Lattice Compression Research Articles

Charge-Induced Lattice Compression in Monolayer MoS2

Electron beam or photonic excitation of localized surface plasmon resonances (LSPRs) in gold nanoparticles and their subsequent nonradiative relaxation create a nonuniform charge distribution near the metal–semiconductor interface via hot-electron injection from gold nanoparticles to the monolayer MoS2 conduction band states. These charge domains induce lattice compression in the MoS2 lattice because of the inverse piezoelectric response arising due to the noncentrosymmetric nature of the crystal lattice. Our high-resolution transmission electron microscopy studies reveal that as much as 9–10% biaxial compressive strain is generated in free-standing monolayer MoS2 in the vicinity of gold nanoparticles, which relaxes rapidly within 50 nm from the edge of the gold nanoparticle. The metal interface-induced hot-electron injection via photonic excitation of LSPRs and the resultant lattice distortion also manifest in shifts as well as broadening of A1g(Γ) and E2g1(Γ) Raman modes of the monolayer MoS2 in presenc...

Crystallographic orientation dependence of mechanical properties in the superelastic Ti-24Nb-4Zr-8Sn alloy

Nanoindentation and electron backscattered diffraction techniques are used to study the dependence of crystallographic orientation on mechanical properties in individual grains of the superelastic polycrystalline Ti-24Nb-4Zr-8Sn alloy. Strain recovery, elastic modulus, and hardness are evaluated from the force-displacement curves using spherical and Berkovich indenters. Experimental data are reported in a standard stereographic triangle covering all possible crystallographic directions of loading in the bcc-\ensuremath{\beta} structure of the Ti-24Nb-4Zr-8Sn alloy. Our experiments show that both spherical and Berkovich indenters are suitable for probing anisotropy of elastic modulus whereas spherical indenter is more appropriate for probing anisotropy of superelastic response. The highest indentation strain recovery is measured along $\ensuremath{\langle}001{\ensuremath{\rangle}}_{\ensuremath{\beta}}$ and the lowest one is observed along $\ensuremath{\langle}111{\ensuremath{\rangle}}_{\ensuremath{\beta}}$. Our inverse pole figure distribution of indentation strain recoveries is in good agreement with inverse pole figure distribution of compressive lattice distorsions calculated from the crystallographic model of martensitic transformation in \ensuremath{\beta} titanium alloys. This established pattern in compression is very different from that seen during tensile deformation, and both our experiments and calculations confirm the strong tension-compression asymmetry of the strain response in superelastic \ensuremath{\beta} titanium alloys. The indentation modulus also shows significant crystallographic anisotropy: ${E}_{[001]\ensuremath{\beta}}<{E}_{[101]\ensuremath{\beta}}<{E}_{[111]\ensuremath{\beta}}$. In contrast, orientation dependence is lost when plasticity has set in, and hardness becomes independent of crystallographic orientation due to the fact that multiple directions are prone to generate slip systems in the bcc-\ensuremath{\beta} structure.

One-Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super-ionic Phase Attributes.

Cuprous selenide nanocrystals have hallmark attributes, especially tunable localized surface plasmon resonances (LSPRs) and super-ionic behavior. These attributes of cuprous selenide are now integrated with a one-dimensional morphology. Essentially, Cu2 Se nanowires (NWs) of micrometer-scale lengths and about 10 nm diameter are prepared. The NWs exhibit a super-ionic phase that is stable at temperatures lower than in the bulk, owing to compressive lattice strain along the radial dimension of the NWs. The NWs can be switched between oxidized and reduced forms, which have contrasting phase transition and LSPR characteristics. This work thus makes available switchable, one-dimensional waveguides and ion-conducting channels.

One‐Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super‐ionic Phase Attributes

AbstractCuprous selenide nanocrystals have hallmark attributes, especially tunable localized surface plasmon resonances (LSPRs) and super‐ionic behavior. These attributes of cuprous selenide are now integrated with a one‐dimensional morphology. Essentially, Cu2Se nanowires (NWs) of micrometer‐scale lengths and about 10 nm diameter are prepared. The NWs exhibit a super‐ionic phase that is stable at temperatures lower than in the bulk, owing to compressive lattice strain along the radial dimension of the NWs. The NWs can be switched between oxidized and reduced forms, which have contrasting phase transition and LSPR characteristics. This work thus makes available switchable, one‐dimensional waveguides and ion‐conducting channels.

Putting the Squeeze on Lead Iodide Perovskites: Pressure-Induced Effects To Tune Their Structural and Optoelectronic Behavior.

Lattice compression through hydrostatic pressure has emerged as an effective means of tuning the structural and optoelectronic properties of hybrid halide perovskites. In addition to external pressure, the local strain present in solution-processed thin films also causes significant heterogeneity in their photophysical properties. However, an atomistic understanding of structural changes of hybrid perovskites under pressure and their effects on the electronic landscape is required. Here, we use high level ab initio simulation techniques to explore the effect of lattice compression on the formamidinium (FA) lead iodide compound, FA1–xCsxPbI3 (x = 0, 0.25). We show that, in response to applied pressure, the Pb–I bonds shorten, the PbI6 octahedra tilt anisotropically, and the rotational dynamics of the FA+ molecular cation are partially suppressed. Because of these structural distortions, the compressed perovskites exhibit band gaps that are narrower (red-shifted) and indirect with spin-split band edges. Furthermore, the shallow defect levels of intrinsic iodide defects transform to deep-level states with lattice compression. This work highlights the use of hydrostatic pressure as a powerful tool for systematically modifying the photovoltaic performance of halide perovskites.

Pressure-enhanced interplay between lattice, spin, and charge in the mixed perovskite La2FeMnO6

Spin crossover plays a central role in the structural instability, net magnetic moment modification, metallization, and even in superconductivity in corresponding materials. Most reports on the pressure-induced spin crossover with a large volume collapse so far focused on compounds with single transition metal. Here we report a comprehensive high-pressure investigation of a mixed Fe-Mn perovskite La2FeMnO6. Under pressure, the strong coupling between Fe and Mn leads to a combined valence/spin transition: Fe3+(S = 5/2) to Fe2+(S = 0) and Mn3+(S = 2) to Mn4+(S = 3/2), with an isostructural phase transition. The spin transitions of both Fe and Mn are offset by ~ 20 GPa of the onset pressure, and the lattice collapse occurs in between. Interestingly, Fe3+ ion shows an abnormal behavior when it reaches a lower valence state (Fe2+) accompanied by a + 0.5 eV energy shift in Fe K-absorption edge at 15 GPa. This process is associated with the charge-spin-orbital state transition from high spin Fe3+ to low spin Fe2+, caused by the significantly enhanced t2g-eg crystal field splitting in the compressed lattice under high pressure. Density Functional Theory calculations confirm the energy preference of the high-pressure state with charge redistribution accompanied by spin state transition of Fe ions. Moreover, La2FeMnO6 maintains semiconductor behaviors even when the pressure reached 144.5 GPa as evidenced by the electrical transport measurements, despite the huge resistivity decreasing 7 orders of magnitude compared with that at ambient pressure. The investigation carried out here demonstrates high flexibility of double perovskites and their good potentials for optimizing the functionality of these materials.

Structural and magnetic properties of YCo4B compound at high pressures

The crystal structure and magnetic properties of YCo4B intermetallic compound were studied by means of neutron diffraction at pressures p ≤ 6.5 GPa. No structural transitions are evidenced. The cobalt moments at 2c and 6i sites decrease, upon lattice compression, with a rate dlnMCo/dp ≅ 0.11 GPa−1, showing a rather high degree of itinerancy. The evolutions with pressure of band structures have been also analysed and the computed cobalt moments are discussed in correlation with those experimentally determined.

Double dependence of H diffusion in tungsten from first-principles determination: strain and temperature

The hydrogen (H) diffusion in tungsten (W) is an important factor for the use of W as the plasma facing material in a fusion reactor. However, under the environment of fusion, high energy neutron irradiated-W unavoidably leads to the possible local strain so as to cause the lattice expansion or compression, which changes the diffusion behaviors of H in W. In view of this, we have carried out first-principles calculations to determine the interstitial H migration properties under double effects of isotropic strain and temperature in W. For both strain-free and strain-applied (including tension and compression) cases, the H migration energy raises when the temperature rises from 300 to 1800 K. While at each fixed temperature T = 300, ..., 1800 K, the H migration energy can reduce/increase significantly with the increasing tensile/compressive strain. The vibration free energy contribution plays a key role in the H migration energy with the temperature at both strain-free and strain-applied W systems.

Effective surface termination with Au on PtCo@Pt core-shell nanoparticle: Microstructural investigations and oxygen reduction reaction properties

We investigated the microstructures of Au-deposited PtCo@Pt core-shell nanoparticles (NPs) and discussed enhancement of the oxygen reduction reaction (ORR) properties by Au termination of low-coordination sites of the Pt-shell. The Au-deposited PtCo@Pt NPs showed an improved electrochemical structural stability, together with slight increment in increased initial, pristine area-specific activity relative to the non-Au-deposited PtCo@Pt NPs. Atomic-level microstructural characterization was performed by a back-side illumination fluorescence X-ray absorption fine structure (BI-FXAFS) method and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS). The BI-FXAFS results indicated that compressive lattice strain in the Pt-shells of the PtCo@Pt NPs was almost unchanged by the subsequent Au deposition. Furthermore, STEM-EDS mapping of Pt, Co, and Au clearly showed that the deposited Au tended to localize at low-coordination sites of the Pt-shell surface, e.g., edges and corners. The atomic-level microstructural characterization conducted in this study demonstrated that effective Au surface terminations of the Pt-shell enhance the ORR durability of Pt-based core-shell type NP catalysts.

In-situ electron microscopy mapping of an order-disorder transition in a superionic conductor

Solid-solid phase transitions are processes ripe for the discovery of correlated atomic motion in crystals. Here, we monitor an order-disorder transition in real-time in nanoparticles of the super-ionic solid, Cu2−xSe. The use of in-situ high-resolution transmission electron microscopy allows the spatiotemporal evolution of the phase transition within a single nanoparticle to be monitored at the atomic level. The high spatial resolution reveals that cation disorder is nucleated at low co-ordination, high energy sites of the nanoparticle where cationic vacancy layers intersect with surface facets. Time-dependent evolution of the reciprocal lattice of individual nanoparticles shows that the initiation of cation disorder is accompanied by a ~3% compression of the anionic lattice, establishing a correlation between these two structural features of the lattice. The spatiotemporal insights gained here advance understanding of order-disorder transitions, ionic structure and transport, and the role of nanoparticle surfaces in phase transitions.

Effect of degree of strain relaxation on polarization charges of GaN/InGaN/GaN hexagonal and triangular nanowire solar cells

The innovative contribution of this paper is to derive polarization charges in hexagonal and triangular GaN/InGaN/GaN core/shell/shell nanowire solar cells considering effect of degree of strain relaxation (R) and appropriate stiffness coefficients. The crystal orientation angle, φ and non-linear effect of spontaneous polarization are tailored with strain calculations for a better precision of polarization charges in nanowire type devices. The article also formulated the effect of polarization charges while InGaN layers are grown above or below GaN layer in both types of nanowires depending on the lattice expansion or compression. The model accounts an innovative concept of polarization charges distribution with respect to growth of crystal orientation and strain relaxation. It is observed that nanowire solar cell with triangular geometry could be good enough for efficient generation of power as compared to hexagonal nanowire solar cell. This concept of one triangular nanowire solar cell exhibits an efficiency of 3.18% with 90.34% fill factor under 1 Sun AM1.5 illumination with 20% ‘In’ composition.

Anharmonicity in elastic constants and extended x-ray-absorption fine structure cumulants

We have investigated temperature dependence of the elastic constants and higher-order EXAFS (extended x-ray-absorption fine structure) cumulant moments, both of which originate from vibrational anharmonicity. We focus our attention on how the third- or fourth-order anharmonicity contributes to these physical quantities. Although it may be believed that the fourth-order anharmonicity should dominantly contribute to the fourth-order EXAFS cumulant through the first-order quantum statistical perturbation theory, it is consequently found that the experimental fourth-order EXAFS cumulant observed in fcc Ni, Cu, and stainless steel 316 are described mainly by the third-order anharmonicity through the second-order perturbation. In case of the elastic constants, such a situation is more prominent, and the contribution of the fourth-order anharmonicity is negligibly small for the estimation of temperature dependence of the elastic constants. We have also observed significant lattice strains on Cr and Mo in stainless steel 316 through the Fe, Ni, Cr, and Mo K-edge EXAFS measurements: a compressive lattice strain on Cr associated with larger thermal fluctuations and a more significant compressive lattice strain on Mo without enhanced thermal fluctuation. Such a characteristic dissimilarity may be caused by the differences in the atomic weights and the cohesive energies between Cr and Mo. Moreover, we have performed path-integral effective classical potential and classical Monte-Carlo simulations to describe the bulk moduli of the Invar and Elinvar alloys that show noticeable anomalies due to the so-called Invar effect. Appropriate temperature dependence of the bulk moduli is successfully obtained for the Invar, Elinvar, and stainless steel 304 and 316 alloys as well as elemental fcc Cu and Ni metals.

Дефектонный вклад в высокотемпературную сверхпроводимость гидридов

The high pressure of the order of hundreds of gigapascals required to obtain the high-temperature superconducting phases of a number of hydrides causes the crystal lattice compression, which in turn leads to an exponential increase in the probability of a hydrogen atom tunneling between equivalent interstices. At low temperatures, vacancies in the filled under stoichiometry hydrogen sublattice and hydrogen atoms in the completely free under stoichiometry interstice sublattice are quantum defect - defectons. The estimate of the defecton contribution into the superconductivity of hydrides has been obtained and has been shown that it can be substantial either in the case of free defectons, or in the case of defectons, clusterized with the formation of two-level systems.

Piezoelectric properties of a near strain-free lead zirconate titanate thin films deposited on a Si substrate

Chemical solution deposition (CSD)-derived near strain-free lead zirconate titanate (PZT) thin films on a Si substrate were prepared by designing a buffer layer structure. Strain-free PZT thin films with different compositions ranging from Zr/Ti = 50/50 to 58/42 were obtained to demonstrate lattice strain effects on piezoelectric properties. Results show that a near strain-free condition was attained with a SrRuO3 (SRO: 160 nm)/(La0.5,Sr0.5)CoO3 (LSCO: 90 nm)/LaNiO3 (LNO: 120 nm)/stacking structure, even on a Si substrate. The highest effective d33 value of the near strain-free PZT thin film was observed at 53/47 composition, which is the same as bulk materials, although the highest effective d33 value was obtained from 58/42 composition under the compressive lattice strain condition.

Three Topological Isomers of 1D- and 2D-Coordination Polymers Consisting of Tricopper Pyrazolate SBUs and 4,4′-Trimethylenedipyridine Linkers: Effect of Pressure on the Structure

Three topologically isomeric coordination polymers of formula [CuII3(μ3-OH)(μ-Cl)(μ-pz)3Cl(tmpy)]n, consisting of triangular CuII–pyrazolate structural building units and flexible 4,4′-trimethylenedipyridine linkers, have been prepared and structurally characterized as 1D- and 2D-coordination polymers. Powder X-ray diffraction (PXRD) patterns under variable pressure (ambient, 8 GPa) reveal a reversible compression of the lattice up to ∼4 GPa, followed by the loss of crystallinity at higher pressure. Single-crystal X-ray diffraction data, collected using synchrotron radiation under pressure of 1 GPa, corroborate the PXRD, showing a lattice compression forcing the C–C–C angles of the trimethylene moiety of the linkers to become more obtuse.

A correlation between crystal structure and magnetic properties in co-doped BiFeO3 ceramics

Compositional and temperature evolution of crystal structure and magnetic properties of the BiFeO3-based compounds co-doped with Ca and transition metal ions - Mn, Ti or Nb was studied with X-ray diffraction and vibrating sample magnetometer techniques. It has been shown that the chemical substitution allows to vary structural parameters, thus modifying magnetic state of the parent cycloidal antiferromagnet. Regardless the type of transition elements, the changes in chemical composition result in a lattice compression, reduce rhombohedral distortions and stabilize a non-polar orthorhombic structure specific to the paraelectric state of BiFeO3. In all the systems, the co-doping gives rise to the disruption of the spatially modulated antiferromagnetic structure, thus providing the formation of a non-collinear antiferromagnetic order. In the Ca|Ti and Ca|Nb series, the chemical substitution leads to the stabilization of the weak ferromagnetic polar state with remnant magnetization up to 0.25 emu/g. Magnetic properties of the compounds co-doped with Ca and Mn ions are characterized by maximal remnant magnetization of about 0.07 emu/g. The factors driving the structural evolution and modification of magnetic behavior are discussed.

Boosting Tunable Syngas Formation via Electrochemical CO2 Reduction on Cu/In2O3 Core/Shell Nanoparticles.

In this work, monodisperse core/shell Cu/In2O3 nanoparticles (NPs) were developed to boost efficient and tunable syngas formation via electrochemical CO2 reduction for the first time. The efficiency and composition of syngas production on the developed carbon-supported Cu/In2O3 catalysts are highly dependent on the In2O3 shell thickness (0.4-1.5 nm). As a result, a wide H2/CO ratio (4/1 to 0.4/1) was achieved on the Cu/In2O3 catalysts by controlling the shell thickness and the applied potential (from -0.4 to -0.9 V vs reversible hydrogen electrode), with Faraday efficiency of syngas formation larger than 90%. Specifically, the best-performing Cu/In2O3 catalyst demonstrates remarkably large current densities under low overpotentials (4.6 and 12.7 mA/cm2 at -0.6 and -0.9 V, respectively), which are competitive with most of the reported systems for syngas formation. Mechanistic discussion implicates that the synergistic effect between lattice compression and Cu doping in the In2O3 shell may enhance the binding of *COOH on the Cu/In2O3 NP surface, leading to the enhanced CO generation relative to Cu and In2O3 catalysts. This report demonstrates a new strategy to realize efficient and tunable syngas formation via rationally designed core/shell catalyst configuration.

Magnetic field control of polarization/capacitance/voltage/resistance through lattice strain in BaTiO3-CoFe2O4 multiferroic nanocomposite

Magnetoelectric (ME) nanocomposites is a topic of intensive research due to their superficial potential in spintronic applications. In the present work, the magnetic field controlled electrical polarization is studied in hydrothermally synthesized multiferroic 0.25BaTiO3-0.75CoFe2O4 (BTO-CFO) nanocomposite. This multiferroic heterostructure is combined ferrimagnetic (CFO) with ferroelectric/piezoelectric (BTO) and achieved strain-mediated ME effect, which can effectively mediate magnetic anisotropy. The X-ray diffraction pattern confirmed polycrystalline phases of spinel CFO and tetragonal BTO, for which the compressive lattice strain is made. The microstructural study has evaluated BTO-CFO nanoparticles formation and the value of d-lattice spacing is calculated. The room temperature magnetic hysteresis is arising which depends on CFO inversion degree, and the change in bond-angle/length along A and B-sites. The ferroelectric hysteresis is measured at room temperature, which changed with applied magnetic field, i.e., the phenomenon of reduction in domain wall pinning related with oxygen vacancies and grain boundaries effect. The magnetic field is also influenced impedance spectra to induce magnetoimpedance effect and the positive value of magnetoresistance is obtained. A giant magnetodielectric coefficient up to −27% is obtained at 1 kOe of field. A strain mediated ME coupling enhancement is obtained.

Structure and electrical properties of zinc oxide base iron doped ceramics

The search for new economically advantageous technologies of new zinc oxide based composite ceramic materials and the study of their structure and properties attract special attention today. These ceramics have a number of advantages as compared with materials prepared by more expensive technologies, due to the possibility to fabricate items having different shapes and sizes and particularly to vary their morphology, structure and phase composition. This allows controlling their functional properties by varying the powder particle size in charge, the temperatures, durations and atmospheres of synthesis and heat treatment, and the types of doping impurities in the ceramics. The structure and electrical properties of (FexOy)10(ZnO)90 ceramics (0 ≤ x ≤ 3; 1 ≤ y ≤ 4) synthesized in air using single- and two-stage synthesis methods have been studied. FeO, α-Fe2O3 and Fe3O4 powders or (α-Fe2O3 + FeO) mixture have been used for ZnO doping. X-ray diffraction, gamma-ray resonance spectroscopy and Raman spectroscopy data suggest that at average iron concentrations of 1–3 at.% the ceramic specimens contain at least three phases: the Zn1-δFeδO solid solution with a wurtzite structure, the ZnFe2O4 ferrite phase with a spinel structure and FexOy residual iron oxides which were used as doping impurities. Scanning electron microscopy and energy dispersion X-ray analysis have shown that the wurtzite phase grain size in the ceramic specimens decreases from several decades of microns for single-stage synthesis to submicron sizes for two- stage synthesis. We show that iron addition to ZnO induces a compression of the wurtzite phase crystal lattice, the compression of lattice magnitude being proportional to the oxygen content in the FexOy iron oxide doping agent. The temperature dependences of the electrical resistivity suggest that deep donor centers with an activation energy of about 0.37 eV are formed in the Zn1-δFeδO wurtzite phase. The temperature dependences of the electrical resistivity of electrons for undoped ZnO in the 6–300 K range and for doped (FeO)10(ZnO)90 ceramic synthesized in one stage exhibit a variable activation energy below 50 K which indicates a heavily disordered structure.

ZnO and carbon nanocomposites for enhanced photoelectrochemical sensing activity: influence of the carbon content

In this work, carbon and zinc oxide (ZnO:C) nanocomposites were obtained by a hydrothermal reaction process. ZnO nanoparticles were first prepared by a homogeneous coprecipitation method. Nanocomposites with atomic concentrations of carbon ranging from 39.4 to 69.7 wt.% were then attained. The microstructure and morphology of each prepared nanocomposite was investigated by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The ZnO:C nanocomposites were found to present a wurtzite-type hexagonal crystalline structure that shifted towards an amorphous state with increasing C content. Results showed that incorporating the covalent carbon at O sites in the ZnO lattice causes lattice compression. Due to their low band-gap energies, the photoresponses of the ZnO:C nanocomposites extended into the visible region. The sensing characteristics of ZnO:C nanocomposite films were also investigated, and a major improvement in the photoelectrochemical (PEC) efficiency was obtained when the C content was 39 wt.%.