Crystal Cell Volume Research Articles

Crystal structure and dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 complex perovskite at microwave frequencies

The crystal structure and microwave dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 (0≤x≤1.0) solid solutions incorporated with 1 wt % CuO were investigated. Pure perovskite phases were formed in the whole composition range, and the crystal space group and unit cell volume of the perovskites were analyzed based on x-ray diffraction patterns. The configuration of octahedral tilting and the B-site ordering phase transition between x=0.9 and 1.0 were unambiguously assigned, respectively, to the corresponding superlattice diffractions. Moreover, the two important fingerprints A1g mode and F2g mode in Raman spectra, associated with the evolution of short range ordering and long range ordering of B-site cations, respectively, were further investigated by employing the full width at half-maximum and their Raman shifts to determine the degree of B-site ordering and the crystal bond strength in the perovskites. The microwave dielectric constants, quality factors, and temperature coefficients of resonant frequency of the solid solutions were elaborately investigated and correlated with their crystal structures. The microscopic structure-related thermal parameters in the solid solution were calculated using the Claussius–Mossotti equation to determine the original contributors in the temperature coefficients. Temperature compensated τf value ceramics could be obtained in the range of 0.3<x<0.5. When sintered at 1400 °C for 2.5 h, a dielectric constant εr of 39.9, a quality factor product of 12 600 GHz, and a τf of −25.3 ppm/°C microwave dielectric ceramic were obtained in 0.5Ca0.61Nd0.26TiO3+0.5Nd(Mg1/2Ti1/2)O3+1 wt % CuO composition.

Synthesis and Structural Study of Sr2CuO3 + δ Superconductor under High Pressure

A single-phase Sr2CuO3 + δ superconductor is synthesized under high temperature and high pressure, in which oxygen atoms only partially occupy the apical sites next to the CuO2 planes and act as hole-dopants. The superconducting transition temperature with Tcmax = 75 K is achieved in the material. Structure analysis from x-ray powder diffraction data show that this material crystallizes into a K2NiF4 structure with tetragonal unit cell of a = 3. 795(3) Å and c = 12. 507(1) Å. Energy-dispersive synchrotron x-ray-diffraction studies at ambient are performed on powder samples of Sr2CuO3 + δ in a diamond-anvil cell at pressure up to 35 GPa. Anisotropic compressibility is found. Pressure-induced isostructural phase transition might exist as revealed by the discontinuous change of crystal cell volume V with pressure.

Density functional study of a ferromagnetic ferroelectricLaMnO3∕BaTiO3superlattice

Using the $\mathrm{GGA}+U$ density functional, we have calculated the lattice constants, atomic positions, magnetization, and ferroelectric polarization of a ${(\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3})}_{4.5}{(\mathrm{Ba}\mathrm{Ti}\mathrm{O})}_{4.5}$ superlattice containing five LaO and $\mathrm{Ti}{\mathrm{O}}_{2}$ planes and four $\mathrm{Mn}{\mathrm{O}}_{2}$ and BaO planes. Although $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3}$ is antiferromagnetic, it is ferromagnetic in the superlattice. An approximation to the ferroelectric polarization, obtained from a comparison of superlattice and bulk crystal atomic displacements and unit cell volumes, is found to agree reasonably well with that obtained from a Berry phase calculation. The electric polarization is polarized along the longer in-plane lattice vector, while the Mn spins, when the spin-orbit interaction and spin noncollinearity are included, have different magnitudes, but all point in essentially the same direction as the electric polarization.

Structure, microstructure, and size dependent catalytic properties of nanostructured ruthenium dioxide

Nanostructured powders of ruthenium dioxide RuO 2 were synthesized via a sol gel route involving acidic solutions with pH varying between 0.4 and 4.5. The RuO 2 nanopowders were characterized by X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM). Rietveld refinement of mean crystal structure was performed on RuO 2 nanopowders and crystallized standard RuO 2 sample. Crystallite sizes measured from X-ray diffraction profiles and TEM analysis varied in the range of 4–10 nm, with a minimum of crystallite dimension for pH=1.5. A good agreement between crystallite sizes calculated from Williamson Hall approach of X-ray data and from direct TEM observations was obtained. The tetragonal crystal cell parameter (a) and cell volumes of nanostructured samples were characterized by values greater than the values of standard RuO 2 sample. In addition, the [Ru–O 6] oxygen octahedrons of rutile structure also depended on crystal size. Catalytic conversion of methane by these RuO 2 nanostructured catalysts was studied as a function of pH, catalytic interaction time, air methane composition, and catalysis temperature, by the way of Fourier transform infrared (FTIR) spectroscopy coupled to homemade catalytic cell. The catalytic efficiency defined as FTIR absorption band intensities I(CO 2) was maximum for sample prepared at pH=1.5, and mainly correlated to crystallite dimensions. No significant catalytic effect was observed from sintered RuO 2 samples.

17O quadrupole coupling and the origin of ferroelectricity in isotopically enrichedBaTiO3 and SrTiO3

The 17O electric field gradient (EFG) and chemical shift tensors have been determinedin the paraelectric and ferroelectric phases of isotopically enrichedBaTiO3 andSrTiO3 singlecrystals via 17O NMR. This is the first determination of the17O EFG and chemical shift tensors in any oxide perovskite crystal. The difference in the17O chemicalshifts between BaTiO3 and SrTiO3 is relatively small, whereas there is a large difference in the17O EFGtensors even in the cubic phases. Density functional theory calculations indicate that the difference inthe 17O EFGs is due to a crystal cell volume effect together with effects due to the difference in ionic radii ofBa and Sr that result in a larger distortion of the nearly spherical charge distribution around the oxygenin BaTiO3.

Microstructure, electrical and ethanol-sensing properties of perovskite-type SmFe0.7Co0.3O3

Ultrafine SmFe 0.7 Co 0.3 O 3 powder, prepared by a sol–gel method, shows a single-phase orthogonal perovskite structure. The influence of annealing temperature upon its crystal cell volume, microstructure, electrical and ethanol-sensing properties was investigated in detail. When the annealing temperature increases from 600 to 950 °C, the unit cell volume of the SmFe 0.7 Co 0.3 O 3 sample reduces, and its average grain size increases. When the annealing temperature increases from 600 to 850 °C, the optimal working temperature and response to ethanol of the SmFe 0.7 Co 0.3 O 3 sensor increase, and the response–recovery time shortens. But when the annealing temperature further increases from 850 to 950 °C, there are decreases of the optimal working temperature and sensor response, and the response–recovery time is prolonged. The results indicate that, as for sensor response, its optimal annealing temperature is about 850 °C, and the sensor based on SmFe 0.7 Co 0.3 O 3 annealed at 850 °C shows the highest response S = 80.8 to 300 ppm ethanol gas, and it has the best response–recovery and selectivity characteristics. When the ethanol concentration is as low as 500 ppm, the curve of its optimal response versus concentration is nearly linear. Meanwhile, the influence mechanisms of annealing temperature upon the conductance, the optimal working temperature and sensor response for SmFe 0.7 Co 0.3 O 3 were studied.

Influence of Zr concentration on crystalline structure and its electronic properties in the new [formula omitted] compound in wurtzite phase: An ab initio study

In the present work, we have calculated the structural and electronic properties of the new ZrxAl1-xN compound in wurtzite phase for x=0.25, 0.50 and 0.75. The study is based on density functional theory (DFT) with augmented plane wave plus local orbitals method for calculating crystal properties (FP-LAPW). Based on the graphs of the energy versus the crystal unitary cell volume for each x, we concluded that the structural properties vary with x. Special analysis is made on the bond lengths Zr–N and Al–N. And based on the relations of dispersion, we see that the electronic properties vary substantially with x. A remarkable fact is that we predict a possible semiconductor–metal transition for any x⩽0.25.

Reaction Mechanism Based on X-ray Crystal Structure Analysis during the Solid-State Polymerization of Muconic Esters

We have investigated a change in the crystal structures of di(4-alkoxybenzyl) (E,E)- and (Z,Z)-muconates during the solid-state polymerization by X-ray crystal structure analyses and have discussed a reaction mechanism for the polymerization. The solid-state polymerization is divided into a homogeneous polymerization which proceeds in the solid solution of the remaining monomer and the resulting polymer and a heterogeneous polymerization in which a crystal phase separation occurs between the monomer and polymer crystal domains during the reaction. According to the former model, the monomer crystal phase continuously changes into the polymer crystal phase without any phase separation when the slightest movement of atoms induces less strain in the crystals. The molecular dynamics of the muconates in the solid state were monitored by in situ single and powder X-ray diffraction experiments. In fact, we succeeded in the direct observation of the expanding crystal lattices and cell volume at the initial stage of polymerization, followed by subsequent shrinking in the process of the homogeneous reaction. On the other hand, a phase separation was observed during the reaction according to the heterogeneous polymerization model, in which a considerable movement of atoms is required. The monomer stacking structure determines the reaction path during the solid-state polymerization.

A-site deficiency, phase purity and crystal structure in lanthanum strontium ferrite powders

Lanthanum strontium ferrite (LSF) powders of average composition of (La 1− x′ Sr x′ ) y′ FeO 3+ δ , were fabricated over a range of average strontium composition between 0.2 ≤ x′ ≤ 0.5 and average A-site occupancy between 0.8 ≤ y′ ≤ 1.0. Samples that were originally determined to be perovskite phase pure using X-ray diffraction with CuK α radiation were found to have significant amounts of non-perovskite phases when evaluated using high-energy synchrotron radiation. As-fabricated samples with nominal A-site deficiency, y′ < 1, contained a hexaferrite phase. When treated at 955 °C in pO 2 = 10 − 10 atm, those samples contained magnetite. The actual composition of the perovskite phase was corrected to account for the presence of the second phases through mass balance calculations. As a result, the actual A-site deficiency of the perovskite phase was much lower than the average value of the bulk powder. For as-fabricated powders with x′ < 0.4, it was determined that the A-site deficient LSF perovskite phases were metastable. At equilibrium, a mixture of A-site stoichiometric perovskite and hexaferrite phases was present. The refined perovskite crystal structures and unit cell volumes were consistent with literature trends.

SINGLE CRYSTAL NEUTRON DIFFRACTION FOR THE INORGANIC CHEMIST – A PRACTICAL GUIDE

Advances and upgrades in neutron sources and instrumentation are poised to make neutron diffraction more accessible to inorganic chemists than ever before. These improvements will pave the way for single crystal investigations that currently may be difficult, for example due to small crystal size or large unit cell volume. This article aims to highlight what can presently be achieved in neutron diffraction and looks forward toward future applications of neutron scattering in inorganic chemistry.

Superconductivity and the disorder effect in Ag and Al double doped MgB2

A series of polycrystalline bulk samples of Mg1−2x(AgAl)xB2 (0.0%⩽x⩽1.0%) has been synthesized by a solid state reaction method. The structure, Raman spectrum, and superconducting properties have been investigated by x-ray diffraction, Raman spectroscopy, and low-temperature resistivity measurements. It is found that the Ag, Al double doping causes the expansion of crystal lattice along the a- and c-axis orientations due to the substitution inducing ionic size variation. A redshift of peak position is observed in Raman spectra, which is ascribed to the crystal cell volume change inducing the variation of the phonon frequency. The superconducting transition temperature (Tc) is degressive with the doping level (x) increase. By the Ag and Al double doping, the hole concentration is kept to be unchanged in MgB2, which eliminates the effects of the charge carrier concentration change and band filling on Tc. It is suggested that the reason of the Tc suppression caused by the double doping is the co-operating results of the disorder effect and the chemical pressure effect induced by the chemical substitution.

Influence of V content on structure and hydrogen desorption performance of TiCrV-based hydrogen storage alloys

The influence of V content on structure and hydrogen desorption performance of TiCr1.8−XVX alloys were investigated by X-ray diffraction (XRD), pressure composition temperature (PCT) and thermogravimetry and differential scanning calorimetry (TG–DSC) tests. XRD tests showed that the crystal cell volume of both the as-cast and hydrogenated alloys increased with increasing V content. At the same time, however, their hydrogen desorption content first increased and then decreased. Hydrogen desorption tests showed that alloy TiCr1.0V0.8 had the highest hydrogen desorption content among all the investigated alloys.

X-ray Studies of the (La,Sr)MnO[sub 3] Perovskite Manganite Structure

X-ray studies of perovskite manganites (La0.9Sr0.1)0.9MnO3 and La1−x SrxMnO3 (x = 0.1, 0.15, 0.2, 0.25) are reported. The atom positions and interatomic distances and angles are calculated as a function of Sr doping at room temperature using the FullProf software. The temperature dependences of the crystal lattice parameters and unit cell volume are investigated. The effects of structural and magnetic phase transitions on the crystal lattice parameters are studied in detail. The bulk magnetoelastic contribution to thermal expansion is studied experimentally and calculated.

The sulfur oxygenase reductase from Acidianus ambivalens is an icosatetramer as shown by crystallization and Patterson analysis

The sulfur oxygenase reductase (SOR) is the initial enzyme in the aerobic sulfur metabolism of the thermoacidophilic and chemolithoautotrophic crenarchaeote Acidianus ambivalens. Single colorless polyhedral crystals were obtained under two crystallization conditions from SOR preparations heterologously overproduced in Escherichia coli. They belonged to space-group I4 and diffraction data were collected up to 1.7 Å resolution. Their Patterson symmetry shows additional 4-, 3- and 2-fold non-crystallographic symmetry rotation axes, characteristic of the point group 432. Taking into account the molecular mass of SOR, the crystal unit cell volume, the non-crystallographic symmetry operators and previous electron microscopy studies of the SOR, it was deduced that the quaternary structure of the functionally active enzyme is an icosatetramer with 871 kDa molecular mass.

Microstructure and high-temperature electrochemical characteristics of Zr 0.9Ti 0.1Ni 1.0Mn 0.7V 0.3Si x ( x = 0.05, 0.10, 0.15, 0.20) alloy

The crystal structure, the phase composition and electrochemical characteristics of non-stoichiometric Zr 0.9Ti 0.1Ni 1.0Mn 0.7V 0.3Si x ( x=0.05, 0.10, 0.15, 0.20) alloys under high temperature were investigated by means of XRD, SEM, EDS and electrochemical measurements. It was shown that Si addition greatly improved high-temperature electrochemical characteristics of the AB 2 Laves phase alloys. At 338 K, the discharge capacity of Zr 0.9Ti 0.1Ni 1.0Mn 0.7V 0.3Si 0.10 alloy reached 249 mAh g −1, and the charge retention was 94.20% for 24 h, and the capacity retention for 300 charge/discharge cycles was 45.17%. The improvement in the high-temperature electrochemical characteristics of the alloy was attributed to the formation of the Zr-rich second phase in the matrix and the increasing stability of AB 2-type Laves phase alloy hydride due to Si addition in alloy. They seem to be also related with the formation of a compact silicon oxide film on the alloy surface, which increases the corrosion resistance performance of the alloy in KOH solution. At high temperature, the main cause of further decreasing of alloy cycle stability may be due to the corrosion and the oxidising deteriorate on alloy surface, and the expansion ratio of crystal cell volume probably is not a critical effect on the cycle stability of alloy.

Structural and Transport Properties for Al- and Fe-DopingLa0.67Ca0.33MnO3 Perovskite Manganese

The effects of Al and Fe ion doping in Mn sites wasstudied for the colossal La0.67Ca0.33MnO3magnetoresistance material. It was found that when the Fe-dopingamount x increases, the crystal cell structure has no obviouschange, but the crystal cell volume decrease monotonically forAl-doping. Both resistances increase rapidly and the insulator–metaltransition temperature moves to lower temperature and decreaseslinearly with Al-doping. The area for Al-doping is broader than Fe. Atsmall amount of Al-doping, the resistance satisfies the metal transportproperty when T<TIM. The characteristic ofthe transport behaviour for Al- and Fe-doping can be explained byterminating the double exchange channel of Mn3+–O2−–Mn4+.

Effect of Heat Treatment on Properties of Ti-Mn Based Laves Phase Hydrogen Storage Alloys

AbstractEffect of heat treatment on the properties and microstructure of non-stoichiometric Ti-Mn based hydrogen storage alloys were investigated. The results were presented that the hydrogen storage capacity was increased and the width of P-C-T Plateau extended, but the slope of plateau increased after heat treatment. Through SEM, EDS and XRD analysis, it was found that the crystal parameters and cell volume was increased, meanwhile the composition homogeneity effectively enhanced and the content of C15 phase decreased after heat treatment. The accretion of slope of plateau would be related to the ratio of valence electron/atom of the alloys.

The Structure of Mast Cell Secretory Granules in the Blind Mole Rat (Spalax ehrenbergi)

Eosinophils, basophils, and mast cells produce and secrete active substances whose role is to attack invading parasites and protect the host. In this study we use morphometric methods to study mast cells in the blind mole rat (Spalax ehrenbergi). The subterranean and solitary way of life of this species has led to the evolutionary development of special anatomical, morphological, behavioral, and physiological adaptations. Because of its particular lifestyle, the mole rat is less exposed to parasites than other rodents. This could provide a unique model for research into the pathobiology of mast cells. The paracrystalline structure of the mast cell granule content is composed of parallel plates. Diffraction analysis of electron micrographs of thin sections of araldite-embedded tissues indicated that each crystal line plate is a periodic array of parallelograms. The crystal unit cell volume is approximately 930 nm3, suggesting that each unit cell is composed of one heparin molecule and one to three additional adsorbed proteins. Morphometric data show that characteristics of the secretory granules of mast cells of the blind mole rat resemble those of other rodents. The mast cell unit granule volume in the present study was calculated to be 0.055 μm3, similar to that of rat peritoneal mast cells.

Ab initiomethane dimer intermolecular potentials

Two purely ab initio non-bonded potential functions for methane dimer interactions in the MM3 framework have been established. The parameter fitting was performed to 130 carefully selected configurations. Intermolecular energies and forces have been evaluated at the second-order Møller-Plesset perturbation theory level (MP2) with a medium size basis set. Since the resultant energies were found to be too shallow, an empirical correction procedure to the existing MP2 potential energy surface (PES) was carried out to obtain MP2 energies in a very large basis set. The first of the two emerging parameter sets was obtained by fitting to MP2 forces, while the second is based on the corrected MP2 PES. Both resultant potentials predicted reasonable agreement with experimental properties, which included methane and butane virial coefficients, liquid methane and butane densities and heats of vaporization, liquid methane C-C radial distribution functions, crystal unit cell volumes, and heat of sublimation data. The role of more sophisticated potential functions has also been examined.

Local-density-derived semiempirical pseudopotentials.

Transferable screened atomic pseudopotentials were developed 30 years ago in the context of the empirical pseudopotential method (EPM) by adjusting the potential to reproduce observed bulk electronic energies. While extremely useful, such potentials were not constrained to reproduce wave functions and related quantities, nor was there a systematic way to assure transferability to different crystal structures and coordination numbers. Yet, there is a significant contemporary demand for accurate screened pseudopotentials in the context of electronic structure theory of nanostructures, where local-density-approximation (LDA) approaches are both too costly and insufficiently accurate, while effective-mass band approaches are inapplicable when the structures are too small. We can now improve upon the traditional EPM by a two-step process: First, we invert a set of self-consistently determined screened LDA potentials for a range of bulk crystal structures and unit cell volumes, thus determining spherically symmetric and structurally averaged atomic potentials (SLDA). These potentials reproduce the LDA band structure to better than 0.1 eV, over a range of crystal structures and cell volumes. Second, we adjust the SLDA to reproduce observed excitation energies. We find that the adjustment represents a reasonably small perturbation over the SLDA potential, so that the ensuing fitted potential still reproduces a &gt;99.9% overlap with the original LDA pseudowave functions despite the excitation energies being distinctly non-LDA. We apply the method to Si and CdSe in a range of crystal structures, finding excellent agreement with the experimentally determined band energies, optical spectra ${\mathrm{\ensuremath{\epsilon}}}_{2}$(E), static dielectric constants, deformation potentials, and, at the same time, LDA-quality wave functions.