Effect Of Structural Disorder Research Articles

Observation of critical magnetic behavior in 2D carbon based composites.

Two dimensional (2D) carbonaceous materials such as graphene and its derivatives, e.g., graphdiyne, have enormous potential possibilities in major fields of scientific research. Theoretically, it has been proposed that the perfect atomic lattice arrangement of these materials is responsible for their outstanding physical and chemical properties, and also for their poor magnetic properties. Experimentally, it is difficult to obtain a perfect atomic lattice of carbon atoms due to the appearance of structural disorder. This structural disorder is generated during the growth or synthesis of carbon-related materials. Investigations of structural disorder reveal that it can offer both advantages and disadvantages depending on the application. For instance, disorder reduces the thermal and mechanical stability, and deteriorates the performance of 2D carbon-based electronic devices. The most interesting effect of structural disorder can be seen in the field of magnetism. Disorder not only creates magnetic ordering within 2D carbon materials but also influences the local electronic structure, which opens the door for future spintronic devices. Although various studies on the disorder induced magnetism of 2D carbon materials are available in the literature, some parts of the above field have still not been fully exploited. This review presents existing work for the future development of 2D carbon-based devices.

Towards a white-emitting phosphor Ca10V6O25 based material

To achieve a stable material capable of white-light emission, we fabricated Ca10V6O25 by both co-precipitation (CP) and microwave-assisted hydrothermal (MAH) methods at different temperatures. The effects of structural disorder at a short-range (Raman spectra), medium-range (UV–vis spectra), and long-range (X-ray diffraction) on the material structure and its effect on optical properties were investigated. Both CP and the MAH methods were efficient for obtaining pure Ca10V6O25 material with different morphologies. Significant changes in morphology and degree of structural order and disorder were found to affect the photoluminescence (PL) properties. All samples exhibited a broadband PL spectrum, characteristic associated to charge transfer processes of the [VO4]3- group, as well as transitions that occurred in the energy levels located within the band gap. The samples obtained by the MAH method at temperatures of 100 °C and 120 °C exhibited a lower structural disorder (at long- and short-ranges), the CIE chromaticity coordinates were located in the white region, MAH100 (x = 0.311 and y = 0.348) and MAH120 (x = 0.350 and y = 0.368). Furthermore, we conducted a detailed study of temperature dependence of PL spectra. All samples displayed decreased luminescence intensity as temperatures increased and low values of activation energy (approximately 2 meV). Finally, the as-synthetized Ca10V6O25 material has interesting properties for possible applications as a white-emitting phosphor under ultraviolet excitation.

Stress response of 2D silica under quasi‐static tension

AbstractWe use classical molecular dynamics simulations to generate topologically different models of vitreous 2D silica, all of which are subjected to quasi‐static tensile loading until fracture occurs. We demonstrate the effects of structural disorder on the material behaviour of 2D silica. For each sample, we determine the network structure by identifying the relative count of single rings and so‐called ring triplets each of which composed of three adjacent rings that share a common corner. In each sample, we spatially detect the first local atomic‐scale rearrangement during deformation and correlate it to the ring triplet involved.

Influence of interfacial structural disorder and/or chemical interdiffusion on thermal boundary conductance for Ti/Si and Au/Si couples

This work aims at experimentally assessing the effect of structural disorder and/or chemical interdiffusion on thermal boundary conductance (TBC) at metal/dielectric interfaces. To this end, the TBC of Au/Si and Ti/Si interfaces was measured by time domain thermoreflectance in the as-deposited state and after various heat treatments. Transmission electron microscopy (TEM) was used to determine the structure of the interface for each heat treatment condition. The TBC at the Au/Si interface was found to be highest in the as-deposited state and to be somewhat reduced after heat treatments. TEM images showed that the highest TBC was obtained when the interface contained a disordered transition layer with some degree of interdiffusion as present in the as-deposited state. Heat treatments led to the separation of species and to more abrupt interfaces with lower TBC. Whether this change in TBC was linked to disorder or to interdiffusion could not be distinguished. The TBC at the Ti/Si interfaces was observed to decrease with the heat treatment duration. TEM investigations revealed the presence of a thin disordered layer that did not evolve much with heat treatments. The evolution of the TBC was hence rationalized by interdiffusion facilitated by heat treatments that most likely modified the diffusion zone thickness and chemical composition, as well as the disordered layer's chemical composition. These changes result in modified interfacial properties, which ultimately affect the TBC. A quantitative exploration of the TBC dependence on the composition was not possible in this work, due to the extreme thinness of the regions under consideration preventing any reliable STEM-energy dispersive x-ray measurement.

Effect of structural disordering on magnetic and magneto-optical properties of Fe3Si

The electronic, magnetic, transport, and magneto-optical properties of the $D{0}_{3}$ and amorphous $\mathrm{F}{\mathrm{e}}_{3}\mathrm{Si}$ are investigated by using the first-principles calculations. A strong correlation between local magnetization and atomic arrangement is established. The amorphization significantly alters the spin polarization and the magneto-optical Kerr rotation spectrum but has a little influence on anomalous Hall conductivity. Analyses in band structures and interband matrix elements provide clear insights for the understanding of these results.

Structural disorder and short-range order in full Heusler alloys Fe2VAl and Co2CrAl from first principles calculations

Heusler alloys are intensively studied and applied in various spintronic devices. First principles calculations of their electronic structure allow to predict promising compounds with high spin polarization. However the theoretical predictions usually substantially deviate from experimental data. One of the reason is incorrect structural models used in the calculations. Heusler alloys are apt to form various disordered modifications with high concentration of antisite defects. In this paper we considered the effects of structural order and disorder on the electronic structure, stability and magnetic properties of full Heusler alloys Fe2VAl and Co2CrAl. The ordered Fe2VAl is non-magnetic narrow-gap semiconductor, the ordered Co2CrAl is a ferromagnet with metal behavior for majority spin band and narrow-gap semiconductor for minority one. When disordering Fe2VAl becomes a ferromagnetic metal. Co2CrAl loses minority band gap and its spontaneous magnetization reduces by 32%. Introduction of short range order in the disordered structure by increasing the portion of clusters specific for bcc structure further raised the magnetization in Fe2VAl and did not change it in Co2CrAl.

Effect of structural and thermal disorder on the optical band gap energy of Cr2O3 nanoparticles

Chromium oxide (Cr2O3) nanoparticles have been synthesized at different pH values by using co-precipitation technique. As prepared nanoparticles are then structurally characterized using x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscope (HR-TEM), fourier transform infrared (FT-IR) and micro-Raman spectroscopy. XRD, micro-Raman, HRTEM and fourier transform infrared (FT-IR) spectra confirmed the formation of single phase rhombohedral structure of Cr2O3 nanoparticles. Optical properties of Cr2O3 nanoparticles have been studied using UV–vis absorption spectroscopy. Tauc’s relation was used to determine the optical band gap energy of Cr2O3 nanoparticles and found to be decreasing with the increase of crystallite size. This phenomenon is explained in terms of Urbach energy. Urbach energy has been calculated to account for disorder and found to be increasing from 569 to 934 meV as pH value increased from 6 to 10, respectively. Debye Waller factor and electron-phonon interactions of Cr2O3 nanoparticles have also been investigated in this present study, to explain observed discrepancy between experimental and theoretical determined optical band gap values.

Magnetic Properties, Magnetocaloric Effect, and Critical Behavior of Gd – Co – Ge Amorphous Ribbons

The effect of structural disordering on the magnetic properties and magnetocaloric effect of amorphous (Gd4Co3)1–xGex (x = 0, 0.05, 0.10, 0.15) alloys is studied. The structure of the ribbons after melt-spinning is determined using an x-ray diffractometer. The thermal analysis is performed with the help of a differential scanning calorimeter. The temperature of the start of crystallization is determined. The magnetic properties are measured in a PPMS-9 system. The Curie temperature and the temperature dependence of the magnetization are determined. Different models are used for describing the critical exponents of the magnetic phase transitions.

Strain induced disordered phonon modes in Cr doped PrFeO3

Room temperature optical absorption spectroscopy (OAS) and Raman spectroscopy measurements have been carried out in order to understand the effect of structural disorder on the electronic and phononic states. For this purpose, polycrystalline samples of Cr doped PrFeO3 have been prepared via wet chemical route. OAS analysis suggests the systematic scaling of electronic disorder with Cr doping; whereas, shifting in Raman line shapes and an increase in Raman line width has been observed with Cr doping. X-ray diffraction analysis clearly suggests the increase in structural disorders in the form of crystallographic strain with Cr doping, which is consistent with the broadening in Raman line shapes. The major contribution to Raman line width has been understood in terms of temperature independent terms i.e. structural disorder induced by doping. The generation of a new phonon mode at ~510 cm−1 has been observed and understood as a disorder phonon mode due to strain induced structural disorder. Moreover, a systematic correlation between crystallographic strain, Raman line width, disordered parameter (σ) and Urbach energy has been observed, which implies that structural disorder affects phononic as well as electronic states of the system. Such comparative study allows us to find the correlation between densities of tail states, structural disorders and anharmonic effects probed by Raman spectroscopy.

Effect of structural disorder on the electronic and phononic properties of Hf doped BaTiO3

The classical ferroelectric material BaTiO3 has been doped with large cation i.e., Hf at Ti site in order to understand the effect of structural disorder in electronic and phononic state. The Raman spectroscopy measurement on these samples indicates increase in the structural disorder with Hf doping. The detail analysis of the Raman spectroscopy data clearly suggests the appearance of new Raman mode at ~ 780 cm−1 and the presence of an asymmetry in almost all Raman modes. The appearance of new Raman mode has been attributed due to the structural disorder induced phonon modes; and this is further confirmed using laser irradiation studies. Additionally, it has been observed that the intensity of this new phonon mode increases systematically with Hf doping; indicating increase in the phononic disorder. It has been observed that the line shape Raman phonon modes show significant asymmetry and this asymmetry along with the full peak width at half maxima (FWHM) of Raman phonon mode shows systematic variation with Hf doping. The observed asymmetric Raman line profile has been analysed through Fano model of electron–phonon coupling which suggests an increase in the electron–phonon coupling with Hf doping. In order to get further insight on increase in the electron–phonon coupling near band edge optical absorption spectroscopy measurements has been carried out and value of electronic disorder in the form of Urbach energy has been estimated and the same is observed to scale with Hf doping. Thus, the systematic increase in the intensity of disorder phonon mode and that of electronic disorder has been observed. This suggests that structural disorder not only affects phonons but electronic state of the system as well. Thus, it appears that the increase in the width of electronic and phononic disorder may overlap in energy scale and may be responsible for the observed increase in the electron–phonon coupling parameter as estimated through Fano equation.

Crystal structure model development for soil clay minerals – II. Quantification and characterization of hydroxy-interlayered smectite (HIS) using the Rietveld refinement technique

The acidic weathering process of soils is a worldwide problem. In this process, Al3+ is dissolved from silicates and intercalated into swellable clay minerals by replacing exchangeable cations such as Na+ or Ca2+. Al3+ polymerizes in the interlayer regions of the clay minerals to form fixed oligomers, which significantly reduces the clay minerals swellability and cation exchange, and hence, the soil fertility. The layer silicates with fixed (Al) oligomers in the interlayer are known as hydroxy-interlayered minerals, such as hydroxy-interlayered smectite (HIS), or hydroxy-interlayered vermiculite (HIV). These phases have been recognized for many years, but it is still problematic to adequately characterize the details of their structure and to determine their proportion in soils, based on X-ray diffraction (XRD), which is the most common method for mineral quantification. In the present study, two crystal structure models are used to allow characterization and quantitative determination of HIS in artificial and natural soils, using the Rietveld refinement technique based on XRD. Both models are identical regarding the 2:1 layer and the description of the hydroxy-interlayering, but differ in the effect imposed by environmental conditions. The first model describes the smectite in the ethylene glycol saturated state (≈17 Å), commonly used by clay scientists as a diagnostic intercalate for swellable smectitic or vermiculitic layers in pure smectite or vermiculite or interstratifications. The second model describes the smectite in the air-dried (AD) state including the collapsed state (≈10 Å), one-water layer state (≈12.5 Å), and two-water layer state (≈15 Å). Both models are used to fit XRD patterns obtained from samples with preferred orientation and from XRD random powder specimens, each including structural disorder effects. The models provide plausible refinement results with respect to crystallographic parameters and quantitative proportions. The degree of hydroxy-interlayering gives an estimate of how many exchangeable cations of the smectite were replaced by fixed Al oligomers that inhibit expandability. This value corresponds to calculated values within a range of precision of ≤15% mol/mol. Physical mixtures of HIS with clinochlore, muscovite, quartz, and albite were quantified using the proposed crystal structure model. Results showed that the HIS model delivers reliable quantification results (deviations from actual values ≤3% w/w) which may be applied also for natural soil.

The Effect of Anti-Site Disorder on Structural and Magnetic Properties of Ni–Co–Mn–In Alloys: <italic>Ab Initio</italic> and Monte Carlo Studies

In this paper, we report on the effect of partial structural B2-like disorder on martensitic transformation and thermomagnetization curves in Ni–Co–Mn–In alloy by using the theoretical approach involving first principles and Monte Carlo methods. In case of ground-state electronic calculations, the off-stoichiometric composition was treated by using both supercell and coherent potential approaches. It is found that the increase of a structural disorder degree leads to decrease the energy difference between austenite and martensite phases, which corresponds to a decrease in the martensitic transformation temperature according to $\Delta E \approx k_{B}T_{m}$ . Besides, the magnetic exchange interaction constants for both martensite and austenite are slightly weakened by influence of structural disorder. Using calculated exchange coupling constants in the effective Potts–Blume–Emery–Griffiths Hamiltonian, a set of magnetization curves for the studied system is simulated. It is shown that the account of disorder results in a decrease in the magnetization value around the magnetostructural transformation. Theoretical results reproduce well the experimental ones.

Effects of polydispersity and disorder on the mechanical properties of hydrated silicate gels

The colloidal calcium–silicate–hydrate (C–S–H) gel largely controls the strength of concrete. However, little remains known about how the structural features of the C–S–H gel control its mechanical properties. Here, based on coarse-grained mesoscale simulations, we investigate the effect of grain polydispersity and structural disorder on the nanomechanics of C–S–H. Our simulations offer a good agreement with nanoindentation data over a large range of packing density values. We show that, at constant packing density, stiffness and hardness are not affected by the polydispersity in grain sizes. In contrast, the level of disorder is found to play a critical role. We demonstrate that, in contrast to the case of ordered C–S–H models, the elastic response of disordered C–S–H gels is governed by the existence of stress heterogeneity and nanoyielding within its structure. These results highlight the intrinsically disordered nature of C–S–H and the crucial role of order and disorder in controlling gels’ mechanical properties.

Effect of thermally induced structural disorder on the chemical durability of International Simple Glass

While the influence of silicate oxide glass composition on its chemical durability is increasingly known, the contribution of structure only is less well understood, yet is crucial for an accurate description of aqueous alteration mechanisms. The effect of structural disorder can be investigated by varying the thermal history of the glass. Furthermore, the structural changes generated by self-irradiation in nuclear glasses can be compared with those induced by fast quenching. In the context of deep geological disposal of vitreous matrices, it is then challenging to address the structural impact on glass durability. Here, a borosilicate glass, the International Simple Glass, was fiberized to obtain a rapidly quenched sample. The quenching rate and fictive temperature were evaluated from in situ Raman and Brillouin spectroscopies. Multinuclear nuclear magnetic resonance was used to obtain insight into the effect of quenching on the pristine and altered glass structure. Higher bond angle distribution and lower mixing of alkalis were observed in the fast quenched glass. Some of AlO4 groups are then Ca-compensated, while a part of BO4 is transformed into BO3 units. The structural modifications increase the hydrolysis of the silicate network occurring in the forward rate regime at 90 °C by a factor of 1.4–1.8 depending on the pH value. Residual rate regime is similarly affected, more significantly at the beginning of the experiments conducted in silica saturated solutions. These findings prove that the reactivity of glass remains controlled by its structure under the various alteration regimes.

Ordered-Disordered BaZrO3-δ Hollow Nanosphere/Carbon Dot Hybrid Nanocomposite: A New Visible-Light-Driven Efficient Composite Photocatalyst for Hydrogen Production and Dye Degradation.

Perovskites form an interesting class of photocatalytic compounds because of their chemical stability and exotic chemistry. Although barium zirconates have been known for a long time, their photocatalytic study in the literature is very limited. Herein, we have studied the effect of structural disorder, oxygen vacancies and carbon dots (CDs) on photocatalytic activity of BaZrO3−δ (BZO) hollow nanospheres. High alkaline conditions during hydrothermal synthesis lead to the formation of disordered states as well as oxygen vacancies in BZO and create midgap states within the band gap of BZO. The midgap states further shift its absorption onset toward visible light and their presence and effects have been proved by ultraviolet–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance analysis. A composite that consists of CDs shows upconversion photoluminescence and charge-carrier transfer properties to enhance the light absorption of a photocatalyst and its activity. The photocatalytic efficiency of the compounds were examined by H2 evolution and the degradation of methylene blue (MB) dye. In this study, loading of 3 wt% CDs on BZO shows the highest hydrogen evolution efficiency (670 μmol/h/g) with an apparent quantum yield of ∼4% and the highest MB dye degradation efficiency (∼90%) among all synthesized composites. The synergistic effect of increased visible light absorption along with enhanced photogenerated charge-carrier transfer efficiency in the presence of CDs and oxygen vacancies in BZO contributes to the enhanced photocatalytic efficacy of hybrid nanomaterials under visible light irradiation.

Critical Role of the Chemical Environment of Interlayer Na Sites: An Effective Way To Improve the Na Ion Electrode Activity of Layered Titanate.

The chemical environments of the interlayer Na sites of layered titanate are finely controlled by the intercalation of n-alkylamine with various alkyl chain lengths to explore an effective way to improve its electrode functionality for sodium-ion batteries (SIBs). The n-alkylamine intercalation via ion-exchange and exfoliation-restacking routes allows the modification of in-plane structures of layered titanate to be tuned. Among the present n-alkylamine-intercalates, the n-pentylamine-intercalated titanate shows the largest discharge capacity with the best rate characteristics, underscoring the critical role of optimized intracrystalline structure in improving the SIB electrode performance of layered titanate. The creation of turbostratic in-plane structure degrades the SIB electrode performance of layered titanate, indicating the detrimental effect of in-plane structural disorder on electrode activity. 23Na magic-angle spinning nuclear magnetic resonance spectroscopy demonstrates that the n-alkylamine-intercalated titanates possess two different interlayer Na+ sites near ammonium head groups/titanate layers and near alkyl chains. The intercalation of long-chain molecules increases the population of the latter site and the overall mobility of Na+ ions, which is responsible for the improvement of electrode activity upon n-alkylamine intercalation. The present study highlights that the increased population of interlayer metal sites remote from the host layers is effective in improving the electrode functionality of layered metal oxide for SIBs and multivalent ion batteries.

Effect of structural disorder on transport properties of LaNiO3 thin films

We have deposited LaNiO3 thin films on LaAlO3 (001), SrTiO3 (001), and Si (001) substrates using the pulsed laser deposition technique. Depositions were carried out at various substrate temperatures ranging from 0 to 800 °C. The effects of lattice mismatch and structural disorder on the transport properties of films deposited on various substrates and at different substrate temperatures are reported. X-ray diffraction confirms a highly c-axis oriented growth of LaNiO3 films on all the substrates at substrate temperatures of 600 and 800 °C, while at lower substrate temperatures deposited films are amorphous. Emergence of a new Raman mode indicates symmetry lowering in all the deposited crystalline films. Hardening of the Eg(3) (∼400 cm−1) mode is also observed with the rise of in-plane compressive strain. Resistivity curves for films on Si show a semiconducting behaviour and follow a variable range hopping mechanism. Crystalline films on LaAlO3 and SrTiO3 exhibit a metallic character along with a low-temperature resistivity upturn, which is attributed to the contribution of self-localization to resistivity at low temperatures as indicated by magnetotransport measurements.

Effect of structural disorder and Coulomb interactions in the superconductor-insulator transition applied to boron doped diamond

The effect of disorder, both structural (non-diagonal) and on-site (diagonal), is studied through the inhomogeneous Bogoliubov-de Gennes (BdG) theory in narrow-band disordered superconductors with a view towards understanding superconductivity in boron doped diamond (BDD) and boron-doped nanocrystalline diamond (BNCD) films. We employ the attractive Hubbard model within the mean field approximation, including the short-range Coulomb interaction between holes in the narrow acceptor band. We study substitutional boron incorporation in a triangular lattice, with disorder in the form of random potential fluctuations at the boron sites. The role of structural disorder was studied through non-uniform variation of the tight-binding coupling parameter where, following experimental findings, we incorporate the concurrent increase in structural disorder with increasing boron concentration. We illustrate stark differences between the effects of structural and on-site disorder and show that structural disorder has a much greater effect on the density of states, mean pairing amplitude and superfluid density than on-site potential disorder. We show that structural disorder can increase the mean pairing amplitude while the spectral gap in the density of states decreases with states eventually appearing within the spectral gap for high levels of disorder. This study illustrates how the effects of structural disorder can explain some of the features found in superconducting BDD and BNCD films such as a tendency towards saturation of the Tc with boron doping and deviations from the expected BCS theory in the temperature dependence of the pairing amplitude and spectral gap.

A Review on Recent Developments and Prospects for the Oxygen Reduction Reaction on Hollow Pt-alloy Nanoparticles.

Due to their interesting electrocatalytic properties for the oxygen reduction reaction (ORR), hollow Pt-alloy nanoparticles (NPs) supported on high-surface-area carbon attract growing interest. However, the suitable synthesis methods and associated mechanisms of formation, the reasons for their enhanced specific activity for the ORR, and the nature of adequate alloying elements and carbon supports for this type of nanocatalysts remain open questions. This Review aims at shedding light on these topics with a special emphasis on hollow PtNi NPs supported onto Vulcan C (PtNi/C). We first show how hollow Pt-alloy/C NPs can be synthesized by a mechanism involving galvanic replacement and the nanoscale Kirkendall effect. Nickel, cobalt, copper, zinc, and iron (Ni, Co, Cu, Zn, and Fe, respectively) were tested for the formation of Pt-alloy/C hollow nanostructures. Our results indicate that metals with standard potential -0.4<E<0.4 V (vs. the normal hydrogen electrode) and propensity to spontaneously form metal borides in the presence of sodium borohydride are adequate sacrificial templates. As they lead to smaller hollow Pt-alloy/C NPs, mesoporous carbon supports are also best suited for this type of synthesis. A comparison of the electrocatalytic activity towards the ORR or the electrooxidation of a COads monolayer, methanol or ethanol of hollow and solid Pt-alloy/C NPs underlines the pivotal role of the structural disorder of the metal lattice, and is supported by ab initio calculations. As evidenced by accelerated stress tests simulating proton-exchange membrane fuel cell cathode operating conditions, the beneficial effect of structural disorder is maintained on the long term, thereby bringing promises for the synthesis of highly active and robust ORR electrocatalysts.

A Physics-Based Compact Model for Transition-Metal Dichalcogenides Transistors With the Band-Tail Effect

Due to structural disorder effects, variable range hopping (VRH) transport via band-tail states has been widely observed in the transition-metal dichalcogenide field-effect transistor (TMD FET). However, this significant mechanism has not been incorporated into existing compact models. In this letter, a continuous physics-based compact model considering VRH in TMD FET is developed. Key parameters are extracted by calibration to experimental molybdenum disulfide FET. The voltage dependent carrier density and temperature dependent current characteristics are physically predicted by utilizing the general percolation theory and generalized Einstein relation. Our model is validated by the good agreement between the simulation and experimental results. Furthermore, the relationship between the disorder effects and circuit-level performances are presented. This letter is significant for material engineering and device optimization of TMD FET.