Raman spectroscopy, and by quantum theoretical calculations. This contribution shows that the adduct of NH3 to the BO3 group of a complex B-O network can be stabilized, opening up a fundamentally new synthetic route to nitrogen-containing borates.

Microstructure, Phase Transformations, and Properties of Hot-Extruded Ni-Rich NiTi Shape Memory Alloy

Processing of NiTi shape memory alloys strongly influences their microstructure, phase transformations, mechanical, and shape memory properties. Hot forging, hot swaging, or hot rolling are efficient techniques for obtaining the desired shape, but during multiple operations the material must be heated and worked in the temperature range from 700 to 900 °C. During these processes, intense oxidation takes place. In order to reduce it, the hot-pack working is applied. The hot extrusion is more effective for reduction of ingot, billet, and rod diameters than hot forging, hot swaging, or hot rolling. Also, during hot extrusion the material surface undergoes considerably less oxidation. In the present work, results of the characterization by differential scanning calorimetry, low-temperature x-ray powder diffraction, and three-point bending and free recovery ASTM F2082-06 tests of the samples after hot direct extrusion and heat treatment are presented. The obtained alloy after hot direct extrusion exhibits desired shape memory effect. The phase transformations during cooling and heating cycle occur with the presence of the R phase. The range of the characteristic temperatures for the obtained material gives possibility for further medical applications. After annealing at 400 and 500 °C, the characteristic temperatures shift to higher values.

Structural and thermodynamic properties of Fe1.12Te with multiple phase transitions

The parent compound of iron chalcogenide superconductors, Fe1+yTe, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe1.12Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11≤y≤0.13. On cooling, an antiferromagnetic transition, TN≈57 K is observed. A closer examination of powder diffraction data suggests that the transition at TN is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at TS with TS<TN, where an onset of monoclinic distortion is observed. The results point to a strong magneto-structural coupling in this material.

Low-Temperature XRD Study of Phase Transformations in NiTi and TiNiCo Shape Memory Alloys Used for the Preparation of the Prototypes of Medical Implants

The NiTi shape memory alloys with ternary additions of Co are being considered for future applications in the construction of medical products. In this study the commercially available Ni50.8Ti49.2 medical alloy and Ti50Ni48.7Co1.3 alloy obtained by the conventional VIM technique, were used to prepare shape memory and superelastic staples. The phase transformations in the wires of those alloys after various thermo-mechanical and thermal treatments have been defined by the differential scanning calorimetry (DSC) method and three-point bending and free recovery ASTM F2082-06 tests. In this work the courses of phase transformations in the studied alloys were investigated by means of the low-temperature X-ray powder diffraction method. In both alloys after cold working and annealing during cooling two phase transformations occur: from parent B2-phase to rhombohedral R-phase and monoclinic B19’ martensite phase. Such phase transformations are fully reversible during heating and the obtained characteristic temperatures from DSC and X-ray powder diffraction measurements are in good agreement.

Kinetics of Methane Hydrate Decomposition Studied via in Situ Low Temperature X-ray Powder Diffraction

Gas hydrate is known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Based on results from the decomposition of three nominally similar methane hydrate samples, the kinetics of two regions, 180-200 and 230-260 K, within the overall decomposition range 140-260 K, were studied by in situ low temperature X-ray powder diffraction. The kinetic rate constants, k(a), and the reaction mechanisms, n, for ice formation from methane hydrate were determined by the Avrami model within each region, and activation energies, E(a), were determined by the Arrhenius plot. E(a) determined from the data for 180-200 K was 42 kJ/mol and for 230-260 K was 22 kJ/mol. The higher E(a) in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions.

A cautionary tale on the use of GE-7031 varnish: low-temperature thermal expansion studies of ScF3

GE-7031 varnish, a commonly used low-temperature adhesive and electrical insulator owing to its high thermal conductivity and mechanical strength at low temperatures, was used as a sample matrix for low-temperature powder X-ray diffraction measurements of the negative thermal expansion (NTE) material ScF3. When ScF3powder was mixed with GE-7031 varnish, an unexpected cubic to rhombohedral phase transition in the ScF3sample was observed at ∼50 K, and it exhibited smaller low-temperature unit-cell volumes than samples without the varnish matrix. Experimental observations and quantitative estimates suggest that these anomalies are the result of stress induced by a thermal expansion mismatch between the varnish matrix (large positive coefficient of thermal expansion, CTE) and ScF3(quite large negative CTE). The use of GE-7031 varnish as a sample matrix for low-temperature measurements should be approached with caution if a large thermal expansion mismatch is expected.

The change of anisotropy in TbNi(Al,In) compounds studied by low temperature x-ray diffraction

We have investigated the transition between the easy-axis and easy-plane type of magnetocrystalline anisotropy in the TbNi(Al,In) series. These compounds crystallize in the hexagonal ZrNiAl-type structure and order magnetically at low temperatures. TbNiAl is an antiferromagnet below 47 K with the moments aligned along the c-axis, whereas TbNiIn orders magnetically below 70 K with moments perpendicular to the c-axis. The presented study is based mainly on the low temperature x-ray powder diffraction performed in presence of external magnetic field. We have revealed that the transition between both types of anisotropy occurs in compounds with In concentration around 30%.

Properties of new low melting point quaternary ammonium salts with bis(trifluoromethanesulfonyl)imide anion

Eight new monocationic quaternary ammonium (QA) salts with the bis(trifluoromethanesulfonyl)imide (TFSI) anion were prepared by metathesis using our previously reported QA halides as precursors. New salts were characterized both in liquid and solid state using 1H and 13C NMR techniques, mass spectroscopy and elemental analysis together with X-ray diffraction and thermoanalytical methods. In addition, residual water content, viscosity and conductivity measurements were made for three of the room-temperature ionic liquids (RTILs). The crystal structures of three compounds were determined by X-ray single crystal diffraction. Powder diffraction was used to study the crystallinity of the solid salts and to compare structural similarities between the single crystals and the microcrystalline bulk powders. Three of the salts are liquid below room temperature, having broad liquid ranges (∼300 °C), and in total five out of eight salts melt below 100 °C. Moreover, powder diffraction data of the two RTILs were able to be measured at sub-ambient temperatures using in situ low-temperature powder X-ray diffraction revealing high crystallinity on both RTILs below their freezing point. The RTILs presented relatively high conductivities (∼0.1–0.2 S m −1) and moderate to relatively low viscosities. The determined physicochemical properties of the reported ILs suggest their applicability on various applications such as heat transfer fluids, high temperature synthesis and lubricants.

Experimental and theoretical study of the magnetic and structural properties ofEr0.75Tb0.25Al2

The ${\text{Er}}_{0.75}{\text{Tb}}_{0.25}{\text{Al}}_{2}$ alloy has been investigated by x-ray powder diffraction, magnetization, and ac magnetic-susceptibility measurements. The low-field magnetization measured as a function of temperature indicates a ferromagnetic transition at $\ensuremath{\sim}36\text{ }\text{K}$ and another transition with thermal hysteresis at $\ensuremath{\sim}18\text{ }\text{K}$. The ac magnetic-susceptibility measurements show frequency dependence below the ferromagnetic transition temperature, ${T}_{\text{C}}$. Low-temperature x-ray powder-diffraction measurements suggest that although no structural transformation occurs around 18 K, a steplike anomaly in the lattice parameters does exist in the vicinity of the transition. First-principles electronic-structure calculations show anomalous density of states at the Fermi level. The results are comparable with the previously reported ${\text{Er}}_{0.75}{\text{Dy}}_{0.25}{\text{Al}}_{2}$ alloy, thus supporting an earlier assumption that mixing two rare-earth ions with opposite signs of second-order Steven's factor in $R{\text{Al}}_{2}$ alloys creates a competition between the magnetoelastic and quadrupolar interactions, giving rise to multiple magnetic ordering phenomena.

A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

Abstract The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis. The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe–Mg-rich fluids during early diagenesis. The high pyrite (Sp,d = 8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids. Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5 μg/g), V (121 μg/g), Cr (33.6 μg/g), Co (27.2 μg/g), Ni (83.5 μg/g), Cu (48.5 μg/g), Ga (17.3 μg/g), Y (68.3 μg/g), Zr (444 μg/g), Nb (23.8 μg/g), and REE (392 μg/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that enriched trace elements above were largely derived from mafic tuffs, in addition to a minor amount from the Kandian Oldland.

Crystal Growth and Structure and Magnetic Properties of the 5d Oxide Ca3LiOsO6: Extended Superexchange Magnetic Interaction in Oxide

Crystals of the newly synthesized compound Ca(3)LiOsO(6) were grown by a flux method using LiCl and KCl, followed by single-crystal X-ray diffraction (XRD), low-temperature powder XRD, and measurements of ac and dc magnetic susceptibility and specific heat. The data indicate that Ca(3)LiOsO(6) has a fully opened electronic gap with an antiferromagnetic ordered state, consistent with suggestions from the first-principles study. The observed magnetic transition temperature is 117 K, too high to be caused only by a direct spin-spin interaction. It appears that the original superexchange magnetic path Os-O-Os is absent; thus, the extended superexchange path (Os-O)-(O-Os) can be expected to be responsible for the 117 K magnetic order. If this is true, Ca(3)LiOsO(6) would be highly valuable to study the nature of extended superexchange magnetic interactions in solids.

Possible charge-density wave transition inPrPt2Si2

The physical properties of the ternary intermetallic compound ${\text{PrPt}}_{2}{\text{Si}}_{2}$ have been investigated by specific-heat and electrical-resistivity measurements under pressure up to 2.85 GPa. Two phase transitions at ${T}_{0}=88\text{ }\text{K}$ and ${T}_{x}=54\text{ }\text{K}$ are inferred from anomalies in the electrical resistivity. Only the transition at ${T}_{0}$ is visible in the specific-heat data. A strong thermal hysteresis suggests a first-order character of both transitions. The resistivity anomaly at ${T}_{0}$ has the resemblance to a charge-density wave transition. Furthermore, low-temperature powder x-ray diffraction data do not show any signature of a structural phase transition. The nonmagnetic character of both transitions is confirmed by the absence of a signature in magnetic susceptibility and a magnetic field independent transition temperature. Application of pressure suppresses ${T}_{0}(p)$ but has a very weak effect on ${T}_{x}(p)$.