X-ray Rietveld Analysis Research Articles

Optical, mechanical and electrical properties of LSCF–SDC composite cathode prepared by sol–gel assisted rotary evaporation technique

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is a perovskite-type oxide that exhibits excellent mixed ionic–electronic conducting properties and is a suitable cathode material for intermediate temperature solid oxide fuel cells. This study investigates the microstructural, optical, mechanical, and electrical properties of an LSCF–samarium-doped ceria (SDC) composite cathode. LSCF–SDC composite cathode powders were prepared by mixing 50 wt% SDC electrolyte with LSCF cathode powders obtained by the rotary evaporation technique. The band gap of the prepared powders was determined via diffuse reflectance UV–visible spectroscopy. The chemical composition, mechanical properties, and electrochemical properties of the sintered pellets were characterized using Raman spectroscopy, Vickers hardness, and impedance spectroscopy, respectively. X-ray diffraction and Rietveld analysis showed that phase purity was only 96%. Moreover, a small fraction of tetragonal phase impurity was observed on the LSCF powders. Impurities significantly affected the phase stability and microstructure of the LSCF–SDC composite cathode. The addition of the SDC electrolyte enhanced the densification of the composite cathode, thereby improving mechanical properties. However, the addition of SDC exerted different effects on the DC electrical conductivity and area-specific resistance (ASR) of the composite cathode. At 800 °C, the ASR value of the LSCF was only 2% that of the LSCF–SDC composite cathode. Overall, the electrical properties of the LSCF–SDC composite cathode are closely related to the crystal structure, purity, and microstructure of LSCF cathode powders.

Effect of boron content on structure and magnetic properties in CoFe2O4 spinel nanocrystals

We study the effect of boron content on the structural and magnetic properties of CoFe2O4 spinel nanocrystallines synthesized by sol-gel method. The crystal structure and phase identification of samples are studied by using X-ray diffraction experiment and Rietveld analysis. Rietveld refinement results reveal that all samples have cubic symmetry with space group Fd3m. The cationic distributions are obtained from Rietveld refinement that boron ions are settled into both tetrahedral and octahedral sites in spinel lattice. The crystallite sizes of samples are found in a range of 47–67 nm that is in the limit of single domain in such structure. All samples show ferromagnetic nature and magnetic transition was not seen in the temperature range of 5–400 K. The magnetic domains are pinned with adding boron ions into the CoFe2O4 spinel structure at low temperatures. Thus, an increment in the propagation field (Hp) and temperature (Tp) by boron content in CoFe2O4 structure is observed. In addition, the saturation magnetization (Ms) normalized by crystal size increases with increasing boron concentration. The temperature dependence of magnetic properties of the samples taken by experimental data are confirmed with the Neel-Arhenius model by adding thermal dependence of magnetocrystalline anisotropy term. The results indicate that boron-doping into the spinel structure enhances ferromagnetic coupling and suppresses super-exchange interaction between tetrahedral (X) and octahedral (Y) sites.

Structural properties of barium stannate

BaSnO3 has attracted attention as a transparent conducting oxide with high room temperature carrier mobility. We report a series of measurements that were carried out to assess the structure of BaSnO3 over a variety of length scales. Measurements included single crystal neutron and x-ray diffraction, Rietveld and pair distribution analysis of neutron powder diffraction, Raman scattering, and high-pressure x-ray diffraction. Results from the various diffraction probes indicate that both the long-range and local structures are consistent with the cubic symmetry. The diffraction data under pressure was consistent with a robustly cubic phase up to 48.9 GPa, which is supported by density functional calculations. Additionally, transverse phonon velocities were determined from measured dispersion of the transverse acoustic phonon branches, the results of which are in good agreement with previous theoretical estimates and ultrasound measurements.

Effect of synthesis conditions on structural, morphological and luminescence properties of MgAl2O4:Eu3+ nanopowders

Nanocrystalline aluminium magnesium spinel doped with europium ions powders were synthesized via modified Pechini method. The effect of synthesis conditions (calcination temperature and duration) on structural, morphological and luminescence properties of obtained nanopowders was studied. Both X-ray diffraction and Rietveld analysis showed that samples consist of only one crystalline phase – face-centred cubic spinel. The SEM and SLS analysis demonstrated that average particle size is about 50nm. It was shown that the solubility limit of europium ions Eu3+ in MgAl2O4 nanocrystals depends on the calcination temperature. When europium is introduced into the aluminium magnesium spinel, the crystalline structure is disordered. It was found that unlike calcination temperature, duration of heat treatment does not affect powders properties. It was shown that strong structural and luminescence changes take place when calcination temperature is near 2/3 of MgAl2O4 melting temperature. The optimal conditions for synthesis nanopowders were determined as follows: Т1=600°Сt1=1.5h, Т2=850°Сt2=2h.

Rietveld refinement, micro-structural, optical and thermal parameters of zirconium titanate composites

Pure titania and zirconium titanate composites have been synthesized using sol-gel technique and annealed at 650, 875 and 1100°C for 4h. Acetylacetone was used to control the rate of hydrolysis of precursors. The Rietveld refinement, micro-structural, optical and thermal parameters of prepared composites was investigated. Effect of annealing and concentration of Zr and Ti in composites on their crystal structure, morphology, PL emission wavelength and band gap have been studied. X-ray diffraction and Rietveld analysis exhibit that all prepared samples of composites have orthorhombic single phase of zirconium titanate with space group pbcn. The lower values of profile parameters such as Rp, Rwp, RB, RF, χ2 indicated that the calculated diffraction pattern is in fair agreement with observed pattern. The increase in zirconia concentration decreases the degree of crystallization of ZrTiO4. The photoluminescence spectra show the blue shifting of emission peak at 420nm as the zirconia concentration increases. The optical band gap of zirconium titanate composites also blue shifted (3.24–3.64eV) with decrease in crystallite size of composites.

Electric modulus, scaling and ac conductivity of La2CuMnO6 double perovskite

A sample of La2CuMnO6 (LCM) was synthesized through the standard solid state reaction method. X-ray diffraction experiments and Rietveld analysis reveal that the material crystallizes in an orthorhombic structure. SEM image displayed well-defined regular shaped nearly spherical and unequal grains with grain-size lies between 2.5 and 3.0 μm ranges. Frequency dependence of dielectric, electric modulus and ac conductivity of LCM has been studied as a function of both frequency and temperatures. The conduction mechanism is explained using universal power law (σ (ω, T) = B ωn(T)). The Kohlrausch–Williams–Watts (KWW) model approaches were employed to fit frequency response curves of M′ and M″. The large asymmetry of M″(f) peaks were explained by stretched exponent parameter (β). Activation energy values suggest that the conduction mechanism and relaxation process have a different origin. The ε′ and ε″, as a function of normalized frequency, exhibit better master curves than M″ vs M′ data.

Effects of Cu doping on the electronic structure and magnetic properties of MnCo2O4 nanostructures

Reported here are the results and their analysis from our detailed investigations of the effects of Cu doping () on the electronic structure and magnetic properties of the spinel O4. A detailed comparison is given for the and cases for both the bulk-like samples and nanoparticles. The electronic structure determined from x-ray photoelectron spectroscopy and Rietveld analysis of x-ray diffraction patterns shows the structure to be: ()A]B i.e. substitutes for on the octahedral B-sites. For the bulk samples, the ferrimagnetic K for is lowered to K for the sample, this decrease being due to the effect of Cu doping. For the nanosize () sample, the lower K ( K) is observed using analysis, this lowering being due to finite size effects. For , fits of dc paramagnetic susceptibility data of versus T in nanosize samples to the Néel expression are used to determine the exchange interactions between the A and B sites with exchange constants: K (4.1 K), K (16.3 K) and K (13.8 K) for . The temperature dependence of ac susceptibilities and at different frequencies shows that in bulk samples of and , the transition at TC is the normal second order transition. But for the nanosize and 0.2 samples, analysis of the ac susceptibilities shows that the ferrimagnetic transition at TC is followed by a re-entrant spin-glass transition at lower temperatures K (138 K) for (). Analysis of the ac susceptibilities, and , versus T data is done in terms of two scaling laws: (i) Vogel–Fulcher law ; and (ii) power law of critical slowing-down . These fits confirm the existence of glassy behavior below TSG with the parameters (8.91), (9.6 × 10) and K (∼138 K) for the samples (0.2), with similar results obtained for other samples. The linear behavior of the peak maximum in versus (AT-line) further supports the existence of glassy states in nanosize samples. For , the temperature and composition dependence of the hysteresis loop parameters are investigated; all the samples with x ⩾ 0.1 have the coercivity HC and remanence . Since the results reported here in these nanostructures are significantly different from those in bulk , further investigations of their magnetic structures using neutron diffraction are warranted.

Synthesis and Structural Characterization of a CHA-type AlPO4 Molecular Sieve with Penta-Coordinated Framework Aluminum Atoms.

The structure-directing effects of a series of polymethylimidazolium cations with different numbers of methyl groups as organic structure-directing agents (OSDAs) in the synthesis of aluminophosphate (AlPO4)-based molecular sieves in both fluoride and hydroxide media are investigated. On the one hand, among the OSDAs studied here, the smallest 1,3-dimethylimidazolium and the largest 1,2,3,4,5-pentamethylimidazolium cations were found to direct the synthesis of a new variant of the triclinic chabazite (CHA)-type AlPO4 material, designated AlPO4-34(t)V, and the one-dimensional small-pore silicoaluminophosphate (SAPO) molecular sieve STA-6 in hydroxide media, respectively. On the other hand, the intermediate-sized 1,2,3,4-tetramethylimidazolium cation gave SSZ-51, a two-dimensional large-pore SAPO material, in fluoride media. Synchrotron powder X-ray diffraction and Rietveld analyses reveal that as-made AlPO4-34(t)V contains penta-coordinated framework Al species connected by hydroxyl groups, as well as tetrahedral framework Al, which contrasts with the distortions arising from the two F- or OH- bridges between octahedral Al atoms in all already known AlPO4-34 materials. The presence of Al-OH-Al linkages in this triclinic AlPO4-34 molecular sieve has been further corroborated by thermal analysis, variable-temperature IR,27Al magic-angle spinning NMR, and dispersion-corrected density functional theory calculations.

Effect of Testing Factors on Rietveld Quantitative Analysis of Cement-Matrix Materials

For cement-matrix materials, the microstructure plays a vital important role in the research. Recently, quantitative phase analysis of cementitious materials can be performed using the Rietveld method by fitting the calculated X-ray diffraction (XRD) profile with the observed one. The aim of this paper is to further perform the quantitative analysis by the Rietveld method and discuss the influence of testing factors on the Rietveld quantitative phase analysis. The factors included the collection range of pattern, step size and the scan time of per step. In this study, the chemical composition of the samples was determined by X-ray fluorescence (XRF) spectrometry. And their phase composition was calculated by X-ray powder diffraction and Rietveld analysis. The results showed that the collection range of pattern depended on the tested materials , and the scanning range should include the main diffraction peak of the sample. Smaller step size and longer scan time of each step made the fitting factor smaller, also the calculated pattern coincided with the measured pattern, better enhance the precision of the analyses.

On the peculiarities of phase developments involving Zn2 +-doped ZrO2 system

ZnO-stabilized (8%) ZrO2 system appeared cubic in normal X-ray diffraction (at 500°C) but Rietveld analyses confirmed equiproportionate (~1:1) cubic and tetragonal phase. At 650°C, the cubic to tetragonal phase ratio changed to 1:2 with the appearance of monoclinic phase (8wt%). Kinetic studies with thermogravimetry data and other structural characterizations established the importance of the stabilizing cation (Zn2+) for the ZrO2 matrix and confirmed that the conversion of the stabilized cubic/tetragonal phase to monoclinic ZrO2 is dependent pivotally on process kinetics (rate of heat supply), thermodynamics (absolute final temperature) and the presence/lack of oxygen in the ambience.

Al and PEG Effect on Structural and Physicochemical Properties of CoFe2O4

In this work, pure and Alumina doped cobalt ferrite nanoparticles CoFe2−xAlxO4 (for x = 0.44) have been synthesized by the sol gel method. The influence of alumina doping on the morphological and mechanical properties of CoFe2O4 nano-particles were investigated by means of X-ray powder diffraction (XRD) and rietveld analysis. XRD analysis confirmed that the single phase formation of pure nano particles with the expected cubic inverse spinel structure with Fd3m space group and without any impurity phase. Alumina doping were led to a decrease in the crystallite size, lattice parameter, elastic constants and magnitude of moduli. It is explained on the basis of the replacement of Fe ions with half-filled d-shell (3d5) and larger radius by Al3+ ions with a completely filled shell (2p6) and smaller radius.

Evolution of magnetic and transport properties in hole doped Y2Ir2O7

We report the effect of Ru4+ substitution at Ir-site on structural, magnetic and electrical properties in pyrochlore iridate Y2Ir2O7. Structural investigation has been done using x-ray powder diffraction and Rietveld analysis for both samples. There is no structural phase transition with Ru doping. Magnetization study shows that on slightly substitution of Ru at Ir-site effectively shifts the magnetic irreversible temperature Tirr towards low temperature and reduce the bifurcation between MZFC and MFC branches. The electrical resistivity shows an insulating behavior in whole temperature range, however, resistivity decreases with doping of Ru.

Magnetic interactions in rhenium-containing rare earth double perovskites Sr2LnReO6 (Ln=rare earths)

The perovskite-type compounds containing both rare earth and rhenium Sr2LnReO6 (Ln=Y, Tb-Lu) have been prepared. Powder X-ray diffraction measurements and Rietveld analysis show that Ln3+ and Re5+ ions are structurally ordered at the B site of the perovskite SrBO3. Magnetic anomalies are found in their magnetic susceptibility and specific heat measurements at 2.6–20K for Ln=Y, Tb, Dy, Yb, Lu compounds. They are due to magnetic interactions between Re5+ ions. The results of the magnetic hysteresis and remnant magnetization measurements for Sr2YReO6 and Sr2LuReO6 indicate that the antiferromagnetic interactions between Re5+ ions below transition temperatures have a weak ferromagnetic component. The analysis of the magnetic specific heat data for Sr2YbReO6 shows that both the Yb3+ and Re5+ ions magnetically order at 20K. For the case of Sr2DyReO6, magnetic ordering of the Re5+ moments occurs at 93K, and with decreasing temperature, the moments of Dy3+ ferromagnetically order at 5K from the measurements of magnetic susceptibility and specific heat.

Curie temperature enhancement with reserving a reasonable magnetoresistance by Pr substitution in Ba2FeMoO6

In the present work samples of Ba2−xPrxFeMoO6 double perovskites with x=0 – 0.75 were synthesized at high temperature of 1523K in the flowing of Ar+H2 forming gas with H2 concentration of 5%. The results of X-ray powder diffraction and Rietveld analysis indicate that the crystal structure of Ba2−xPrxFeMoO6 is cubic with space group of Fm3̅m. The Pr doping has reduced the lattice parameter and bond lengths of Pr/Ba-O and Fe/Mo-O which, have been estimated by Rietveld analysis (FULLPROF), consequently it enhances the ferrimagnetic transition temperature (TC). On the other hand, it increases gradually the probability of antisite disorder which is the main reason for the decrease of the magnetization. Also, it produces more conducting channels in the samples causing enhancement of conductivity at low doping ratio for x≤0.3 but the effect is reversed at higher doping ratio for x>0.3. The behavior of magnetoresistance (MR), with temperature shows intergrain magnetoresistance at low temperature which depends on the extrinsic properties, and intragrain magnetoresistance at room temperature which depends on intrinsic properties. Finally, it is worth mentioning that in the samples of x=0.1, 0.2 and 0.75 a considerable Curie temperature enhancement has occurred with reserving a reasonable magnetoresistance which may be promising in different applications.

Relaxation Analysis of Electrochemically Lithium Inserted γ-Fe2O3 By Using a Solid-State Li NMR

Introduction Recently, we have conducted the relaxation analysis for various electrode materials such as γ-Fe2O3 [1-2], LiMn2O4 [3], LiFePO4 [4], LiCoO2 [5], and graphite [6] after termination of electrochemical Li insertion/extraction. The relaxation analysis makes transition of electrode material from kinetic state to equilibrium state clear [7]. For γ-Fe2O3 with spinel structure, we have reported that the iron occupancy of 8a site decreased and that of 16c site increased with lithium insertion process and the iron occupancy of 8a site increased and that of 16c site decreased gradually at the relaxation process after termination of lithium insertion by using the X-ray Rietveld analysis. We considered that this indicates that lithium prefer 8a site to occupy kinetically, on the other hand, prefer 16c site thermodynamically. In this study, we investigated the lithium behavior directly by using a solid-state Li nuclear magnetic resonance (NMR) of electrochemically lithium inserted γ-Fe2O3 at the relaxation process. Experiment Electrochemical lithium insertion into γ-Fe2O3 has been made by using an Ar-sealed glass beaker cell. The mixture of γ-Fe2O3 powder (Alfa Aesar, >99%), Acetylene Black (AB) and PTFE powder with the weight ratio of 70:30:5 was employed for cathode material, which was spread onto a Ni mesh as a current collector. Lithium foil was used as the reference and counter electrodes, and 1 M LiPF6 in EC/DMC (2:1 v/v%, Kishida Chemical Co., Ltd) was used as the electrolyte. Lithium ion has been electrochemically inserted into the sample at a constant current of 0.01 Ag-1 to obtain Li1.5Fe2O3. After the termination of lithium insertion, the sample was scraped immediately out of the Ni mesh and set into a quartz tube. We prepared three samples for analysis of relaxation behavior. The relaxation time after the termination of lithium insertion of each sample were 15 h, 38 h and 2967 h, respectively. 7Li NMR spectra of the samples were acquired at room temperature in an AVANCE400 (Bruker Biospin) instrument at a spinning frequency of 0 kHz and using the Hahn echo sequence, taking 1 M aqueous solution of LiCl, at 155.65 MHz of resonance frequency as reference. Results and discussion Figure 1 shows the measured NMR spectra (Hahn echo, static) of the three samples. We separated the spectrum into two waveforms. We named the waveform at lower chemical shift as W1 and that at higher chemical shift as W2. For either sample, the total waveform of W1 and W2 is well fitted to the measured waveform as shown in Fig. 1. It is considered that W1 and W2 represents the two different conditions of lithium in the samples. The peak intensity ratios of W1 to W2 for samples with the relaxation time of 15 h, 38 h, and 2967 h were 1.05, 1.21 and 1.56, respectively, which increased with the increase of the relaxation time. According to the relaxation analysis by using the X-ray Rietveld method [1], it is considered that lithium at 8a site increases and at 16c site decreases with the increase of the relaxation time. If we ascribe W1 to lithium at 16c and W2 to that at 8a, the change in the intensity ratio is very consistent with the above consideration from the X-ray Rietveld analysis. In conclusion, we succeeded to observe lithium relaxation behavior directly by the NMR spectra, which coincided with that presented by the X-ray Rietveld analysis.

Physical salt attack on concrete incorporating nano-silica

The damage induced by crystallization of salts (physical salt attack, PSA) has been often misidentified as chemical attack. Under certain environmental conditions, PSA may cause notable surface damage of concrete partially embedded in salt-rich soils. The process is similar to salt weathering of natural rocks. The current study investigated the effect of refining the microstructure of concrete by nano-silica additions on its resistance to PSA in an accelerated procedure. Specimens were partially immersed in a high-concentration sodium sulphate solution and simultaneously exposed to cyclic temperature and relative humidity. Specimens’ deterioration was monitored for more than 100 cycles of exposure. Also, an effort was made to analyse the relationships between specimen damage, characteristics of pore structure and absorption capacity. Finally, the immersed and drying portions of specimens were tested by X-ray diffraction and Rietveld analysis and scanning electron microscopy to identify the root cause of damage.

Synthesis and Characterization of Fe<sub>3</sub>O<sub>4</sub> Nanoparticles Stabilized by Polyvinylpyrrolidone/Polyethylene Glycol with Variable Mass Ratios

Magnetic nanoparticles are devices able to optimize cancer treatments. In particular, magnetite nanoparticles are very effective in producing heat to cause lysis of tumor cells. However, in order that nanoparticles are internalized without causing damage to body they must be coated by biocompatible material. In this work, Fe3O4 nanoparticles were coated by a polymer blend: polyethylene glycol / polyvinylpyrrolidone. Some variations in mass ratio of polymer mixture were made. The effect of varying mass ratio in polymers was investigated. Samples were characterized by X-ray diffraction and Rietveld analysis. Moreover, hysteresis curves were analyzed. The results indicate good agreement between mass proportions used and physical and magnetic properties of nanocomposite.

Direct Observation of Luminescent Silver Clusters Confined in Faujasite Zeolites.

One of the ultimate goals in the study of metal clusters is the correlation between the atomic-scale organization and their physicochemical properties. However, direct observation of the atomic organization of such minuscule metal clusters is heavily hindered by radiation damage imposed by the different characterization techniques. We present direct evidence of the structural arrangement, at an atomic level, of luminescent silver species stabilized in faujasite (FAU) zeolites using aberration-corrected scanning transmission electron microscopy. Two different silver clusters were identified in Ag-FAU zeolites, a trinuclear silver species associated with green emission and a tetranuclear silver species related to yellow emission. By combining direct imaging with complementary information obtained from X-ray powder diffraction and Rietveld analysis, we were able to elucidate the main differences at an atomic scale between luminescent (heat-treated) and nonluminescent (cation-exchanged) Ag-FAU zeolites. It is expected that such insights will trigger the directed synthesis of functional metal nanocluster-zeolite composites with tailored luminescent properties.

High-Pressure Synthesis of Manganese Oxyhydride with Partial Anion Order.

The high-pressure synthesis of a manganese oxyhydride LaSrMnO3.3 H0.7 is reported. Neutron and X-ray Rietveld analyses showed that this compound adopts the K2 NiF4 structure with hydride ions positioned exclusively at the equatorial site. This result makes a striking contrast to topochemical reductions of LaSrMnO4 that result in only oxygen-deficient phases down to LaSrMnO3.5 . This suggests that high H2 pressure plays a key role in stabilizing the oxyhydride phase, offering an opportunity to synthesize other transition-metal oxyhydrides. Magnetic susceptibility revealed a spin-glass transition at 24 K that is due to competing ferromagnetic (Mn(2+) -Mn(3+) ) and antiferromagnetic (Mn(2+) -Mn(2) , Mn(3+) -Mn(3+) ) interactions.

Structural and magnetic properties of LaCrO3 half-doped with Al

Structural and magnetic properties of LaCrO3 half-doped with Al are reported in this work. Pure and half-doped samples were prepared by combustion synthesis using urea as fuel. The crystal structure was investigated by X-ray diffraction and Rietveld analysis. A structural phase transition caused by a decrease of the chemical pressure was observed. The scanning electron microscopy (SEM) images show the formation of porous samples with particles of irregular morphologies. A quantitative Energy-dispersive X-ray spectroscopy (EDS) analysis on the surface indicates the inclusion of the Al on the structure. However, a small deficiency of La and Al was observed. Magnetization measurements as a function of temperature reveal an antiferromagnetic order in both samples. A large decrease of TN (Néel temperature) and a reduction of the frustration factor is observed in the sample doped with Al. The magnetic isothermal at 5K shows a typical antiferromagnetic behavior with a slightly spin canting for the doped sample.