Presence Of Compressive Strain Research Articles

Manipulating Electron Delocalization of Metal Sites via a High-Entropy Strategy for Accelerating Oxygen Electrode Reactions in Lithium-Oxygen Batteries.

High-entropy perovskite oxides, in which the B-type metal site of perovskite oxides (ABO3) is occupied by over five kinds of transition metal ions, show promising applications in energy storage and conversion fields. Herein, high-entropy perovskite oxides (LaSr(5TM)O3) composed of Cr, Mn, Fe, Co, and Ni at the B-type metal site are prepared as oxygen electrocatalysts for Li-O2 batteries. The presence of compressive strain in LaSr(5TM)O3 effectively regulates the 3d orbit occupancy of the active Co site (Co2+ → Co3+) and lifts the energy level of the Co d-band center, thus leading to enhanced adsorption toward the LiO2 intermediate on Co sites. Furthermore, the high electron-drawing capability of Cr sites ensures sufficient electron exchange and further strengthens the adsorption of LiO2. As expected, the Li-O2 battery with a LaSr(5TM)O3 electrode delivers a low overpotential (0.79 V) and superior cyclability (226 cycles). This study provides a meaningful strain strategy to improve the electrocatalytic activity of multicomponent oxides via fabricating high-entropy materials.

Enhanced resistance to electrochemical degradation and hydrogen permeation by grain boundary and strain engineering in cobalt-graphene oxide composite coatings

Cobalt (Co) and cobalt-graphene oxide (Co-GO) coatings were electrodeposited on mild steel. The Co-GO coating with an optimum volume fraction of GO (Co-GO-3) displayed significantly reduced corrosion current density (5.3 μA/cm2) compared to pristine cobalt coating (21.4 μA/cm2) in 3.5 wt% NaCl solution. Formation of a stable CoO passive oxide layer and a higher proportion of low energy grain boundaries (low-angle grain boundaries and CSL boundaries) contributed to the enhanced anti-corrosion properties. The Co-GO-3 coating also exhibited the lowest hydrogen permeation current, attributed to its higher fraction of relatively closed grain boundaries and presence of compressive strain within the coating.

Crystalline–amorphous Ni4.5Fe4.5S8/NiFeS heterostructure for alkaline water oxidation electrocatalysis

Electrochemical water splitting, hailed for its cost-effectiveness and eco-friendliness in hydrogen energy production, faces a significant impediment in the form of the oxygen evolution reaction (OER), characterized by inherently slow kinetics. Addressing this challenge, the utilization of crystalline-amorphous (c-a) heterostructures, offering precise interface modulation, emerges as a promising solution. In this study, we report the synthesis of a robust electrode comprising of crystalline Ni4.5Fe4.5S8 nanospheres integrated with amorphous NiFeS nanosheets (denoted as NiFeS-TH) using a hydrothermal approach. Remarkably, this electrode exhibits exceptional performance in alkaline electrolytes, requiring a mere overpotential of 420 mV to attain a current density of 2 A/cm2. This enhanced OER performance is attributed to the substantial electrochemically active surface area and the presence of compressive strain at the interfaces. These profound insights into heterostructure design hold the potential to revolutionize the tailoring and optimization of OER efficiency.

Low temperature magnetic and structural properties of Sr-doped La2CoMnO6 (La2-xSrxCoMnO6: 0 ≤ x ≤ 0.08) double perovskite nanoparticles

A study on crystal structure and physical properties has been performed on nanoparticles of lead-free double perovskites, La2CoMnO6 (LCMO) and Sr-doped La2-xSrxCoMnO6 (LSMO:0 ≤ x ≤ 0.08) prepared by the sol–gel synthesis method. In preparation for the LSMO nanoparticle, the La site of the LCMO double perovskite was replaced with an increasing concentration of Sr atom. Structural investigation done by employing the X-ray Diffraction technique indicates that the crystallite size decreases as the doping concentration increases. The Rietveld refinement on the XRD pattern shows the formation of the rhombohedral phase of LCMO (S.G. no. 161). Strain in the prepared samples estimated from Williamson Hall (W-H) analysis shows that the strain decreases as crystallite size decreases. The presence of compressive strain is also evident from the blue shift obtained in the Raman spectrum of the nanoparticles. The UV–Vis spectra reveal the maximum absorption in the near UV region of the electromagnetic spectrum. The Bandgap analysis from Tauc’s plot shows an increase in band gap with Sr doping in the LCMO host lattice (from 1.81 eV to 1.92 eV). This is attributed to the decrease in crystallite size and octahedral tilting with Sr doping. Resistivity versus temperature plots reveal the semiconducting nature of the compound. A linear nature graph between lnρ and T-14 indicates that the electric transport mechanism is governed by the variable range Hopping (VRH) model. The M−H curves show that the maximum magnetization decreases as a result of Sr doping due to the anti-site disorder introduced. dM/dT vs T curve shows two magnetic transitions at ∼ 215 K and at ∼ 173 K which are due to Co2+–O2--Mn4+ and Co3+–O2--Mn4+ ferromagnetic superexchange interactions, respectively.

Atomic strain and catalytic properties of formate oxidation and dehydrogenation in AgPd nanoalloys.

Formate is a promising hydrogen carrier for safe storage and transport and a fuel for direct formate fuel cells. However, the sluggish kinetics of catalysts for formate dehydrogenation (FDH) and oxidation reactions (FORs) significantly limit the potential applications of formate. Strain effects can effectively modulate catalytic properties by altering the electronic structure. Nevertheless, the lack of theoretical principles to quantify atomic strain and its effects on FDH and FOR catalytic activity has made experimental efforts laborious. In this work, we establish a database of atomic strain distributions for AgPd nanoalloys, reveals that the presence of compressive strain at the edges and corners and compressive strain exerted on the surface of Ag@Pd nanoalloys, particularly the one with an icosahedral shape, boost the FDH and FOR catalytic activity by shifting down the d-band center, thus weakening the adsorption of key intermediate Had. This study provides a theoretical perspective on the development and use of formate as a hydrogen carrier and fuel.

Influence of compressive strain on the hydrogen storage capabilities of graphene: a density functional theory study

Pristine graphene is not suitable for hydrogen storage at ambient conditions since it binds the hydrogen molecules only by van der Waals interactions. However, the adsorption energy of the hydrogen molecules can be improved by doping or decorating metal atoms on the graphene monolayer. The doping and decoration processes are challenging due to the oxygen interference in hydrogen adsorption and the clustering issue of metal atoms. To improve the hydrogen adsorption energy in pristine graphene, we have explored the hydrogen storage capabilities of graphene monolayer in the presence of compressive strain. We found that at 6 % of biaxial compressive strain, a 4*4*1 supercell of graphene can adsorb 10 H$_2$ molecules above the graphene surface. The average binding energy of H$_2$ for this configuration is found to be -0.42 eV/H$_2$, which is very suitable for reversible hydrogen adsorption. We propose that a 4*4*1 supercell of graphene can adsorb a total number of 20 H$_2$ molecules leading to a high hydrogen uptake of 9.4 %. The interaction between orbitals of carbon and hydrogen atoms and the charge transfer process have been studied by plotting the partial density of states and surface charge density plots. The electronic density around the C-C bonds of graphene increases in the presence of compressive strain, due to which hydrogen molecules are strongly adsorbed.

Tuning the electronic, phonon, and optical properties of monolayer BX (X[dbnd]P and As) through the strain effect

Strain engineering has widely been recognized as a highly sensitive and effective way to modulate the physical properties of materials. Here, we thoroughly investigate the effects of biaxial strain-driven optoelectronic properties and thermodynamic stability of BX (XP and As) monolayers under a density functional framework. The electronic bandgap at the K-point of these materials increases with tensile (0 to +10%) strain and decreases in the presence of compressive (−10% to 0) strain. The phonon modes indicate that monolayer BP becomes thermodynamically unstable with larger than 4% compressive strain, and BAs loses stability at 4% compressive strain. However, both structures can show quite stable nature for up to + 8% tensile strain. In the presence of compressive strain, the longitudinal optical (LO) and transverse optical (TO) phonon modes become softening in nature. In contrast, it displays hardening behavior with the tensile strain in these materials. Also, superior light absorption near the infrared and visible light spectrum is feasible by the BP and BAs monolayer when the biaxial strain is incorporated. These results elucidate a promising way to manipulate the optical and electronic properties of monolayer BP and BAs via strain engineering and eventually make these materials promising for futuristic spintronics, electronics, and optoelectronic device applications.

Catalytic reduction of carbon dioxide over two-dimensional boron monolayer

• This work studies the electrochemical reduction of CO 2 on boron nanosheets, metal-free catalyst, under the scheme of density functional theory (DFT) and microkinetic modeling. • The strain can turn metallic two-dimensional boron nanosheet to semiconductor, not only making boron sheets possess photo(electro)catalytic activity (1.4 eV), but also improving energy efficiency and selectivity performance against hydrogen evolution reaction. • Thermodynamic and microkinetic models are applied to demonstrate the favorable products, critical steps and hydrogenation mechanisms. • By introducing the aqueous electrolytes, the hydrated alkali cations not only effect on the CO 2 concentration, but also produce a bigger surface charge density and stronger interfacial electric filed. Carbon dioxide reduction (CRR) is an attractive strategy for alleviating global warming and producing valuable fuels. In this work, we study the catalytic conversion of CO 2 to C 1 -C 3 products on boron nanosheet in the presence of compressive strain by using density functional theory. Thermodynamic and microkinetic models are applied to demonstrate the favorable products, critical steps, and hydrogenation mechanisms. As demonstrated, the strain can turn metallic two-dimensional boron nanosheet to semiconductor, not only making boron sheets possess photo(electro)catalytic activity, but also improving energy efficiency and selectivity performance against hydrogen evolution reaction. By introducing the aqueous electrolytes, the hydrated alkali cations not only effect on the CO 2 concentration, but also produce a bigger surface charge density and stronger interfacial electric filed. Especially, the selectivity of C 2+ products is enhanced with the increase of alkali cations size by decreasing the kinetic barrier for CO dimerization and stabilizing the intermediates. The results highlight the significance of metal-free catalysts for CRR by the photoelectrochemical method and provide novel avenues for the development of new solar-energy utilization catalysts.

Drastic effect of impurity scattering on the electronic and superconducting properties of Cu-doped FeSe

Non-magnetic impurities in iron-based superconductors can provide an important tool to understand the pair symmetry and they can influence significantly the transport and the superconducting behaviour. Here, we present a study of the role of strong impurity potential in the Fe plane, induced by Cu substitution, on the electronic and superconducting properties of single crystals of FeSe. The addition of Cu quickly suppresses both the nematic and superconducting states, and increases the residual resistivity due to enhanced impurity scattering. Using magnetotransport data up to 35 T for a small amount of Cu impurity, we detect a significant reduction in the mobility of the charge carriers by a factor of ~3. While the electronic conduction is strongly disrupted by Cu substitution, we identify additional signatures of anisotropic scattering which manifest in linear resistivity at low temperatures and $H^{1.6}$ dependence of magnetoresistance. The suppression of superconductivity by Cu substitution is consistent with a sign-changing $s_{\pm}$ order parameter. Additionally, in the presence of compressive strain, the superconductivity is enhanced, similar to FeSe.

Antisolvent-assisted one-step solution synthesis of defect-less 1D MAPbI3 nanowire networks with improved charge transport dynamics

Abstract In this study, both one-dimensional (1D) and three-dimensional (3D) methylammonium lead iodide (MAPbI3) were successfully synthesized from the same starting precursor solution using a one-step in situ spin-coating process assisted by antisolvent washing with different ethereal solvents. Antisolvent washing with diethyl ether (DE) induced isotropic growth, resulting in dense 3D MAPbI3 films. However, washing with dibutyl ether (DB) having complementary properties promoted 1D directional growth to avoid steric hindrance in the DB/perovskite complex. Antisolvent DB having a lower vapor pressure than DE retarded the vaporization of dimethylformamide and facilitated the growth of larger grains with fewer defects through the slow crystallization. It was also found that long-chain induced 1D directional growth creates an internal compressive strain in the 1D NW film, which plays an important role in charge carrier dynamics. To compare the power conversion efficiency (PCE) and charge transport dynamics, planar solar cells based on both 1D and 3D perovskites were fabricated. 1D NW perovskite based devices achieved a longer lifetime and faster carrier transport owing to the limited ion migration in the presence of compressive strain, although the PCE (15.73%) of the 1D NW-based device was lower than that (18.73%) of the 3D bulk-based device due to inevitable pore incorporation. The improved charge carrier dynamics of 1D NW MAPbI3 can offer potential advantages in the development of optoelectronic devices.

Effects of strain and electric fields on the electronic transport properties of single-layer β12-borophene nanoribbons.

Motivated by recent experimental and theoretical research on a monolayer of boron atoms, borophene, the transmission probability and current-voltage characteristics of β12-borophene nanoribbons (BNRs) with zigzag and armchair edges have been calculated using the five-band tight-binding calculation, the Green's function approach, and the Landauer-Büttiker formalism. We focus on the effects of the geometrical parameters, perpendicular electric field, and external strain on the electronic transport properties of β12-BNRs by considering the effects of the substrate. Our calculations show that the transmission coefficient and current of the system decrease by increasing the channel length, whereas increasing ribbon width leads to an increment in the transmission probability as well as the I-V characteristic of β12-BNRs. Besides, the application of tensile strain causes a decrement in the current of the inversion symmetric model of the armchair β12-BNR, whereas the current increases in the presence of compressive strain. We also observed a dip in the transmission spectrum of the biased β12-BNR along the armchair direction which shows a metal-to-n-doped semiconductor phase transition in the device when applying a strong enough electric field. Moreover, the current of the inversion symmetric model of the β12-BNR with zigzag and armchair edges increases with the application of a perpendicular electric field, while in the case of the homogeneous model, the application of an electric field enhances the current of the β12-BNR only in the zigzag direction. These results provide insights for future experimental research and show that β12-BNRs are potential candidates for next-generation electronic devices.

Effect of CNT on the growth and agglomeration of TiO2 nanoparticles

Titanium dioxide nanoparticles (TiO2 -NPs) are agglomerated by inclusion of CNTs during the nucleation and growth process using the hydrothermal method at 160 ⁰C. The content of C-atoms was determined from EDAX-spectra and line scan. The XRD peak of TiO2 indicated the rutile phase R(210), while CNT- TiO2 showed the anatase phase A(004). Williamson-Hall (W-H) models showed the linear fitted negative slope, indicated the presence of compressive strain in TiO2 and CNT- TiO2 crystal lattice. Agglomeration of TiO2 nanoparticles was confirmed from the surface morphology and elemental analysis. The FTIR spectra showed the interfacial interaction between CNTs and TiO2 with vibrational frequency of Ti-O-C bonds at 1065 cm-1

Inorganic gas sensing of green phosphorene nanosheet: insights from density functional theory

Our work highlights the functionality of a novel two-dimensional phosphorene allotrope entitled green phosphorene for inorganic gas detection for the first time. Four inorganic molecules, NH3, SO2, HCN and O3, are considered as adsorbates and the adsorption conformation, adsorption energy, charge transfer, density of states, and electronic band structure are systematically scrutinized based on density functional theory. Our calculations show that the adsorption energy of O3 on pristine green phosphorene is the lowest among the four considered gas molecules, suggesting that the substrate is more sensitive to O3. Significant changes in electronic structures confirm the possibility of green phosphorene for O3 detection. Biaxial strains and electric fields were applied to investigate the changes in adsorption behavior. The presence of compressive strain could enhance adsorption sensitivity between O3 and green phosphorene, while the tensile strain induces the dissociative adsorption that not suitable for reversible sensor. Furthermore, by controlling the orientation of external electric field, it is possible to achieve O3 adsorption-desorption cycle, which is of great significance for green phosphorene in the application of reversible gas sensor.

Structural stability and optoelectronic properties of tetragonal MAPbI3 under strain

In recent years, organic–inorganic hybrid perovskites have attracted wide attention due to their excellent optoelectronic properties in the application of optoelectronic devices. In the manufacturing process of perovskite solar cells, perovskite films inevitably have residual stress caused by non-stoichiometry components and the external load. However, their effects on the structural stability and photovoltaic performance of perovskite solar cells are still not clear. In this work, we investigated the effects of external strain on the structural stability and optoelectronic properties of tetragonal MAPbI3 by using the first-principles calculations. We found that the migration barrier of I− ion increases in the presence of compressive strain and decreases with tensile strain, indicating that the compressive strain can enhance the structural stability of halide perovskites. In addition, the light absorption and electronic properties of MAPbI3 under compressive strain are also improved. The variations of the band gap under triaxial and biaxial strains are consistent within a certain range of strain, resulting from the fact that the band edge positions are mainly influenced by the Pb–I bond in the equatorial plane. Our results provide useful guidance for realizing the commercial applications of MAPbI3-based perovskite solar cells.

Compressive Strain in Core-Shell Au-Pd Nanoparticles Introduced by Lateral Confinement of Deformation Twinnings to Enhance the Oxidation Reduction Reaction Performance.

In this work, quasi-spherical, uniform gold nanoparticles with rich deformation twinning (Audt NPs) were first synthesized with the assistance of copper(II) ions. Then, these Audt NPs were used as the cores for the fabrication of core-shell (CS) Audt-Pd NPs with ultrathin Pd layers, which also can bear compressive strain because of the formation of corrugated structured Pd shells led by the lateral confinement imposed by deformation twinning in the Au cores. The presence of compressive strain in the CS Audt-Pd NPs can result in the widening of the d-band width of the Pd shell and further the downshift of their d-band center, which can then improve the desorption ability of intermediates and still maintain the adsorption ability of the reactants because of the broad adsorption potential range. Taking the oxidation reduction reaction and the ethanol oxidation reaction as examples, the as-prepared Audt-Pd NPs indeed exhibited superior catalytic performances because of the synergism of compressive strain and the electronic effect. Thus, our work opens a new way to introduce compressive strain in the Pd-based CS NP catalysts, which can achieve the enhancement in the electrocatalytic performance by combining the merit of compressive strain and the electronic effect.

Influence of nitrogen dopant source on the structural, photoluminescence and electrical properties of ZnO thin films deposited by pulsed spray pyrolysis

The N-doped ZnO thin films have been deposited using pulsed spray pyrolysis from Zinc Acetate (ZA) precursor along with the N dopants of N2 carrier gas (N2 – series) and Ammonium Acetate (AA – series) on glass substrates at the optimized substrate temperature of 300 °C with different spraying pulse intervals. The X-ray powder diffraction studies confirmed the polycrystalline structures with the presence of mixed compressive and tensile strain along ‘a’ and ‘c-axes’ respectively for the N2 doped films and the presence of compressive strain alone along both ‘a’ and ‘c-axes’ for the AA doped films. The XPS analysis revealed that the N2 gas source led to the incorporation of elemental N into the film and the AA source led to the incorporation of both elemental and molecular N into the film. The Micro Raman Analysis confirmed the N-doping and its contributed carrier localization by exhibiting A1(LO) and A1(TO) modes. Photoluminescence studies exhibited the active band gap of ~3.19 eV with additional peaks related to hole traps at ~3 eV and electron traps at ~2.8 eV without exhibiting peaks correspond to oxygen vacancy defects. The Seebeck measurements confirmed the establishment of intrinsic p-type conductivity in both the cases at room temperature (RT) and the films deposited with pure elemental doping from N2 source found exhibiting better p-type conductivity than those films deposited using AA source.

Modification of the optoelectronic properties of reactively evaporated In6Se7 thin films by Sn doping for photovoltaic applications

Sn doped In6Se7 thin films with 5 wt% and 10 wt% Sn are prepared on glass substrate using reactive evaporation technique. The samples are characterized by XRD, FESEM, XPS and UV–Vis–NIR Spectrophotometer. XRD result shows that the samples are polycrystalline with monoclinic structure. Presence of compressive strain and lattice space shrinkage is observed in 10 wt% Sn doped sample. A detailed study of the optical properties demonstrated that a blue shift of 0.02 eV in the optical band gap of 5 wt% Sn doped sample is due to Burstein–Moss effect. Band gap narrowing in 10 wt% Sn doped sample is explained in terms of defect induced static disorder. 5 wt% Sn doped sample exhibits lowest resistivity and improved photoconductivity compared to undoped sample. This enhancement in optoelectronic properties facilitates the use of such films in photovoltaic applications.

First-principles studies on the superconductivity of aluminene

Group III mono-elemental two-dimensional (2D) materials have been an active area of research since the experimental demonstration of monolayer boron. Using first-principles calculations, we predict a new type of buckled monolayer aluminum (aluminene) which exhibits metallic characteristics. From the phonon dispersion and cohesive energy calculations, the free-standing aluminene is structurally stable. The stability of the aluminene is maintained under tensile strain up to 7%. In contrast, the stability of the structure is not preserved in the presence of compressive strain. We also carried out a systematic analysis on the electron–phonon coupling in the aluminene structure and found that aluminene in its pristine form can superconduct with superconductivity critical temperature, Tc of 6.5 K. The Tc is further enhanced to 11.9 K with the presence of 7% bi-axial tensile strain. Our calculations show that the higher Tc is because of stronger electron–phonon coupling resulted from the increase of density of states at Fermi level with tensile strain.

High In-content InGaN layers synthesized by plasma-assisted molecular-beam epitaxy: Growth conditions, strain relaxation, and In incorporation kinetics

We report the interplay between In incorporation and strain relaxation kinetics in high-In-content InxGa1-xN (x = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x = 0.13–0.48, best structural and morphological qualities are obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analyses of the evolution of the crystalline structure with the layer thickness point to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm, which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e., indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface.

Synthesis, structural and magnetic characterization of lead-metaniobate/cobalt-ferrite nanocomposite films deposited by pulsed laser ablation

Detailed structural, microstructural and magnetic measurements were performed on (PbNb2O6)1−x –(CoFe2O4) x nanocomposite thin films deposited by laser ablation on Si(001)\Pt substrates, with different cobalt ferrite concentrations. The tuning of the lead concentration, due to the lead volatility, was found to be particularly important in order to obtain the orthorhombic (ferroelectric) lead niobate phase. The lattice parameter of CoFe2O4 was below the bulk value, indicating the presence of compressive strains on this phase. A magnetic anisotropy was observed, which favored the orientation of the magnetization in the direction perpendicular to the plane of the films, for cobalt ferrite concentrations 40–50 %. The shape, stress and magnetocrystalline anisotropy fields on the composites were calculated and compared. It was found that the perpendicular magnetic anisotropy was induced by the presence of strain on the ferrite phase in the films.