Effect Of Structural Disorder Research Articles

Unraveling the connection of electronic and phononic structure with mechanical properties of commercial AZ80 alloy

Magnesium alloys, particularly in the aluminum-zinc (AZ) series, are widely recognized for their remarkable strength-to-weight ratio. We performed electronic structure, lattice dynamics, and mechanical properties of the AZ80 alloy using first-principles density-functional theory. The influence of dilute alloying by Al/Zn was observed in electronic-structure of AZ80 through hybridization of Mg-(s,p) with Al-p/Zn-d states. The Allen’s electronegativity difference between Mg and Al/Zn was found to induce charge transfer mechanism that provides solid-solution strengthening and ductility, in agreement with experiments. The electronic and phononic band-structure was unfolded onto the primitive unit cell of pure Mg to provide key information related to structural distortions and disorder effects. Finally, the dynamic and mechanical stability of AZ80 were confirmed by phonons and Born-Huang criteria, respectively. Collectively, this study provides valuable insights into the fundamental properties of lightweight commercial grade AZ80, essential for application-oriented design of Mg alloys.

Charged Exciton Generation by Curvature-Induced Band Gap Fluctuations in Structurally Disordered Two-Dimensional Semiconductors.

Curvature is a general factor for various two-dimensional (2D) materials due to their flexibility, which is not yet fully unveiled to control their physical properties. In particular, the effect of structural disorder with random curvature formation on excitons in 2D semiconductors is not fully understood. Here, the correlation between structural disorder and exciton formation in monolayer MoS2 on SiO2 was investigated by using photoluminescence (PL) and Raman spectroscopy. We found that the curvature-induced charge localization along with band gap fluctuations aid the formation of the localized charged excitons (such as trions). In the substrate-supported region, the trion population is enhanced by a localized charge due to the microscopic random bending strain, while the trion is suppressed in the suspended region which exhibits negligible bending strain, anomalously even though the dielectric screening effect is lower than that of the supported region. The redistribution of each exciton by the bending strain leads to a huge variation (∼100-fold) in PL intensity between the supported and suspended regions, which cannot be fully comprehended by external potential disorders such as a random distribution of charged impurities. The peak position of PL in MoS2/SiO2 is inversely proportional to the Raman peak position of E12g, indicating that the bending strain is correlated with PL. The supported regions exhibit an indirect portion that was not shown in the suspended regions or atomically flat substrates. The understanding of the structural disorder effect on excitons provides a fundamental path for optoelectronics and strain engineering of 2D semiconductors.

Insights into the Jahn‐Teller Effect in Layered Oxide Cathode Materials for Potassium‐Ion Batteries

AbstractPotassium‐ion batteries (PIBs) have attracted increasing interest as promising alternatives to lithium‐ion batteries (LIBs) in large‐scale electrical energy storage systems due to the potential price advantages, abundant availability of potassium resources, and low standard redox potential of potassium. However, the pursuit of suitable cathode materials that exhibit desirable characteristics such as voltage platforms, high capacity, and long cycling stability is of utmost importance. Recently, layered transition‐metal oxides for PIBs offer great potential due to their high theoretical capacity, suitable voltage range, and eco‐friendliness. Nevertheless, the progress of KxMO2 cathodes in PIBs faces obstacles due to the detrimental effects of structural disorder and irreversible phase transitions caused by the Jahn‐Teller effect. This review provides a brief description of the origin and mechanism of the Jahn‐Teller effect, accompanied by the proposed principles to mitigate this phenomenon. In particular, the current status of KxMO2 cathodes for PIBs, is summarized highlighting the challenges posed by the Jahn‐Teller effect. Furthermore, promising strategies, such as composition modulation, synthesis approaches, and surface modification, are proposed to alleviate and suppress the Jahn‐Teller effect. These strategies offer valuable insights into the prospects of innovative cathode materials and provide a foundation for future research in the field of PIBs.

Effect of structural disorder on the modification of V–V and V–O bond lengths at the metal-dielectric phase transition in VO2 thin films

The dynamics of anomalous changes in the microstructure, as well as optical and electrical properties of microcrystalline VO2 thin films on Si substrates during a reversible temperature-induced metal-insulator phase transition (MIT), were studied by high-resolution X-ray diffractometry (XRD), micro-Raman spectroscopy, and resistivity measurements. Temperature-dependent XRD studies of microcrystalline VO2 films revealed the coexistence of monoclinic VO2(M1) and tetragonal VO2(R) structural phases near the MIT, attributable to deformation inhomogeneities and grain size variations. It was determined that inhomogeneous microstructural distortion is the primary factor influencing the MIT in strained VO2 films. Concurrently, significant variations in the resistivity hysteresis were observed in association with the phase transitions. The structural phase transition (SPT) in VO2 films was investigated via temperature-dependent micro-Raman spectroscopy, which elucidated the microstructural influence on the MIT. As the VO2(M1) temperature approached the critical SPT temperature (340 K), the narrow Raman spectrum of the insulating phase transitioned into a broadband spectrum characteristic of the metallic VO2(R) phase, marked by four pronounced peaks at approximately 230 cm−1 (B1g), 400 cm−1 (Eg), 550 cm−1 (A1g), and 635 cm−1 (B2g). The analysis of the V–V and V–O vibrational modes in VO2 indicates that alterations in the V–V and V–O bond lengths are crucial to the temperature-driven SPT from the low-temperature monoclinic VO2(M1) phase to the high-temperature tetragonal VO2(R) phase. The observed hysteretic temperature dependence of the Raman intensities for V–V and V–O modes shows a quantitative correlation with the resistivity measurements of the VO2 films, providing insights into the interplay between the SPT and the MIT. The results obtained are pivotal for comprehending the structural and electronic behaviors of nanoscale films and hold significant implications for their application in functional devices.

Effects of Structural Radiation Disorder in the Near-Surface Layer of Alloys Based on NbTiVZr Compounds Depending on the Variation of Alloy Components

This research investigated how changes in the composition of Nb–Ti–V–Zr-based alloys affect their resistance to radiation damage and the preservation of strength characteristics when exposed to the heavy ions Kr15+ and Xe23+. These heavy ions simulate the impact of nuclear fuel fission fragments on the material. The primary objective of this study was to explore how variations in alloy components influence radiation resistance and the retention of alloy strength properties. Accumulation of radiation defects can potentially lead to embrittlement and a decrease in resistance to external factors during operation. An analysis of the X-ray diffraction data obtained from the initial alloy samples, in relation to the variations in the number of components, revealed that an increase in the number of components leads to the formation of a denser crystal structure. Additionally, this resulted in the emergence of a dislocation strengthening factor associated with changes in crystallite size. Concurrently, when assessing changes in the strength characteristics of the irradiated alloys, it was observed that the NbTiV and NbTiVZr alloys demonstrated the highest resistance to strength property degradation, specifically a 2.5- to 5-fold increase in resistance against a significant decrease in hardness. It was confirmed that the significant factor contributing towards the enhancement and preservation of the structural and strength properties is the dislocation strengthening mechanism. An increase in dislocation strengthening effectively enhances resistance against destructive embrittlement, particularly when exposed to high-dose irradiation.

Effect of structural disorder on the oxidation of Zr-based amorphous alloys: A focused review

Structural disordering leads to outstanding mechanical properties of amorphous alloys. Many properties are strongly related to formation of surface oxide layers. An in-depth understanding of effect of structural disordering of amorphous alloys on oxide evolution is essential for applications. This paper presents a review of recent comparative oxidation studies of Zr-based amorphous and single-phase crystalline counterpart alloys. Three representative model alloy systems are selected: Zr–Cu and Zr–Al representing alloys with components of different and similar oxygen affinities, respectively, and Zr–Cu–Al representing multi-component alloys. In combination with molecular dynamic simulations, the fundamental role of the structural disordering of parent alloys in the oxidation processes is revealed. The oxidation of Zr–Cu–Al–Ni amorphous alloys at the supercooled liquid temperature region is further reviewed to clarify the relationship between oxidation and substrate crystallization.

Atomistic Insights into Ultrafast SiGe Nanoprocessing.

Controlling ultrafast material transformations with atomic precision is essential for future nanotechnology. Pulsed laser annealing (LA), inducing extremely rapid and localized phase transitions, is a powerful way to achieve this but requires careful optimization together with the appropriate system design. We present a multiscale LA computational framework that can simulate atom-by-atom the highly out-of-equilibrium kinetics of a material as it interacts with the laser, including effects of structural disorder. By seamlessly coupling a macroscale continuum solver to a nanoscale superlattice kinetic Monte Carlo code, this method overcomes the limits of state-of-the-art continuum-based tools. We exploit it to investigate nontrivial changes in composition, morphology, and quality of laser-annealed SiGe alloys. Validations against experiments and phase-field simulations as well as advanced applications to strained, defected, nanostructured, and confined SiGe are presented, highlighting the importance of a multiscale atomistic-continuum approach. Current applicability and potential generalization routes are finally discussed.

Compositional and Structural Disorder in Two-Dimensional AIIIBVI Materials

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys.

Disorder effect on intersubband optical absorption of n-type δ-doped quantum well in GaAs

The inevitable structural disorder associated with the fluctuation of the applied external electric field, laser intensity, and bidimensional density in the low dimensional quantum system can affect noticeably optical absorption properties and the related phenomena. In this work, we study the effect of structural disorder on the optical absorption properties in delta-doped quantum wells (DDQWs). Starting from effective mass approximation and the Thomas-Fermi approach as well as using the matrix density, the electronic structure and the optical absorption coefficients of DDQWs are determined. It is found that the optical absorption properties depend on the strength and the type of structural disorder. Particularly, the bidimensional density disorder suppresses strongly the optical properties. Whilst, the disordered external applied electric field fluctuates moderately in the properties. In contrast, the disordered laser holds absorption properties unalterable. So, our results specify that to have and preserve good optical absorption properties in DDQWs, requires precise control of the bidimensional. Besides, the finding may improve the understanding of the impact of the disorder on the optoelectronic properties based on DDQWs.

Thermal conductivity of glasses: first-principles theory and applications

Predicting the thermal conductivity of glasses from first principles has hitherto been a very complex problem. The established Allen-Feldman and Green-Kubo approaches employ approximations with limited validity—the former neglects anharmonicity, the latter misses the quantum Bose-Einstein statistics of vibrations—and require atomistic models that are very challenging for first-principles methods. Here, we present a protocol to determine from first principles the thermal conductivity κ(T) of glasses above the plateau (i.e., above the temperature-independent region appearing almost without exceptions in the κ(T) of all glasses at cryogenic temperatures). The protocol combines the Wigner formulation of thermal transport with convergence-acceleration techniques, and accounts comprehensively for the effects of structural disorder, anharmonicity, and Bose-Einstein statistics. We validate this approach in vitreous silica, showing that models containing less than 200 atoms can already reproduce κ(T) in the macroscopic limit. We discuss the effects of anharmonicity and the mechanisms determining the trend of κ(T) at high temperature, reproducing experiments at temperatures where radiative effects remain negligible.

Extending the diatom's color palette: non-iridescent, disorder-mediated coloration in marine diatom-inspired nanomembranes.

The intricate, siliceous exoskeleton of many marine diatoms (single-celled phytoplankton) is decorated with an array of sub-micron, quasi-ordered pores that are known to provide protective and multiple life-sustaining functions. However, the optical functionality of any given diatom valve is limited because valve geometry, composition, and ordering are genetically programmed. Nonetheless, the near- and sub-wavelength features of diatom valves provide inspiration for novel photonic surfaces and devices. Herein, we explore the optical design space for optical transmission, reflection, and scattering in diatom-like structures by computationally deconstructing the diatom frustule, assigning and nondimensionalizing Fano-resonant behavior with configurations of increasing refractive index contrast (Δn), and gauging the effects of structural disorder on the resulting optical response. Translational pore disorder, especially in higher-index materials, was found to evolve Fano resonances from near-unity reflection and transmission to modally confined, angle-independent scattering, which is key to non-iridescent coloration in the visible wavelength range. High-index, frustule-like TiO2 nanomembranes were then designed to maximize backscattering intensity and fabricated using colloidal lithography. These synthetic diatom surfaces showed saturated, non-iridescent coloration across the visible spectrum. Overall, this diatom-inspired platform could be useful in designing tailored, functional, and nanostructured surfaces for applications in optics, heterogeneous catalysis, sensing, and optoelectronics.

Ground-State Spin Dynamics in d1 Kagome-Lattice Titanium Fluorides.

Many quantum magnetic materials suffer from structural imperfections. The effects of structural disorder on bulk properties are difficult to assess systematically from a chemical perspective due to the complexities of chemical synthesis. The recently reported S = 1/2 kagome lattice antiferromagnet, (CH3NH3)2NaTi3F12, 1-Ti, with highly symmetric kagome layers and disordered interlayer methylammonium cations, shows no magnetic ordering down to 0.1 K. To study the impact of structural disorder in the titanium fluoride kagome compounds, (CH3NH3)2KTi3F12, 2-Ti, was prepared. It presents no detectable structural disorder and only a small degree of distortion of the kagome lattice. The methylammonium disorder model of 1-Ti and order in 2-Ti were confirmed by atomic-resolution transmission electron microscopy. The antiferromagnetic interactions and band structures of both compounds were calculated based on spin-polarized density functional theory and support the magnetic structure analysis. Three spin-glass-like (SGL) transitions were observed in 2-Ti at 0.5, 1.4, and 2.3 K, while a single SGL transition can be observed in 1-Ti at 0.8 K. The absolute values of the Curie-Weiss temperatures of both 1-Ti (-139.5(7) K) and 2-Ti (-83.5(7) K) are larger than the SGL transition temperatures, which is indicative of geometrically frustrated spin glass (GFSG) states. All the SGL transitions are quenched with an applied field >0.1 T, which indicates novel magnetic phases emerge under small applied magnetic fields. The well-defined structure and the lack of structural disorder in 2-Ti suggest that 2-Ti is an ideal model compound for studying GFSG states and the potential transitions between spin liquid and GFSG states.

Role of ion beams and their energies in the properties of zinc tin phosphide thin films

Zinc tin phosphide (ZTP) is a promising low cost light sensing semiconductor material. The present study focuses on the effects of various ion beams having energies in the range of keV to MeV, on the structural, optical, and photo-response properties of ZTP thin films. Low energy ions (100 and 200 keV Al and Cu, 150 keV Fe and 60 keV Au ions) of fluences in the range from 1E13 to 1E16 ions/cm2 and high energy ions (80 MeV Si, 100 MeV Ni and 100 MeV Ag ions) from 1E11 to 6E13 ions/cm2 are used. The energy of ions (low or high) determine the changes in the ion-induced defects, structural disorder and recrystallization effects leading to modification in the structural quality, the evolution of microstructure, variation in the optical band gap (from 1.60 to 1.82 eV), and the photo-responsivity to red light up to 0.66 mA/W. The photo-responsivity of the films enhances for 150 keV Fe, 60 keV Au, 80 MeV Si and 100 MeV Ni ions and reduces for 100 and 200 keV Al and Cu and 100 MeV Ag ions. These changes are strongly correlated with the electronic energy loss of the ions in the films. The study demonstrates the applicability of low and high energy ions to improve the photo-response and also reveals the possibility to estimate the extent of its progress in ZTP and other light-sensing materials relevant for photo-detector and solar cell applications.

Electronic structure, magnetic, transport, and optical properties of bulk and film Fe2CrGa Heusler alloy. Effect of structural disorder

Magnetic, transport, and optical properties of thin film and bulk Fe2CrGa alloy samples with different types of atomic order were experimentally investigated. The obtained data were discussed in terms of first-principle calculation results made for the stoichiometric Fe2CrGa alloy with different types of atomic order and disorder. An ultimate atomic disorder in Fe2CrGa alloy films was obtained by employing vapor quenching deposition onto substrates cooled by liquid nitrogen. Annealing of as-quenched Fe2CrGa alloy films causes their crystallization at Tann=750 K with the formation of the disordered A2-type structure, which is accompanied by the rapid growth of alloy resistivity in a narrow temperature range, formation of multi-phase magnetic structure and changes in the optical properties. Crystalline bulk and film Fe2CrGa alloy samples show the dome-like temperature dependence of the resistivity with maximums near their Curie temperatures and explained in terms of competition between negative with temperature contribution from highly resistive media and positive from the electron–magnon scattering. The big resemblance between calculated for Hg2CuTi type of atomic order and experimental optical conductivity spectra for annealed Fe2CrGa alloy films proves that Hg2CuTi type of atomic order is more probable for this alloy.

Effect of structural site disorder on the optical properties of Ag6+x(P1−xGex)S5I solid solutions

Effect of structural site disorder on the optical properties of Ag6+x(P1−xGex)S5I solid solutions

Effects of Crystalline Disorder on Interfacial and Magnetic Properties of Sputtered Topological Insulator/Ferromagnet Heterostructures

Thin films of Topological insulators (TIs) coupled with ferromagnets (FMs) are excellent candidates for energy-efficient spintronics devices. Here, the effect of crystalline structural disorder of TI on interfacial and magnetic properties of sputter-deposited TI/FM, Bi2Te3/Ni80Fe20, heterostructures is reported. Ni and a smaller amount of Fe from Py was found to diffuse across the interface and react with Bi2Te3. For highly crystalline c-axis oriented Bi2Te3 films, a giant enhancement in Gilbert damping is observed, accompanied by an effective out-of-plane magnetic anisotropy and enhanced damping-like spin-orbit torque (DL-SOT), possibly due to the topological surface states (TSS) of Bi2Te3. Furthermore, a spontaneous exchange bias is observed in hysteresis loop measurements at low temperatures. This is because of an antiferromagnetic topological interfacial layer formed by reaction of the diffused Ni with Bi2Te3 which couples with the FM, Ni80Fe20. For increasing disorder of Bi2Te3, a significant weakening of exchange interaction in the AFM interfacial layer is found. These experimental results Abstract length is one paragraph.

Grand canonical Monte Carlo simulation study on the effect of crystallinity and structural disorder on water sorption in geopolymers

A comparative study on water sorption by different components of the binder phase formed in geopolymerization was performed using the Grand Canonical Monte Carlo (GCMC) simulation method. Water sorption isotherms for crystalline, defective and amorphous model structures with Na+ exchangeable cations at temperatures of 298 K were obtained. The isosteric heats of adsorption of water in each structure were calculated. In addition, the distribution pattern of H2O molecules in the researched frameworks and the preferred sorption sites were also investigated. The GCMC results showed that the structural changes in the host framework significantly affect water sorption properties, leading to changes in water sorption capacity and nature of interactions with guest water molecules. The GCMC simulation results have provided useful information on the behavior of water confined in geopolymeric binder phase, which is difficult to observe experimentally, contributing to a better understanding of the mechanism of water adsorption in geopolymer-zeolite hybrid materials.

The effect of structural disorder on the hydrogen loading into the graphene/nickel interface

Hybrid materials composed by porous Ni foams coated by graphene appear appealing architectures to be applied in the field of hydrogen storage, where, due to the high surface-to-volume ratio of both components, are expected to be much more performant than their flat counterparts. In order to explore this possibility, in this study we have grown single layer graphene on nickel foams by chemical vapour deposition in ultra-high vacuum and have investigated the interaction with H atoms as a function of the temperature. By using high resolution C1s core level spectroscopy we found that nearly half of the graphene layer interacts with the support almost as strongly as with the flat ordered Ni substrate, whereas the other half is nearly free standing. Such dual electronic and structural coupling drives the hydrogenation of the graphene/foam interface. By using thermal programmed desorption combined with x-ray photoelectron spectroscopy we found that in the weakly interacting graphene regions, even at very low temperatures, H atoms easily intercalate below graphene, and enter in the bulk of the foam, from where they start to desorb around 180 K. This behaviour mimics what happens when dosing H atoms on the bare Ni foam. On the contrary, H intercalation below the strongly interacting graphene regions occurs only for temperatures around and above 200 K. The thermal desorption curves demonstrated that the presence of the graphene layer does not reduce the effectiveness of H loading in the bulk of the foam. On the other hand, it does not even increase significantly the stored amount with respect to the uncoated support, but contributes to stabilizing the stored hydrogen. Although the fundamental aspects of graphene/foam hydrogenation were here investigated in a regime far below the saturation of the bulk absorption, these measurements can be the starting point for further investigations aimed at establishing the ultimate storage capability of these hybrid nanostructured tanks.

Effects of structural disorder on the critical and hysteresis behaviours of nanoparticles with cubic structure

By means of Monte Carlo simulation, a systematic study is presented to reveal the effect of structural disorder on the critical and hysteresis behaviours of a Heisenberg ferromagnetic cubic structure. The atomic sites of the considered system are changed systematically from their regular positions by means of a disorder parameter, thereby allowing us to smoothly interpolate between regular and amorphous structures. We have shown that the critical temperature increases at threshold values of the disorder parameter. Moreover, we have found that the hysteresis loop’s area increases with increasing the structural disorder, thereby increasing the coercivity of the system.

Effect of Structural Disorder on the Physical Properties of the Pd Based Heusler Alloys: PdCoMnAl, Pd2CoAl and Pd2MnAl

In this manuscript, we investigate the effect of structural disorder on the physical properties of Pd-based Heusler alloys: PdCoMnAl, Pd2CoAl and Pd2MnAl using first-principles calculations. In fact, we are studying the structural properties of the equatorial quaternary Heusler alloy PdCoMnAl for three phases: type 1, type 2 and type 3, we have carried out this property to determine the most stable phases. The structural properties results show that the phase of type I, of this alloy is the most stable configuration. In addition, the band structures, and density of states calculations results show that this compound exhibits a half-metallic character with a 100% of spin polarization (SP) at the Fermi-level. The total magnetic moment of the Heusler compound is found to be 5.00 µB. Moreover, it is found that the Slater-Pauling is well described for this alloy. On the other hand, concerning total energy of the full Heusler Pd2YAl (Y = Co or Mn) alloys. It is found that such material in L21-type structure is always smaller than in the XA-type structure during the whole lattice variation variety and the L21-type structure is more energetically preferable for the both full alloys. In addition, the density of states at the Fermi level within the spin up and down states show the metallicity of these compounds. Our results show that the quaternary Heusler is a potential candidate for the spintronic applications.