X-ray diffraction study of the palladium-carbon system

The Pd-C solid solution was studied by wide angle X-ray diffraction. The Debye-Waller parameter and lattice strains were estimated for both carbon free and carburized palladium. Nearly equal values of the mean displacement of about 0.093 Å was found for palladium atoms in these two cases, a value of 0.17 Å was estimated for the carbon atoms in the carburized sample. An increase of lattice strains was found after decarbonization. The location of carbon atoms in the octahedral voids was confirmed.     

X-ray diffraction study of thermal vacancies in solid helium-3

Thermal vacancy concentrations in solid ³He have been directly measured by x-rays over a wide range of molar volumes in the bcc phase and one molar volume in the hcp phase. Values of the vacancy free energies and free volumes of formation have been obtained, and comparison with NMR and ultrasonic studies yields information about vacancy motion in the two phases of the solid.     

X-ray diffraction studies on dilute solid solution of NaCl with Ag impurities

Abstract

X-ray investigations of Bragg scattering measurements have been carried out on the dilute solid solutions of Ag _x Na_1?x Cl for x = 0.03 and 0.10. The integrated intensities are measured on spherical single crystals, using a home-built manual X-ray diffractometer. The analysis of experimental data indicates an enhancement of Debye-Waller factor in this system. The size effect distortion factors evaluated are compared with the calculated values on the basis of different theoretical models and the results are discussed. The measured cell constant and density data indicate the existence of vacancies in these crystals.     

An X-ray diffraction study of liquid chlorine

The static structure of liquid chlorine at room temperature is investigated by means of X-ray diffraction. From comparisons with previous neutron and X-ray data, it appears that most of the discrepancies present in the liquid structure factor between neutron and X-ray studies have been removed. Some experimental difference in the two structure factors still remains and one possible explanation is that the electron density distribution of liquid chlorine differs from that derived within the independent atom approximation.     

Anomalous temperature dependence of conductivity and X-ray diffraction in CuxPb1−xBr2−x solid solution

The temperature dependence of the electrical impedance of Cu_xPb_1−xBr_2−x was measured. Both conductivity and relaxation time of ion migration at two temperature regions above and below 145 °C showed anomalous differences. Intensity measurements of X-ray diffraction were also carried out varying the temperature over the range from 30 to 200 °C. The integrated intensity for Bragg reflection abruptly decreased above 145 °C with increasing temperature. We obtained a mean square displacement of atoms, resulting from a Debye-Waller factor. It is therefore concluded that the anomalous temperature dependence of the conductivity above 145 °C is due to anharmonic vibration of the Cu atom. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Influence of interdiffusion of heteromaterials on X-ray diffraction by superlattice with stacking fault

X-ray dynamic diffraction on a superlattice with a stacking fault between the layers is considered theoretically in the case of interdiffusion of superlattice components. Expressions for the X-ray reflectance within satellite limits, depending on the wave’s phase jump on the stacking fault, its depth and the extent of interdiffusion of superlattice components are obtained.     

Temperature and magnetic field induced structural transformation in Si-doped CeFe2: An in-field X-ray diffraction study

Using the X-ray powder diffraction technique at various temperatures and applied magnetic fields, we have studied the magnetostructural properties of Ce(Fe_0.95Si_0.05)₂. The X-ray diffraction data establish quantitative relationships between bulk magnetization and the evolution of structurally distinct phases with magnetic field and temperature, and confirm the distinct features of a first-order phase transition such as supercooling and superheating, metastability, and phase co-existence of different structural polymorphs. We observe the lattice volume mismatch across the structural phase transition, which appears to be the cause for the step behavior of the magnetization isotherms at low temperatures. The present study shows that the lattice distortion has to be treated explicitly, like spin, along with the effects of lattice–spin coupling to account for the magnetization behavior of this system. This structure template can resolve the issue of kinetics in this material as observed in different time scale measurements and with different experimental protocols.     

Thermal equation-of-state of osmium: a synchrotron X-ray diffraction study

The pressure-volume-temperature behavior of osmium was studied at pressures and temperatures up to 15 GPa and 1273 K. In situ measurements were conducted using energy-dispersive synchrotron X-ray diffraction in a T-cup 6-8 high pressure apparatus. A fit of room-temperature data by the third-order Birch-Murnaghan equation-of-state yielded isothermal bulk modulus K₀=435(19) GPa and its pressure derivative K′₀=3.5(0.8) GPa. High-temperature data were analyzed using Birch-Murnaghan equation of state and thermal pressure approach. The temperature derivative of bulk modulus was found to be −0.061(9) GPa K⁻¹. Significant anisotropy of osmium compressibility was observed.     

X-ray diffraction evidence of the single solid solution character of bi-metallic Pt-Pd catalyst particles on an amorphous SiO2 substrate

An X-ray diffraction study was carried out on powders of a series of catalysts prepared from aqueous solutions of H₂PtCl₆ and PdCl₄ and amorphous SiO₂ with different concentrations in weight of Pt and Pd at about 4% in overall metallic weight. Measurements of the position of high angle Bragg reflections in the diffractograms show evidence of the fact that the small catalyst particles are bi-metallic Pt-Pd crystals having a face-centred cubic Bravais lattice. The lattice constant of these crystals was found to change with the relative concentration of Pt and Pd by following the Vegard’s rule. This correlation leads to the conclusion that the bi-metallic catalyst particles are made of a single solid solution of Pt and Pd atoms in the whole range of relative concentrations. Relative concentrations of these metals in the samples under study were determined by using energy dispersive X-ray spectrometry and their values were found to be close to the stochiometric relative concentrations in weight of the metals in the precursor aqueous solution. An average size of about 96 Å was estimated for the bi-metallic particles from the full-width at half-maximum value measured for the (2 0 0) diffractometric curve.     

High-pressure X-ray diffraction study of 2-methyl 1,3-cyclopentanedione crystals

Abstract

2-Methyl-1, 3-cyclopentanedione (C₆H₈O₂-enol form) crystals have been studied at high pressures to 3.01(5) GPa by single crystal X-ray diffraction. The pressure dependence of the unit-cell dimensions is strongly anisotropic and non-linear, the largest relative changes are observed for & perpendicular to the planes comprising the planar chains of the hydrogen-bonded molecules. The crystal structure has been determined at 1.50, 2.40 and 3.01 GPa. The structure is very stable, the main structural change with pressure is the compression of intermolecular distances including the O … O hydrogen bond—but the position of the molecule in the unit cell remains unchanged. Some systematic changes of the bond lengths (in the limit of statistical significance) can be noted. The structure has been compared with the structures of 1,3-cyclopentanedione and 1,3-cyclohexanedione (enol forms), both undergoing pressure induced phase transitions. The exceptional stability of the 2-methyl- 1,3-cyclopentanedione crystal can be explained on the basis of its structure: energetically favourable orientation of the dipole moments of the molecules of close neighbouring chains. The R-factor/number of unique reflections for the structure determinations at 1.50, 2.40 and 3.01 GPa are 0.103/153,0.093/142 and 0.097/139, respectively. Over 3.01 GPa the unit cell is compressed to less than 84% of its ambient-pressure volume. The root-mean-square displacements of the atoms decreased on average by the factor of 0.75 at 1.50 GPa and 0.74 at 2.40 and 3.01 GPa.     

High-pressure X-ray diffraction study of dimedone

Abstract

Dimedone (i.e. 5.5-dimethyl-I,3-cyclohexanedione) crystals, C₈HI₁₂O₂, have been studied at high pressures by X-ray diffraction using a Merrill-Bassett diamond-anvil cell. The unit-cell dimensions have been measured to 1.20(5) GPa and the structure has been determined at 0.95(5) GPa. The crystal compressibility is strongly anisotropic and non-linear, relatively strong compressibility of the crystals is observed along the helices of the hydrogen-bonded molecules. Small anomalous changes of the unit-cell dimensions are observed between 0.1 and 50 MPa. The main structural changes are compression of intermolecular contacts, but also an alongation of the O=C bond—accompanied with the compression of the hydrogen bond involving the carbonyl oxygen atom—has been observed. This elongation is consistent with similar effects reported on compression of the hydrogen bonds in 1,3-cyclohexanedione and 2-methyl-1,3-cyclopentanedione. Crystal data for the dimedone structure at 0.95 GPa: monoclinic, P2₁/c, a=9.909(6), b= 6.505(3), c=12.313(6) Å, β=14.51°, V=722.1(5) Å, Z=4, R=0.139 for 336 independent reflections.     

X-ray diffraction study of a sequence of phase transitions in Cs2HgCl4 crystals

The temperature behavior of lattice parameters and diffraction patterns of the reciprocal lattice in Cs₂HgCl₄ crystals is studied by x-ray diffraction in the temperature range from 4.2 to 300 K. A sequence of phase transitions is observed and attributed to the evolution of incommensurate and commensurate modulations along the crystallographic a and c axes of a unit cell in the initial Pnma structure.     

Compressibility of Fe1.087Te: a high pressure X-ray diffraction study

Fe_1.087Te exhibits three phases in the pressure range from ambient to 16.6?GPa and becomes amorphous at higher pressures. All three phases have tetragonal symmetry. The low pressure T-phase is stable in the pressure range 0≤P<4.1?GPa and is found to be relatively soft having zero pressure bulk modulus B ₀=36(1)?GPa. The intermediate cT-phase is less compressible with B ₀=88(5)?GPa and stable in the pressure range 4.1≤P<10?GPa while a more compressible phase was observed between 10 and 16.6?GPa.     

X-ray diffraction on solid solutions with atoms of different sizes

The formula for intensity of diffraction of X-rays on random binary solid solution is derived using the linear model of rigid atoms of different sizes in close-packed arrangement. The shape and position of the peaks of diffuse scattering resulting as the main diffraction effect are influenced by different sizes of atoms. On the other hand, the integrated intensity of the diffuse peaks is practically unaffected by the size effect.     

High-pressure X-ray diffraction study of 1T-TaS2

We present a room temperature high-pressure X-ray diffraction study of the layered compound 1T-TaS₂ up to 20 GPa. This material is known to exhibit a variety of structural phase transitions that are ascribed to the stabilization of charge density wave states. It has been recently shown that at pressures larger than 3 GPa and up to 25 GPa, 1T-TaS₂ becomes superconductor below about 5 K. It was suggested that this superconductivity coexists with different CDW states, an hypothesis that can be tested by X-ray diffraction. Our first results at room temperature show that at around 1.9 GPa, the nearly-commensurate (NCCDW) phase transforms into a phase similar to the high temperature incommensurate phase (ICCDW). Above 9 GPa, we show the existence of another IC phase, still discernable up to 20 GPa despite the pressure-induced crystal damage above 13 GPa. These results are consistent with resistivity measurements, but call for a complete exploration of the P–T phase diagram of 1T-TaS₂.     

X-ray diffraction studies on oxide-superconductors under pressure by a new X-ray detection system

Abstract

A new high pressure x-ray diffraction system has been developed, which consists of a diamond anvil cell, an imaging plate as a detector and an 18 kW rotating anode type generator. By this system we found an anisotropic compression and anomalies in linear compressibility for the Bi-oxide superconductors.     

High pressure X-ray diffraction study of Fe2B

We report the results of a synchrotron based X-ray diffraction study of bct-Fe₂B under quasi-hydrostatic conditions from 0 to 50 GPa. Over this pressure range, no phase change or disproportionation has been observed. A weighted fit of the data to the Birch-Murnaghan equation of state yields a value of the bulk modulus, K, of 164±14 GPa and the first pressure derivative of the bulk modulus, K′, of 4.4±0.5. The compression is found to be anisotropic, with the a-axis being more incompressible than the c-axis.     

High pressure X-ray diffraction study of ReS2

The high-pressure behavior of rhenium disulfide (ReS₂) has been investigated to 51.0 GPa by in situ synchrotron X-ray diffraction in a diamond anvil cell at room temperature. The results demonstrate that the ReS₂ triclinic phase is stable up to 11.3 GPa, at which pressure the ReS₂ transforms to a new high-pressure phase, which is tentatively identified with a hexagonal lattice in space group P6?m2. The high-pressure phase is stable up to the highest pressure in this study (51.0 GPa) and not quenchable upon decompression to ambient pressure. The compressibility of the triclinic phase exhibits anisotropy, meaning that it is more compressive along interlayer directions than intralayer directions, which demonstrates the properties of the weak interlayer van der Waals interactions and the strong intralayer covalent bonds. The largest change in the unit cell angles with increasing pressures is the increase of β, which indicates a rotation of the sulfur atoms around the rhenium atoms during the compression. Fitting the experimental data of the triclinic phase to the third-order Birch-Murnaghan EOS yields a bulk modulus of K_OT=23±4 GPa with its pressure derivative K_OT′= 29±8, and the second-order yields K_OT=49±3 GPa.