Effect Of Domain Boundaries Research Articles

Decay of Taylor–Green flow type initial conditions in a two-dimensional domain

Geophysical flows are often two-dimensional (2D) in nature. The decay dynamics of the canonical, symmetric initial conditions defined by the Taylor–Green (TG) flow is simulated in a 2D domain. The standard lattice Boltzmann equation method with the Bhatnagar–Gross–Krook collision model is employed. The vortex dynamics is investigated for bounded and unbounded flows with various sets of Gaussian vortices and varying Reynolds numbers. The formation of thin filaments and the generation of small-scale structures near the no-slip walls are found. To characterize the decay properties, the integral quantities, namely, kinetic energy, E(t), enstrophy, Ω(t) , and palinstrophy, P(t), are tracked as a function of the eddy-turnover-time. The initial vortex population in the domain dictates the decay rate of these integral quantities. The energy spectra, E(k), are computed to investigate the effect of domain boundaries and vortex populations on energy distribution among different length scales for Re=50000 . The evolution of TG flow in a bounded domain shows an exponent close to −3, which may be attributed to the generation of thin filaments and small-scale structures in vortex-wall interactions. Exponent changes with an increase in the vortex populations.

Ordered deficient perovskite La2/3TiO3 films grown via molecular beam epitaxy

As the parent compound of a promising solid electrolyte material Li3xLa2/3−xTiO3, the perovskite La2/3TiO3 has potential for advancing research on Li-intercalated ionic conductors. Epitaxial La2/3TiO3 films have been grown by molecular beam epitaxy using a growth process consisting of deposition and annealing cycles, with in situ monitoring by electron diffraction. X-ray absorption spectroscopy confirms the tetravalent state of Ti in La2/3TiO3, and the as-grown films are insulating. X-ray diffraction reveals the presence of half-order peaks, indicating a doubling of the pseudocubic perovskite unit cell due to the ordering of La vacancies in alternating A-site layers. These results demonstrate that single-phase, vacancy-ordered epitaxial films of La2/3TiO3 can be stabilized with excellent crystalline and electronic properties over wafer-sized areas, making possible Li-ion intercalation studies in films with well-defined domain boundary properties. Such boundaries are known to profoundly influence Li-ion conduction within the material. Understanding the effects of domain boundaries on Li-ion conduction could lead to improvements in solid-state battery technology and pave the way for the development of more efficient and safer energy storage devices.

Effect of TiO2 addition on the structural and electrical properties of La0.67Ca0.33MnO3

Numerous studies have been conducted on perovskite manganites to enhance the low field magnetoresistance (LFMR). One effective approach is adding an insulating oxide as the artificial boundary layer outside the manganite grain. This research aims to determine the structural and electrical properties of La0.67Ca0.33MnO3 (LCMO) when added with different contents of TiO2. LCMO powder was prepared via sol–gel route before appended with TiO2 nanoparticle to form (1 − x) LCMO: x TiO2, x = 0.00, 0.005, 0.010, 0.030 and 0.050. The structural analysis by X-ray diffraction (XRD) revealed no significant changes in the lattice parameter, crystallite size, bond length and angle as the concentration of TiO2 increased. The TiO2 in LCMO caused an increase in resistivity and a decrease in metal–insulator transition (TMI). This indicates the double exchange (DE) has been suppressed by the TiO2 addition, which acts as disordered layers at LCMO grains surface. The electrical resistivity of the samples was fitted with theoretical models, and the conduction mechanism is explained by the grain/domain boundary effect and the small polaron hopping (SPH) model. The first fitting inferred that the grain/ domain boundary effect plays an inevitable role throughout the conduction in the metallic region. The latter supports the notion that the presence of TiO2 in the LCMO compound produces a more resistive grain boundary.

Elevational range size patterns of vascular plants in the Himalaya contradict Rapoport's rule

Abstract Elevational range size patterns reflect ecological and evolutionary processes, but they are also affected by geometric constraints. The confounding effect of these constraints led to an ongoing controversy about the elevational Rapoport's rule, which postulates a positive association between the range size and elevation, and about the plausibility of the climate variability hypotheses as its causal explanation. Here we used an advanced null modelling approach to disentangle the interacting effects of geometric constraints and species richness gradients on the elevational range size of vascular plants. We collected extensive field data on elevational distribution for 728 vascular plant species occurring in the Ladakh region, Western Himalaya. We supplied these regional data with subcontinental elevational ranges extracted from the literature. Moreover, we used in situ measured temperatures to quantify temperature variability along an elevational gradient to test the climate variability hypothesis. Observed range size patterns were sensitive to methods used to quantify the average range size. Range truncation disproportionately affected regional ranges of low‐elevation species and resulted in spurious support of elevational Rapoport's rule. However, when the confounding effects of domain boundaries and richness gradient were controlled, our null models revealed only slight deviations from the random expectations of elevational range size patterns, contrasting with the prediction of the Rapoport's rule. In line with these findings, seasonal and diurnal temperature variability did not change with elevation. Synthesis. Geometric constraints combined with underlying species richness gradient create range size patterns seemingly supporting Rapoport's elevational rule. However, null models accounting for these effects indicate that the range size of vascular plants in the Himalayas does not increase with elevation. Given the universality of the geometric constraints and species richness gradient, our results suggest that these confounding factors must be controlled when testing Rapoport's rule. The null model approach described here provides an efficient tool to do that.

Repeatable mechanical energy absorption of ZnO nanopillars

We show that repeatable energy absorption can be obtained via the reversible wurtzite-to-hexagonal phase transformation of ZnO nanopillars at room temperature. The effect is demonstrated using molecular dynamics simulations and available experimental data. With uniaxial compressive strains up to 22.1% along the [0001] orientation, a ZnO nanopillar with a lateral dimension of 5.5 nm can produce average specific energy absorption on the order of 26.7 J g−1 under quasistatic cyclic loading and 11.1 J g−1 under rapid loading. The theoretical maximum of the specific energy absorption is 41.0 J g−1 which can be approached at nanopillars with lateral sizes above 55 nm. These values are comparable to that of widely used aluminum foams. The effects of inversion domain boundaries and sample size on the repeatable energy absorbing capacity are discussed. The findings open an avenue for ZnO nanostructures in mechanical energy absorption and dissipation applications.

Effect of Domain Size, Boundary, and Loading Conditions on Mechanical Properties of Amorphous Silica: A Reactive Molecular Dynamics Study.

Mechanical properties are very important when choosing a material for a specific application. They help to determine the range of usefulness of a material, establish the service life, and classify and identify materials. The size effect on mechanical properties has been well established numerically and experimentally. However, the role of the size effect combined with boundary and loading conditions on mechanical properties remains unknown. In this paper, by using molecular dynamics (MD) simulations with the state-of-the-art ReaxFF force field, we study mechanical properties of amorphous silica (e.g., Young’s modulus, Poisson’s ratio) as a function of domain size, full-/semi-periodic boundary condition, and tensile/compressive loading. We found that the domain-size effect on Young’s modulus and Poisson’s ratio is much more significant in semi-periodic domains compared to full-periodic domains. The results, for the first time, revealed the bimodular and anisotropic nature of amorphous silica at the atomic level. We also defined a “safe zone” regarding the domain size, where the bulk properties of amorphous silica can be reproducible, while the computational cost and accuracy are in balance.

Tailoring of stable induced domains near a charged domain wall in lithium niobate by probe microscopy

Ferroelectric lithium niobate (LiNbO3) crystals with an engineered domain structure have a number of applications in optical systems for generation of multiple laser radiation harmonics, acoustooptics, precision actuators, vibration and magnetic field sensors, including those for high-temperature applications, and prospectively, in non-volatile computer memory. We have studied the effect of charged domain boundary on the formation of induced domain structures in congruent lithium niobate (LiNbO3) crystals at the non-polar x-cut. Bi- and polydomain ferroelectric structures containing charged “head-to-head” and “tail-to-tail” type domain boundaries have been formed in the specimens using diffusion annealing in air ambient close to the Curie temperature and infrared annealing in an oxygen free environment. The surface potential near the charged domain wall has been studied using an atomic force microscope (AFM) in Kelvin mode. We have studied surface wedge-shaped induced microscopic domains formed at the charged domain boundary and far from that boundary by applying electric potential to the AFM cantilever which was in contact with the crystal surface. We have demonstrated that the morphology of the induced domain structure depends on the electrical conductivity of the crystals. The charged “head-to-head” domain boundary has a screening effect on the shape and size of the domain induced at the domain wall. Single wedge-shaped domains forming during local repolarization of reduced lithium niobate crystals at the AFM cantilever split into families of microscopic domains in the form of codirectional beams emerging from a common formation site. The charged domain wall affects the topography of the specimens by inducing the formation of an elongated trench, coincident with the charged boundary, during reduction annealing.

Domain-boundary independency of Raman spectra for strained graphene at strong interfaces

Strains in graphene play a significant role in graphene-based flexible devices, but many aspects of the domain boundary effects in strained graphene remain unclear, such as the evolution of Raman spectra. Here we present a systematic investigation on the domain boundary effects on the Raman spectra of strained graphene, using a designed strong interface formed by formvar resins. We achieve in single-crystal graphene by far the largest strain up to 2%, significantly improved from the previous highest value of 1.3%, as well as the redshift and splitting for its G and 2D peaks. More importantly, the Raman spectra of strained bi-crystal graphene with a domain boundary show that the spectral evolution follows the same trend as the single crystal, and this trend was also confirmed by the result in polycrystalline graphene, demonstrating that the straining effect on the G and 2D peaks of graphene at strong interfaces is actually independent of its domain boundaries, different from the previous report of graphene deposited on weak interfaces. We attribute it to the efficient interfacial stress transfer at the formvar interfaces, and believe they can provide new insights into the understanding of graphene mechanical behaviors and valuable guidance for graphene-based flexible electronics.

Microscopic observation of highly mobile charge carriers in organic transistors of semicrystalline conducting polymers

Charge carrier dynamics in organic field-effect transistors (OFETs) of semicrystalline conducting polymers poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) and poly(3-hexylthiophene) (P3HT) have been investigated down to 4 K by field-induced electron spin resonance (FI-ESR) spectroscopy. The highly mobile nature of charge carriers within the ordered regions of the polymers has been clarified from the observation of the motional narrowing effect of the ESR spectra even below 30 K, where device operation cannot be observed presumably owing to the effect of domain boundaries. The activation energy of carrier motion observed by ESR has been determined as 17 meV for PBTTT and 13 meV for P3HT, which are an order of magnitude smaller than that of FET mobility (>110 meV) obtained for the same devices. These results demonstrate that the intrinsic carrier mobility within the ordered region is much higher than that expected from the macroscopic transport measurements in the semicrystalline polymers.

Inversion domain boundaries in Mn and Al dual‐doped ZnO: Atomic structure and electronic properties

AbstractThe atomic and electronic structures of inversion domain boundaries in Mn‐Al dual‐doped ZnO (Zn0.89Mn0.1Al0.01O) have been investigated. Using atomic‐resolution scanning transmission electron microscopy, a head‐to‐head c‐axis configuration and cation stacking sequence of αβαβ|γ|αβαβ along the c‐axis were observed at the basal‐plane inversion domain boundary. Energy‐dispersive X‐ray spectroscopy and electron energy‐loss spectroscopy revealed significant localization of Mn and minor localization of Al at the basal‐plane inversion domain boundary. Based on experimental findings, a Mn‐doped basal‐plane inversion domain boundary slab model was constructed and refined by first principles calculations. The model is in agreement with atomic‐resolution images. The local electronic density of states of the slab model basal‐plane inversion domain boundary shows a hybridization of the Mn d and O p states within the valence band and localized Mn d states in the conduction band. The thermoelectric properties of Zn0.99−xMnxAl0.01O ceramics have been reported in a previous work. In this work, the effects of inversion domain boundaries on the thermoelectric properties are discussed. In comparison to Zn0.99−xMnxAl0.01O ceramics with x≤0.05, inversion domain boundaries in Zn0.89Mn0.1Al0.01O caused thermal and electrical conductivity reduction due to interface scattering of phonons and electrons. The Seebeck coefficient increased, suggesting electron filtering at inversion domain boundaries.

Effects of temperature on aging degradation of soft and hard lead zirconate titanate ceramics

Abstract This paper aims to study the effects of heat treatment temperatures on the aging degradation of piezoelectric properties, i.e. piezoelectric coefficient ( d 33 ) and planar electromechanical coupling factor ( k p ), in soft and hard PZT ceramics. Aging degradations of d 33 and k p of the samples were measured for 192 h prior to heat treatments. The samples were then treated at various temperatures equivalent to 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 times of the materials' Curie temperatures. Aging degradations of d 33 and k p of the heat-treated samples were observed continuously for 1128 h. The piezoelectric properties of the un-treated samples gradually decreased with aging time. Attenuation of d 33 and k p in the samples immediately after heat treatment increased with increasing heat treatment temperature. Moreover, aging degradation rate and relaxation time of the samples measured after heat treatments increased with increasing heat treatment temperature. Comparing to hard PZT ceramics, soft PZT demonstrated greater change of d 33 and k p immediately after heat treatments. Soft PZT also showed greater aging rate and aging time than those of hard PZT. From the overall results, it can be concluded that both material type and heat treatment temperature have effects on aging behaviors of PZT materials. Aging degradation was more pronounced in soft PZT and the samples treated at high temperatures. The observed aging behaviors of PZT materials were explained by the interaction between domains and defects of oxygen vacancies that leads to volume, domain and grain boundary effects.

Effect of screw threading dislocations and inverse domain boundaries in GaN on the shape of reciprocal-space maps.

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features.

Enhanced dielectric relaxations in spark plasma sintered CaCu3Ti4O12 ceramics

Dense CaCu3Ti4O12 ceramics were prepared by spark plasma sintering method. The microstructure and dielectric properties, especially the dielectric responses, were systematically investigated and compared to solid state sintering process. The spark plasma sintered CaCu3Ti4O12 ceramics with much smaller grain size represent a higher dielectric constant than ceramics sintered by traditional solid state sintering process at room temperature and below 10 kHz. This difference is proposed to be the results of the enhanced dielectric responses in spark plasma sintered CaCu3Ti4O12 ceramics. Two dielectric relaxations in low temperature range (150–212 K) with the activation energy of 0.174 eV and 95.8 meV respectively are detected in spark plasma sintered CaCu3Ti4O12 ceramics at low and high frequency respectively, which are caused by the intrinsic mechanisms in grain associated with ionization of oxygen vacancies (VO2+) and aliovalences of Ti and Cu ions clusters. The more distinct mid-temperature dielectric relaxation in spark plasma sintered CaCu3Ti4O12 ceramics is suggested to be the result of enhanced domain boundary effects, while the high-temperature dielectric relaxation is related to the grain boundaries. The enhanced dielectric constant and weakened temperature stability in spark plasma sintered CaCu3Ti4O12 ceramics were supposed to be the mutual function of dielectric relaxations at domain boundary and grain boundary, which can be due to the increased defects and barrier layers generated by the fast and low oxygen partial pressure of spark plasma sintering process.

Effects of Domain Boundaries on the Diffraction Patterns of One-Dimensional Structures

Motivated by diffraction experiments on the (2√3 x √3) R30◦ reconstructed Si(111) surface due to deposition of rare earth elements (Dy, Tb) and silicide formation, we analyse the splitting and non-splitting of superstructure diffraction spots. For this purpose, we model diffraction patterns for one-dimensional structures generated by the binary surface technique and use supercell models to keep the analysis simple. Diffraction patterns are calculated in the framework of the kinematical diffraction theory, and they are analyzed as a function of the domains and domain boundaries. Basic properties of the diffraction pattern are analyzed for model systems of a two-fold and a three-fold periodicity. The rules derived from these calculations are applied to the “real-world” system of Si(111)-(2√3 × √3) R30◦-RESix (RE = Dy or Tb). Depending on the combination of domains and domain boundaries of different types, a plethora of different features are observed in the diffraction patterns. These are analyzed to determine the sizes of both domain boundaries and domains from experimentally observed splitting of specific superstructure spots.

Fractal parameterization analysis of ferroelectric domain structure evolution induced by electron beam irradiation

The article presents some results of fractal analysis of ferroelectric domain structure images visualized with scanning electron microscope (SEM) techniques. The fractal and multifractal characteristics were estimated to demonstrate self-similar organization of ferroelectric domain structure registered with static and dynamic contrast modes of SEM. Fractal methods as sensitive analytical tools were used to indicate degree of domain structure and domain boundary imperfections. The electron irradiation-induced erosion effect of ferroelectric domain boundaries in electron beam-stimulated polarization current mode of SEM is characterized by considerable raising of fractal dimension. For dynamic contrast mode of SEM there was revealed that complication of domain structure during its dynamics is specified by increase in fractal dimension of images and slight raising of boundary fractal dimension.

Edge-tone effects and prosodic domain effects on final lengthening

This study reports two experiments that investigate the edge-tones and domain-specific effects on final lengthening. The study shows that in Cypriot Greek the following occur: (a) lengthening applies primarily on the syllable nucleus not the syllable onset, which suggests variety specific effects of lengthening; (b) lengthening depends on the edge-tones, namely, polar questions trigger more lengthening than statements and wh-questions; (c) lengthening provides support for at least two distinct prosodic domains over the phonological word, the intonational phrase and the intermediate phrase; greater lengthening associates with the first and shorter lengthening with the latter; (d) finally, syllable duration depends on the syllable distance from the boundary, i.e. lengthening locally applies on penultimates and ultimates whereas antepenultimates are affected the least. Additionally, by pointing to the distinct lengthening effects of edge-tones and domain-boundaries, the aforementioned findings highlight the application of different lengthening devices. Keywords: Prosodic structure; preboundary lengthening; edge-tone lengthening; Cypriot Greek

The effect of cation ordering and domain boundaries on low loss Ba(BI1/3BII2/3)O3 perovskite dielectrics revealed by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM)

High quality ceramics of Ba((Co0.7Zn0.3)1/3Nb2/3)O3 (BCZN), Ba(Mg1/3Nb2/3)O3 (BMN) and Ba(Mg1/3Ta2/3)O3 (BMT) were prepared by the mixed oxide route using sintering temperatures up to 1620 °C. Products with a high degree of cation ordering exhibited dielectric Q × f values from 83,000 GHz (BCZN) to 360,000 GHz (BMT). High Resolution TEM and aberration-corrected scanning transmission electron microscopy (STEM) revealed ordering domains and type I, II and III boundary structures. High-Angle Angular Dark Field (HAADF) STEM images provided direct evidence of 1:2 ordering and stacking sequences, and the presence of disordered regions within domain boundaries. The exceptionally high Q × f values for BMT are associated with a high degree of B-site ordering and the removal of domain boundaries in large, single domain grains. The catastrophic degradation of Q × f values in BMN after prolonged sintering is associated with formation of a lossy ferroelectric secondary phase (Ba3Nb2O8), and changes to composition and stoichiometry of BMN grains.

Dielectric abnormities in complex perovskite BaTi1−x(Co0.5Nb0.5)xO3 ceramics

Dielectric characteristics of BaTi1−x(Co0.5Nb0.5)xO3 (x=0.2, 0.4 and 0.6) ceramics are investigated together with mixed-valence structure. X-ray diffraction shows that all samples are cubic perovskite phase at room temperature. As the sintering temperature increases, grain size increases, accompanying obvious change in dielectric response. The samples with larger grains exhibit the giant dielectric characteristics, which are considered to be attributed to domain boundary effect. The frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of ~0.3eV, which is assigned to be the result of charge ordering.

Effect of Domain Boundaries on the Raman Spectra of Mechanically Strained Graphene

We investigate the effect of mechanical strain on graphene synthesized by chemical vapor deposition (CVD) transferred onto flexible polymer substrates by observing the change in the Raman spectrum and then compare this to the behavior of exfoliated graphene. Previous studies into the effect of strain on graphene have focused on mechanically exfoliated graphene, which consists of large single domains. However, for wide scale applications CVD produced films are more applicable, and these differ in morphology, instead consisting of a patchwork of smaller domains separated by domain boundaries. We find that under strain the Raman spectra of CVD graphene transferred onto a silicone elastomer exhibits unusual behavior, with the G and 2D band frequencies decreasing and increasing respectively with applied strain. This unusual Raman behavior is attributed to the presence of domain boundaries in polycrystalline graphene causing unexpected shifts in the electronic structure. This was confirmed by the lack of such behavior in mechanically exfoliated large domain graphene and also in large single-crystal graphene domains grown by CVD. Theoretical calculation of G band for a given large shear strain may explain the unexpected shifts while the shift of the Dirac points from the K point explain the conventional behavior of a 2D band under the strain.

Step and Domain Boundary Effect of Surface Reconstruction to Si(111)-√ 3×√3-Ag

The influence of step and domain boundary on growth of Si(111)-√ 3×√3-Ag has been studied in situ using optical surface second-harmonic generation and low energy electron diffraction. The second harmonic intensity shows a difference of about 50% for Si(111) surfaces with different miscut angles and domain boundary densities, although no significant difference has been observed in low energy electron diffraction patterns, indicating a significant impediment to the growth of Si(111)-√ 3×√3-Ag by step and domain boundaries. Simulation results reveal a 90% coverage of Si(111)-√ 3×√3-Ag on the vicinal substrate with an miscut angle of 0.41o, consistent with the dynamics of Ag atoms on Si(111)-7×7 surface. The influence of two dimentional adatom gas on surface structure has also been discussed.