Local Structural Disorder Research Articles

Pressure-induced structural transformations in In2-x Yx (MoO4 )3 systems

In this work, we report results of high-pressure Raman experiments (P < 8 GPa) on In2-xYxMo3O12 for x = 0.0 and 0.5. A crystalline to crystalline structural phase transition and pressure-induced amorphization (PIA) have been identified. The structural phase transition takes place at 1.5 and 1.0 GPa for In2(MoO4)3 and In1.5Y0.5(MoO4)3, respectively, resulting in the change of structure from monoclinic P21/a to a more denser structure. The PIA started at 5 and 3.4 GPa for In2Mo3O12 and In1.5Y0.5Mo3O12, respectively. The amorphization process takes place in two stages in the case of In1.5Y0.5Mo3O12 phase, while for In2Mo3O12, it is not complete until the pressure is as high as 7 GPa. Our results also suggest that with increase of ionic size of the A3+ ions, the octahedral distortion increases and consequently larger local structural disorder is introduced in the A2(MoO4)3 system, where A is a trivalent ion (In, Y3+, Sc3+, Fe3+, etc.). Copyright © 2015 John Wiley & Sons, Ltd.

Influence of local structural disorders on spectroscopic properties of multi-component CaF2–Bi2O3–P2O5–B2O3 glass ceramics with Cr2O3 as nucleating agent

Multi-component CaF2–Bi2O3–P2O5–B2O3 glasses doped with different concentrations of Cr2O3 were crystallized through heat treatment. The prepared glass ceramic samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and differential thermal analysis (DTA). Spectroscopic studies viz., optical absorption, Fourier transform infrared (FTIR), Raman and electron paramagnetic resonance (EPR) were carried out. The XRD, SEM and DTA studies indicated that the samples contain different crystalline phases. Results of optical absorption and EPR studies pointed out the gradual conversion of chromium ions from Cr3+ state to Cr6+ state with an increase of Cr2O3 content from 0.1 to 0.5mol%. The results of FTIR, Raman and EPR studies revealed that Cr6+ ions participate in the glass network in tetrahedral positions and seemed to increase the polymerization of the glass ceramics. The quantitative analysis of results of the spectroscopic studies further indicated that the glasses crystallized with low concentration of Cr2O3 are favourable for solid state laser devices.

Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

We report for the first time a rapid preparation of Zn1−2xCoxNixO nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green–orange–red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO.

Origin and significance of the yellow cathodoluminescence (CL) of quartz

The origin of yellow cathodoluminescence (CL) in quartz has been investigated by a combination of CL microscopy and spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and spatially resolved trace-element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The study shows that the appearance of a ~570 nm (2.17 eV) emission band can be attributed to high oxygen deficiency and local structural disorder in quartz. A proposed luminescence center model implies self-trapped exciton (STE) emission from localized amorphized regions in quartz. Although the high-intensity emission at 570 nm is in general consistent with high concentrations of E ′1 defects detected by EPR spectroscopy, CL studies with different electron beam parameters and annealing experiments up to 600 °C show a temperature and irradiation dependence of the luminescence related defects excluding the role of E ′1 centers as direct luminescence activators for the 570 nm emission. The evaluation of geochemical data shows that quartz with yellow CL occurs in low-temperature hydrothermal environment (mostly <250 °C) and is related to fast crystallization in an environment with oxygen deficiency.

Impedance spectroscopic studies of mixed alkali tellurite glasses

The mixed alkali tellurite glasses for the glass system 0.70TeO2·(0.30 − x)Na2O·xK2O (x = 0.0 and 0.05) were prepared by conventional melt-quench method. The investigated glasses are characterized by impedance spectroscopic technique. The impedance behavior included the contribution of bulk or glassy matrix was found at lower temperatures and a few electrode contributions at higher temperatures. Scaling analysis of the complex modulus showed excellent temperature superposition indicated that the ion transport mechanism remains the same throughout the measured range of temperatures. Some deviations from scaling at higher frequencies are observed due to local structural disorder caused by structural transition in the tellurite glass network.

Band gap tailoring and enhanced ferromagnetism in Yb doped SrWo4 scheelite structured system

Room temperature ferromagnetism and enhanced optical property of Yb doped SrWO4 compounds have been investigated for the importance in the field of spintronics. Pristine and Yb doped SrWO4 compounds were synthesized by simple chemical precipitation method. Powder X-ray diffraction analysis reveals the scheelite type tetragonal structure of all the prepared compounds. The crystallite size and lattice strain was calculated by Williamson–Hall plot. The local structural disorder of the compounds was investigated by Laser Raman spectroscopy and it was found that the local disorder induced by the dopant leads to alteration in Raman active modes of Yb doped SrWO4 compounds. The formation of microsphere and platelets like shapes of particulate system was examined by electron microscopy techniques. The evidences for oxygen vacancy and oxidation states of elements present in the compounds were analyzed by X-ray photoemission spectroscopy. In UV–Vis spectra, distinctive shift of absorption edge was observed exclusively for all the Yb doped SrWO4 compounds. The presence of defective states with prominent blue and green emission of the compounds was investigated by photoluminescence spectroscopy. Magnetization study reveals that the pristine SrWO4 compound exhibits unsaturated ferromagnetic behaviour, whereas all the Yb doped SrWO4 compounds demonstrates saturated ferromagnetic behaviour. The enhancement of magnetization and ferromagnetic ordering of the compounds has been explained in terms of carrier-induced Ruderman–Kittel–Kasuya–Yosida interaction theory. Hence, from the present investigation it was observed that the doping of Yb in SrWO4 will yields a new kind of multifunctional material for fabricating magneto-optical and electronic devices.

Enhanced ferromagnetism and emergence of spin-glass-like transition in pyrochlore compound Dy2Ti2−xVxO7

We have studied the magnetic properties of spin-frustrated compound Dy2Ti2−xVxO7 single crystals. Bulk magnetization data show that ferromagnetic interaction enhances with increasing content of V, resulting from the ferromagnetic interactions between Dy and V ions. It is also found from ac susceptibility that the modestly doped samples (x≤0.4) still keep ice state, demonstrating the robustness of spin ice. When the doped concentration increases up to 0.5, more disorder on B site and internal field associated with V4+ ions would affect the macroscopic ground-state degeneracy and relieve the frustration, leading to the disappearance of spin ice and occurrence of a spin-glass-like transition. The magnetic properties of the system are related to magnetic frustration and local structural disorder.

Organic Solar Cells and its Characteristics

This paper describes the characteristics of organic solar cell. Several characteristics impact on the conversion efficiency of organic solar cells was discussed. Recently, organic solar cells are attracting a lot of attention due to flexibility, low cost, light weight and large-area applications, and significant improvement in the power conversion efficiency. But the efficiencies of organic solar cells are still lower than crystal silicon solar cells. A circuit model of the solar cell provides a quantitative estimate for losses in the solar cell to interpret the characteristics of the solar cell. However, compared with inorganic solar cells, organic solar cells are lack of a three-dimensional crystal lattice, different intramolecular and intermolecular interactions, local structural disorders, amorphous and crystalline regions, and chemical impurities. Therefore, an appropriate model is represented in the paper.

Electrical mobility of silver ion in Ag2O-B2O3-P2O5-TeO2 glasses.

The effect of adding TeO(2) into (100 - x)[0.5Ag(2)O - 0.1B(2)O(3) - 0.4P(2)O(5)] - xTeO(2), with 0-80 mol % TeO(2) glass, on the structural changes and electrical properties has been investigated. DSC and thermodilatomery were used to study their thermal behavior, structure was studied by Raman spectroscopy, and electrical properties have been studied by impedance spectroscopy over a wide temperature and frequency range. The introduction of TeO(2) as a third glass former to the glass network causes the structural transformation from TeO(3) (tp) to TeO(4) (tbp) which contributes to the changes in conductivity. The glasses with low TeO(2) content show only a slow decrease in dc conductivity with addition of TeO(2) due to the increase of the number of nonbridging oxygens, which increases the mobility of Ag(+) ions. The steep decrease in conductivity for glasses containing more than 40 mol % TeO(2) is a result of decrease of the Ag(2)O content and stronger cross-linkage in glass network through the formation of more Te-(eq)O(ax)-Te bonds in TeO(4) tbp units. The glasses obey ac conductivity scaling with respect to temperature, implying that the dynamic process is not temperature dependent. On the other hand, the scaling of the spectra for different glass compositions showed the deviations from the Summerfield scaling because of the local structural disorder which occurs as a result of the structural modifications in the tellurite glass network.

Conformational Changes and Phase Behaviour in the Protic Ionic Liquid 1‐Ethylimidazolium Bis(trifluoromethylsulfonyl)imide in the Bulk and Nano‐Confined State

AbstractWe report a Raman spectroscopic study of conformational changes to the TFSI anion in the protic ionic liquid 1‐ethylimidazolium bis(trifluoromethylsulfonyl)imide, [C2HIm][TFSI], in its bulk and nano‐confined state. We show that the TFSI anion is found as a mixture of cis and trans conformations at room temperature and in the liquid state, whereas this equilibrium shifts towards an increased cis population upon confinement in silica. In addition, the strong Raman signature at ca. 743 cm–1 assigned to TFSI is found at systematically higher frequencies in the confined state. These findings suggest a higher packing efficiency, or density, for the ionic liquid at the silica surface. Moreover, the enthalpy of conformational change is only marginally affected upon confinement (4.32 ± 1.30 vs. 5.27 ± 1.09 kJ mol–1), and the entropy is found to be a few J mol–1 K–1 higher in the confined state. Raman spectra recorded upon heating from very low temperatures show that the phase behaviour of the ionic liquid is also affected by confinement, with crystallization upon cooling being frustrated in favour of an amorphous glassy phase. To summarize, our results indicate that the interaction established in the ionogels between the silica surface and the protic ionic liquid [C2HIm][TFSI] favours local structural disorder, in conceptual agreement with the slightly higher experimentally estimated entropy.

The erbium׳s amphoteric behavior effects on sodium bismuth titanate properties

The effects of erbium doping on lead-free ferroelectric Na0.5Bi0.5TiO3 ceramics are investigated. The scanning electron microscopy shows a highly dense grain structure for all specimens. A pure perovskite structure was observed by X-ray diffraction for all compositions. However, Raman spectroscopy investigations suggest that Er3+ doping is associated with local structural disorder. Doping with Er3+ ions also leads to photoluminescence effect. The depolarization temperature in the dielectric measurement vanishes gradually as the Er3+ amount increases. The ferroelectric properties display a slight decrease in coercive field for the x=0.01 composition.

Study on dual-source and image reconstruction technique application in lumbar spondyloschisis without sliding

Objective To explore the technical advantages and clinical value of dual-source and image reconstruction technique application in lumbar spondyloschisis without sliding. Methods 36 cases of patients with LSWS were collected who were examined by dual-source CT scan and diagnosed definitely. 18 cases of patients were examined by X-ray （ including lumbar vertebrae and double oblique）. The diagnosis rate of X-ray and CT scanning in diagnosing LSWS were calculated, which was made statistical analysis. The image of 36 cases patients with LSWS were reconstructed by multi-planar reconstruction（MPR） ,volume rendering technique（VR）and curved planar reconstruction（CPR）. The display rate was calculated, which was made statistical analysis according to various image reconstruction in diagnosing I_SWS. Results 7 cases of patients with LSWS were found by X-ray examination. 36 cases of patients with LSWS were found by dual-source CT examination. The display rate was 38.9% and 100.0%. 71 LSWS were found in 36 cases of patients with LSWS ,35 cases were bilateral spondylolysis, 1 case was unilateral spondylolysis. In several image reconstruction methods, CPR and cutting VR showed the highest rate in diagnosing LSWS, which was 100.0%. The symptom of LSWS in X-ray examination：local thinning and structural disorder in lumbar spondylol- ysis, cortical discontinuity. The symptom of LSWS in CT examination were as follows ： clear linear low density shadow in lumbar,ends hardening and bone fragments in some case. Conclusion The dual-source CT and its image recon- struction technology have the technological superiority and higher clinical value in diagnosing LSWS,which is crucial to prevent LSWS misdiagnosed, and could become the preferred examination in screening and diagnosing LSWS. Key words: Lumbar Spondylolysis Without Sliding; Dual-source CT; Image Processing, Computer - Assisted

Local Structure and Superconducting Properties of Bi 2 Te 3 -Doped YBa 2 Cu 3 O 7 − δ

The samples of (Bi2Te3) x (YBa2Cu3 O 7−δ) 1−x (x = 0, 2.5 %) have been synthesized at normal pressure, and the effect of the doping of topological insulator Bi2Te3 on the superconductor YBa2Cu3 O 7−δ is studied. The diamagnetism properties are investigated by zero-field cooling DC magnetization measurement. In the Bi2Te3-doped sample, an enhancement of superconducting fractions is observed, and the superconducting transition temperature (T c ) increases. For the sample with x= 2.5 %, the phase transition of the tetragonal phase to the orthorhombic phase is observed by X-ray diffraction, and the increase of the degree of local structure disorder is confirmed by extended X-ray absorption fine structure, so it can be concluded that the superconducting fraction enhancement is attributed to the phase transition induced by the addition of topological insulator Bi2Te3. Scanning electron microscopy images show that the added Bi2Te3 is found to adhere to the surface of YBa2Cu3 O 7−δ grains, and it is considered that the strain induced by grains’ interaction leads to the phase transition which enhances the degree of local structure disorder at the same time. An absorption edge shift to the high-energy side is observed by the X-ray absorption near-edge structure. The edge shift can be attributed to the electron transfers from YBa2Cu3 O 7−δ to the additives. It is widely accepted that the hole intensity is closely related with T c , so in YBa2Cu3 O 7−δ the added holes by the transition may lead to the enhancement of T c . Thus, it can be concluded that the topological insulators can produce structural and electronic effect on the YBCO superconductors in the composite materials.

A Modular Concept of Crystal Structure Applied to the Thermal Transformation of α‐C2SH

A single crystal of α‐Ca2[HSiO4](OH) (α‐C2SH) was repeatedly imaged at room temperature with synchrotron mid‐infrared microscopy after heating to 310°C, 340°C, 370°C, and 400°C respectively. The mechanisms of the observed phase transformations are discussed on the basis of a modular concept of the crystal structures. All images show domains of dellaite, Ca6[Si2O7][SiO4](OH)2, which are predominantly formed in the core of the crystal. In the crystal rim area α‐C2SH persists in higher abundance. The mechanism of the phase transformation of α‐C2SH into dellaite includes the following: (1) Partial formation of killalaite (Ca3[HSi2O7](OH)) as nuclei according to the isochemical reaction 2Ca2[HSiO4](OH) → Ca3[HSi2O7](OH) + Ca(OH)2 probably induced by anisotropic thermal expansion, local chemical fluctuations, structural (proton) disorder, and different bond strengths of the OH groups in the α‐C2SH structure. (2) Further dehydration of killalaite and α‐C2SH domains results in the formation of dellaite according to Ca3[HSi2O7](OH) + Ca(OH)2 + Ca2[HSiO4](OH) – 2H2O → Ca6[Si2O7][SiO4](OH)2. The results suggest that the polymerization of two isolated [HSiO4] tetrahedra takes place without dehydration according to reaction (1) rather than through condensation with simultaneous H2O release: 2[HSiO4] → [Si2O7] + H2O. We suggest that reaction (1) cannot be completed at ambient pressure. Thus in the regions close to the rim of the crystals we expect the formation of x‐C2S, which starts along the crystal edges according to Ca2[HSiO4](OH) → Ca2SiO4 + H2O. Based on a modular concept, a structural relationship between α‐C2SH, killalaite, dellaite, and x‐C2S has been established. Similarities and differences in the thermal behavior of α‐C2SH and afwillite have been highlighted.

The composite ceramics of (YBa2Cu3O7−δ)1−x(Fe3O4)x

The effect of sintering temperatures on the superconducting properties of the composites of (YBCO)0.975(Fe3O4)0.025 (2.5wt.%) has been studied. The field-cooled measurement finds that with the sintering temperature increasing the superconducting fraction is increased first and then decreased. The optimum sintering temperature is found. The Raman vibration modes (out-of-phase bond-buckling mode and in-plane bond-stretching mode) are recorded at room temperature. The extended X-ray absorption fine structure proves that no further lattice distortion occurs on YBCO after the addition of Fe3O4, but the local structure disorder of YBCO has altered as the sintering temperatures changed. Compared the shift of the Raman phonon modes with the magnitude of oscillations of extended X-ray absorption fine structure in R space it can be concluded that the local disorder has relation with superconducting properties. Scanning electron microscopy images show that the doped Fe3O4 are diffused into the inter-grain sites. With sintering temperature increasing the small-size grains get fused to form larger grains. The strain produced by grain interaction leads to the change of local structure disorder. Whereas, further increase of the sintering temperatures, some Fe ions at the grain boundaries are incorporated into the unit cell of YBCO, which leads to the decrease of superconducting fractions. By X-ray absorption near edge structure, it is found that the white lines occurring near K edge of Cu2+ show an energy shift toward high energy side. It can be considered that as the sintering temperature increases more holes are formed and the screening effect around the Cu2+ weakens. The screening behavior is also conducive to the formation of superconducting fractions.

Assessment of local structural disorders of the bladder wall in partial bladder outlet obstruction using polarized light imaging

Partial bladder outlet obstruction causes prominent morphological changes in the bladder wall, which leads to bladder dysfunction. In this paper, we demonstrate that polarized light imaging can be used to identify the location of obstruction induced structural changes that other imaging modalities fail to detect. We induced 2-week and 6-week partial outlet obstruction in rats, harvested obstructed bladders, then measured their retardances while distended to high pressures and compared them to controls. Our results show that the retardance of the central part of the ventral side (above the ureters) closer to the urethra can be used as a potential metric of the distending bladder obstruction.

Atomic distribution, local structure and cation size effect in o-R1−xCaxMnO3 (R = Dy, Y, and Ho)

We propose new interatomic potentials for the small rare-earth-based orthorhombic RMnO3 (R = Dy, Y, Ho), which accurately model the structural properties of these extreme cases of lanthanide manganate series. They are further employed to investigate the intrinsic defects in o-RMnO3 and the cation distribution and local structure in o-R1−xCaxMnO3 (R = Dy, Y, Ho). Schottky disorders are found to be the dominant structural defects, and the possibility of a small degree of anti-site disorder of R and Mn ions over A and B sites is found. The introduced Ca dopants tend to form chemically and structurally like CaMnO3 clusters in the lightly doped system, which can be regarded as representations of microscopic phase separation. The local structural disorder is reduced with increasing doping density. For o-R0.5Ca0.5MnO3 (R = Dy, Y, Ho), the charge ordering state is intrinsically favored, and the layer stripe model is shown to be energetically more favorable and structurally more reasonable. Moreover, the tendency to form charge ordered stripes increases with the decrease of R size. The local structure in the layer stripe pattern deviates largely from the average structure: RMnO3-like and CaMnO3-like layers are formed. The size of R ion has a significant influence on the doping effect on Jahn–Teller (JT) distortion and a manganate with a larger R will experience a larger reduction on the anisotropy of Mn–O bonds in Mn3+O6 octahedra. However, the change of octahedral tilting upon doping does not vary much with R radii.

Phonon Scattering through a Local Anisotropic Structural Disorder in the Thermoelectric Solid Solution Cu2Zn1–xFexGeSe4

Inspired by the promising thermoelectric properties of chalcopyrite-like quaternary chalcogenides, here we describe the synthesis and characterization of the solid solution Cu(2)Zn(1-x)Fe(x)GeSe(4). Upon substitution of Zn with the isoelectronic Fe, no charge carriers are introduced in these intrinsic semiconductors. However, a change in lattice parameters, expressed in an elongation of the c/a lattice parameter ratio with minimal change in unit cell volume, reveals the existence of a three-stage cation restructuring process of Cu, Zn, and Fe. The resulting local anisotropic structural disorder leads to phonon scattering not normally observed, resulting in an effective approach to reduce the lattice thermal conductivity in this class of materials.

Local structural disorder in Zn0.9Co0.1O nanocrystals studied using neutron total scattering analysis

Neutron total scattering measurements were performed at 300 K and 15 K to study local structural disorder in deuterium plasma treated and as-prepared Zn0.9Co0.1O nanocrystalline powder. We found that static disorder becomes a determining factor for atomic pair correlations on the length scale larger than r∼9Å. On the source of the static disorder, we propose a partial occupancy of Zn/Co further away from its crystallographic site along the c-axis. Between the deuterium plasma treated and as-prepared Zn0.9Co0.1O samples, we observed no local structural difference, which suggests that no additional disorder is induced by the deuterium plasma treatment.

Local Ordering Changes in Pt–Co Nanocatalyst Induced by Fuel Cell Working Conditions

We present a detailed investigation of the changes in the local structure and chemical disorder induced by controlled potential cycling in Pt3±δCo nanoparticles used as a catalyst in the proton exc...