Energy Dispersive X-ray Powder Diffraction Research Articles

Phase Changes in Ge Nanoparticles

Butyl-capped crystalline germanium (Ge) nanoparticles were synthesized at room temperature in dimethoxyethane by reduction of GeCl4 with Na(naphthalide) and subsequent reaction with butyl Grignard. The nanoparticles were isolated in hexane and characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), elemental analysis, and X-ray powder diffraction (XRD). The product from this room-temperature reaction was heated under vacuum at temperatures of 200−600 °C at 50 °C intervals. The product obtained from the 300 °C treatment was soluble in hexane, while the products from temperatures greater than 300 °C were not. SAED was consistent with crystalline Ge from the initial synthesis at room temperature and amorphous Ge for the product heated under vacuum to 300 °C. X-ray powder diffraction of the 300 °C product shows the transition from amorphous to crystalline nanoparticles occurring between 550 and 600 °C. TEM shows that the nanoparticles remain dispersed and nonaggregated up to 600 °C. Differential scanning calorimetry (DSC) shows a crystallization exotherm at 561 °C and a melting endotherm at 925 °C for nanoparticles with average diameter of 8 nm.

Equation of state of aluminum silicon carbide α-Al 4SiC 4

Quasi-hydrostatic compression of aluminum silicon carbide, α-Al 4SiC 4, has been studied up to 6 GPa at room temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit of the experimental p– V data to the Birch equation of state yields the values of the bulk modulus, B 0, of 182(10) GPa with fixed first pressure derivative of the bulk modulus, B′ 0, of 4.0. The compression is found to be anisotropic with higher compressibility along c-axis.

Equation of state of aluminum carbide Al 4C 3

Quasi-hydrostatic compression of aluminum carbide, Al 4C 3 has been studied to 6 GPa at room temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit of the experimental p– V data to the Birch equation of state yields the values of the bulk modulus, B 0, of 130(5) GPa and the first pressure derivative of the bulk modulus, B′ 0, of 4.6(9). The compression is found to be anisotropic, with the a-axis being more compressible than the c-axis.

Equation of state of silicon nitride carbodiimide Si 2CN 4

The lattice parameters of silicon nitride carbodiimide Si 2CN 4 have been measured up to 8 GPa at room temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit of the experimental p– V data to the Birch–Murnaghan equation of state yields the values of the bulk modulus of 8.8(2) GPa and its first pressure derivative of 3.4(1). The compression is found to be anisotropic, with the b-axis being significantly more compressible than the a-and c-axes.

Al2O3-Coated Honeycomb Cordierite-Supported CuO for Simultaneous SO2 and NO Removal from Flue Gas: Effect of Na2O Additive

Effect of Na2O additive in an Al2O3-coated cordierite honeycomb ceramic-supported CuO catalyst on simultaneous SO2 and NO removal activities was studied at 400 °C. Results show that SO2 removal activity increases with increasing sodium loading from 0 to 2.0 wt % but decreases with further increasing sodium loading to 3.0 wt %, while NO removal activity monotonically decreases with increasing sodium loading, from 99 to 65%, due to increased NH3 oxidation activity. Mechanism of the effect of Na2O additive on SO2 removal activity is studied using N2 adsorption, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray powder diffraction (XRD). Results show that Na2O additive (at sodium loadings of 1.0−2.0 wt %) inhibits the formation of Al−Si−O species and improves the distribution of CuO, which limits pore plugging and increases BET surface area of the catalyst. These behaviors account for the promoting effect of Na2O additive on SO2 removal activity. However, with increasing sodium loadi...

A time resolved, in-situ X-ray diffraction study of the de-intercalation of anions and lithium cations from [LiAl2(OH)6]nX·qH2O (X = Cl−, Br−, NO3−, SO42−)

The layered double hydroxides (LDHs), [LiAl2(OH)6]nX·qH2O (Xn− = Cl−, Br−, NO3−, SO42−) spontaneously lose both Li+ cations and Xn− anions to give crystalline Al(OH)3 on stirring in water. The kinetics of this topochemical de-intercalation reaction have been studied using time-resolved, in-situ energy dispersive X-ray powder diffraction. The temperature dependence of the rate of the de-intercalation reaction yields activation energies of 94 ± 15 kJ mol−1 for mono-dispersed [LiAl2(OH)6]Cl·1.5H2O crystallites (particle size 5–10 µm) and 117 ± 15 kJ mol−1 for poly-dispersed [LiAl2(OH)6]Cl·1.5H2O crystallites (particle size 1–30 µm). The rate of ion de-intercalation was found to decrease as the H2O/LDH ratio decreased. The rate of the de-intercalation has also been shown to be dependent on the interlayer anion, with the reaction rates NO3− > Cl − > Br−. In the case of SO42− rapid de-intercalation only goes to 40% completion.

Equation of state and phase stability of turbostratic carbon nitride

The lattice parameters of turbostratic carbon nitride (t-CN) have been measured to 20 GPa at room temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit to the experimental p– V data using Birch–Murnaghan equation of state gives values of the t-CN bulk modulus 20.1(5) GPa and its pressure derivative 8.3(2). These values point to a significantly higher compressibility of turbostratic carbon nitride as compared to turbostratic graphite. In the 4.7–17.8 GPa range the onset temperature of t-CN decomposition increases from 990(10) to 1850(50) K. The decomposition results in the formation of disordered graphite at pressure below 8 GPa, and diamond at higher pressures.

Synthesis of well-aligned boron nanowires and their structural stability under highpressure

Owing to its unusual bonding and vast variety of unique crystal structures, boronis one of the most fascinating elements in the periodic table. Here we report thelarge-scale synthesis of well-ordered boron nanowires and their structural stabilityat high pressure. Boron nanowires with uniform diameter and length grownvertically on silicon substrates were synthesized by radio-frequency magnetronsputtering with a target of pure boron using argon as the sputtering atmospherewithout involvement of templates and catalysts. Detailed characterization byhigh-resolution transmission electron microscopy and electron diffraction indicatesthat the boron nanowires are amorphous. Structural stability of the boronnanowires at room temperature has been investigated by means of in situhigh-pressure energy-dispersive x-ray powder diffraction using synchrotronradiation in a diamond anvil cell. No crystallization was observed upto a pressure of 103.5 GPa, suggesting that the amorphous structure ofboron nanowires is stable under high pressure at ambient temperature.

Elastic Moduli and Hardness of Cubic Silicon Nitride

The bulk modulus B0= 290(5) GPa and its first pressure derivative B′0= 4.9(6) were obtained for c‐Si3N4 from volume versus pressure dependence. Measurements were performed under quasi‐hydrostatic conditions in a diamond anvil cell to 53 GPa using synchrotron radiation and energy dispersive X‐ray powder diffraction. This combined with nanoindentation measurements determined the shear modulus G0 of c‐Si3N4 to be 148(16) GPa. The Vickers microhardness HV(0.5) for dense, oxygen‐free c‐Si3N4 was estimated to be between 30 and 43 GPa. Both the elastic moduli and microhardness of c‐Si3N4 exceed those of the hexagonal counterparts, α‐ and β‐phases.

The site occupancy of Mg in the brownmillerite structure and its effect on hydration properties: an X-ray/neutron diffraction and EXAFS study

Samples of pure (Ca2FeAlO5) and lightly doped (Ca2Fe0.95Al0.95Mg0.05Si0.05O5) brownmillerite have been synthesized. Synchrotron X-ray and neutron diffraction data have been collected so that the structures can be refined using, simultaneously, both diffraction data sets and known compositional information; this overcomes the problem of under-determinacy resulting from multi-occupation of the tetrahedrally and octahedrally coordinated sites in the structure. For the pure form, a 2.7:1 iron/aluminium preference for octahedral/tetrahedral (respectively) occupation is obtained. This trend is reflected also in the doped brownmillerite, though, because of the low level of Mg doping, the occupancy of Mg is only resolved through the additional use of Mg EXAFS (extended X-ray absorption fine structure) data, which shows that Mg displays a distinct octahedral site preference rather than a disordered occupation between the octahedral/tetrahedral sites. The consequences of Mg doping are then examined using time-resolved multi-angle energy-dispersive powder X-ray diffraction studies of the mineral undergoing hydration; this shows that the pure form is more active than the doped form.

磁性材料 ＣａＦｅＯ３の高圧下単結晶育成

Single crystals of CaFeO3 have been synthesized at high pressure of 4.5 GPa with a mixture of KClO4, NaCI and CaCl2 as flux and oxidizing agent. The temperature dependence of the resistivity showed a metal-insurating transition at 295 K, corresponding to the charege disproprotionation. A screw-spin type antiferromagnetic transition was observed at 115 K. These results indicated that the crystals were free from oxygen defect. Energy-dispersive powder X-ray diffraction study with synchrotron radiation at high pressure revealed that a moisture was necessary to crystal growth of CaFeO3.

Equations of state of MgO at high pressure and temperature

A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.

Time-resolved, in situ X-ray diffraction studies of intercalation in lamellar hosts

Energy dispersive X-ray diffraction (EDXRD) has been used to perform in situ kinetic studies on the intercalation of a range of guest molecules in layered lattices. The kinetics of the intercalation of cations (K +, PyH + (Py=C 5H 5N), NMe 4 +) and the long chain ammonium ions C 12TMA, C 16TMA, C 18TMA (C 12TMA=dodecyltrimethylammonium, C 16TMA=hexadecyltrimethylammonium and C 18TMA=octadecyltrimethylammonium) into crystals of MnPS 3 have been determined. These reactions are very fast, and in some cases novel transient phases are observed. The rate of cobaltocene, Co(η-C 5H 5) 2, intercalation in layered metal dichalcogenides ZrS 2, 2H-SnS 2, 2H-SnSe 2, 2H-TaS 2, 2H-NbS 2, 1T-TaS 2 and TiS 2 has also been investigated. Integrated intensities of the Bragg reflections have been used to determine the extent of reaction ( α) versus time for each of these reactions. A number of kinetic models have been considered, including the Avrami–Erofeyev ( m=1.5) deceleratory nuclei-growth model and statistical simulation. The concentration and solvent dependence of the rate of Co(η-C 5H 5) 2 intercalation into 2H-SnS 2 has also been determined. Surprisingly, we find that the rate of intercalation is invariant to the initial Co(η-C 5H 5) 2 concentration over a wide concentration range. The rate of intercalation of the lithium salts (LiX; X=Cl, Br, NO 3 and OH) into Gibbsite (γ-Al(OH) 3) giving the layered double hydroxides [LiAl 2(OH) 6]X· nH 2O (X=Cl, Br, NO 3 and OH) and [LiAl 2(OH) 6] 2SO 4· nH 2O has been studied. The temperature dependence of the rate of intercalation of LiCl yields an activation energy of 27 kJ mol −1. The reaction was also found to be half order with respect to the initial concentration of LiCl. Time-resolved in situ energy dispersive X-ray powder diffraction (EDXRD) spectra have been recorded following the addition of an aqueous solution of hexadecyltrimethylammonium chloride (C 16H 33N +Me 3Cl −=C 16TMACl) to kanemite (NaHSi 2O 5·3H 2O). The diffraction data suggest that initially a layered phase forms due to intercalation of the alkylammonium ions which then transforms into a silicate-organic mesophase which is the precursor to the hexagonal mesoporous silicate, FSM-16.

Determination of the kinetics of crystallisation of gibbsite using time resolved in situ energy dispersive powder X-ray diffraction

Time resolved in situ powder X-ray diffraction has been used to study the kinetics of crystallisation of gibbsite from supersaturated synthetic Bayer liquors as a function of temperature and hydroxide ion concentration. It was found that the crystallisation data was best described in terms of the Avrami–Erofe’ev kinetic model. This analysis indicated a two-dimensional growth mechanism with a deceleratory nucleation rate.

Effects of isostatic oxygen pressure on the crystal growth and optical properties of undoped and Er3+-doped Ca3(VO4)2 single-crystal Fibres

The influence of the isostatic oxygen pressure as a crystal growth atmosphere on the optical and structural properties of undoped and erbium-doped calcium orthovanadate single-crystal fibres was studied by optical absorption, photoluminescence, energy-dispersive X-ray analysis and X-ray powder diffraction techniques. Relationships between the oxygen pressure used during the crystal growth and some optical and structural parameters are established. Through an oxygen vacancy model the effects of the crystal growth conditions on the physical properties of the material are inferred. Copyright © 2000 John Wiley & Sons, Ltd.

On the Peak Profiles in Energy-Dispersive Powder X-ray Diffraction with Synchrotron Radiation

The peak profiles of standard reference materials have been investigated with energy-dispersive X-ray diffraction at a synchrotron source. Keeping the detector dead time below 2%, the peak profiles were essentially pure Gaussians independent of energy in the range investigated. Plastic deformation of ductile f.c.c.-based materials (Cu3Au and Au) leads to increased Lorentzian contributions to the peak profiles. A single-line profile analysis was performed to obtain estimates of size and strain; reasonable values were found.

Effect of pressure on structural properties of intermetallic LnM lanthanide compounds

Energy dispersive powder X-ray diffraction measurements with diamond anvil high pressure cells at ambient temperature and pressure up to 50 GPa on the LnM compounds GdCu, LaAg, NdAg, NdZn, CeZn and LaZn show systematically high pressure phase transformations from the cP2 (CsCl-type) structure to lower symmetry phases, however, with only minor effects from valence instabilities.

X-ray diffraction study of BaLu2CuO5 and BaNd2CuO5 at high pressures

The volume compression of BaNd2CuO5 (brown phase) and BaLu2CuO5 (green phase) have been measured to 8.67 and 9.23 GPa, respectively, utilizing a diamond anvil high-pressure cell and energy dispersive X-ray powder diffraction. The pressure dependence of the volume of the orthorhombic BaLu2CuO5 and tetragonal BaNd2CuO5 unit cell, as determined by a least-squares fit of the data, are both linear and follow the equations of V=−1.615P+260.62 Å3, and V=−1.9001P+476.92 Å3, respectively. While linear compressions of the unit cell parameters of BaNd2CuO5 exhibit isotropic compressive behavior within our experimental error, BaLu2CuO5 shows somewhat anisotropic compressibility behavior. From the observed data, the bulk modulus of BaNd2CuO5 is determined to be 161±8 GPa and the Young's modulus is estimated to be 193 ±9 GPa. For BaLu2CuO5, the corresponding bulk modulus and the Young's modulus are estimated to be 251±13 GPa and 301±16 GPa, which are significantly greater than those of the brown phase and the high-Tc superconductor Ba2YCu3O6+x. No evidence of a pressure-induced phase transformation was found in either compound in the pressure range studied.

Pressure-induced structural phase transitions in theAMnF4series (A=Cs, Rb, K) studied by synchrotron x-ray powder diffraction: Correlation between hydrostatic and chemical pressure

The effect of applying hydrostatic pressure in the layered-perovskite A${\mathrm{MnF}}_{4}$ (A=Cs, Rb, K) series has been studied using energy-dispersive synchrotron x-ray powder diffraction at pressures between ambient and 20 GPa. At ambient pressure ${\mathrm{CsMnF}}_{4}$ is tetragonal with space group P4/n, ${\mathrm{RbMnF}}_{4}$ is orthorhombic with space group Pmab and ${\mathrm{KMnF}}_{4}$ is monoclinic with space group P${2}_{1}$/a. ${\mathrm{CsMnF}}_{4}$ was found to undergo a first-order structural phase transition, from tetragonal to orthorhombic symmetry at ${\mathit{P}}_{{\mathit{c}}_{1}}$=1.4\ifmmode\pm\else\textpm\fi{}0.2 GPa. At pressures in excess of ${\mathit{P}}_{{\mathit{c}}_{2}}$=6.3\ifmmode\pm\else\textpm\fi{}1 GPa, for the Cs derivative, and ${\mathit{P}}_{{\mathit{c}}_{3}}$=4.5\ifmmode\pm\else\textpm\fi{}1 GPa, for the Rb derivative, the symmetry appears to be monoclinic. Moreover, the critical unit-cell volumes associated with ${\mathit{P}}_{{\mathit{c}}_{1}}$, ${\mathit{P}}_{{\mathit{c}}_{2}}$, and ${\mathit{P}}_{{\mathit{c}}_{3}}$ are slightly higher than the ambient pressure unit-cell volumes of ${\mathrm{RbMnF}}_{4}$ for ${\mathit{P}}_{{\mathit{c}}_{1}}$ and ${\mathrm{KMnF}}_{4}$ for ${\mathit{P}}_{{\mathit{c}}_{2}}$ and ${\mathit{P}}_{{\mathit{c}}_{3}}$. Hydrostatic pressure has been found to have a similar effect on the crystal symmetry of the series as the decreasing of the radius of the alkaline ion from Cs to Rb and K. A correlation between hydrostatic and chemical pressure can therefore be established from the structural point of view for the A${\mathrm{MnF}}_{4}$ series. The tetragonal to orthorhombic transition of ${\mathrm{CsMnF}}_{4}$ has been found to be inhibited when NaCl is used as an internal pressure calibrant. The partial substitution of Cs by Na in ${\mathrm{CsMnF}}_{4}$ at ${\mathit{P}}_{{\mathit{c}}_{1}}$ has been shown to be a likely explanation for this behavior. The anisotropic broadening of the Bragg peaks for pressures higher than ${\mathit{P}}_{{\mathit{c}}_{1}}$ has been analyzed in terms of microstrain affecting the ${\mathrm{CsMnF}}_{4}$ lattice due to Na incorporation. A substitutional reaction has been shown to be a competitive process, versus a structural phase transition, that enables the system to return to equilibrium after applying pressure on it. Finally, the equation of state associated with the different high-pressure phases has been calculated including compressibilities. \textcopyright{} 1996 The American Physical Society.

Melting and premelting of silicates: Raman spectroscopy and X-ray diffraction of Li2SiO3 and Na2SiO3

The isostructural lithium (Li2SiO3) and sodium (Na2SiO3) metasilicates have been investigated from room temperature up to the melting point by single-crystal Raman spectroscopy and energy-dispersive X-ray powder diffraction. The unit-cell parameters and Raman frequencies of Li2SiO3 vary regularly with temperature up to the melting point, which is consistent with the lack of premelting effects in calorimetric measurements. In contrast, Na2SiO3 undergoes a transition at about 850 K from orthorhombic Cmc 21 symmetry, to a lower symmetry (possibly Pmc 21), and shows near 1200 K changes in the Raman spectra that correlate well with the premelting effects as determined from calorimetry observations. In both compounds, a high alkali mobility likely sets in several hundreds of degrees below the melting point. Premelting in Na2SiO3 is associated with extensive deformation of the silicate chains as evidenced near the melting point by similarities in the Raman spectra of the crystalline and liquid phases.