Influence Of Lattice Defects Research Articles

Influence of Lattice Defects on Trans-Oligoene Substructure Formation in Graphene.

The photochemical reaction of iodine and graphene induces strong new Raman modes due to the formation of trans-oligoene substructures in graphene domains. This unique reactivity was demonstrated before on defect-free graphene, however leaving the influence of e. g. carbon vacancies, unexplored. Here, we investigate the photochemical reaction applied on graphene with varying average distances of lattice defects and statistically analyze the characteristic Raman modes which develop with the iodination reaction. We show that the iodination reaction does not lead to Raman-active defects and thus, the newly formed trans-oligoene substructures do not contribute to the D-mode of graphene. A statistical analysis reveals the correlation between the average distance of lattice defects and the intensity of the v1-mode. For defective graphene with average defect distances below ~1 nm no new Raman modes evolve, which is the lower limit of the substructure size probed at 532 nm and explains why this observation was not possible before using common graphene oxide as graphene source.

Influence of lattice defects on the high pressure properties of Ni0.66Mn2.34O4 NTC ceramics

The properties and hence the applications of negative temperature coefficient (NTC) oxides, NixMn3-xO4, strongly depend on the Ni:Mn ratio, valence states, defects and cation distribution in the spinel structure. Here, the accuracy of determination of nickel and manganese cations distribution in the spinel structure of Ni0.66Mn2.34O4 oxide, has been improved by taking into account the presence of tetrahedral vacancies. Additionally, the structural stability of cubic Ni0.66Mn2.34O4 was investigated as a function of pressure up to 9.5 GPa using synchrotron radiation angle-dispersive X-ray powder diffraction and a diamond anvil cell. The bulk modulus and its first derivative were determined by fitting the Birch-Murnaghan equation of state (EoS) model to the experimental pressure-volume data. Rietveld refinement of the X-ray powder diffraction data reveals that the cubic spinel structure is stable upon compression to 9.5 GPa. The XRD data yielded a bulk modulus of K0 = 126(7) GPa, with a pressure derivative K′ = 12(2). The obtained data were discussed in terms of defects in the cationic sublattice and compared with the elastic parameters of NiMn2O4.

Influence of Lattice Defects on the High Pressure Properties of Ni0.66mn2.33o4 Ceramics

Influence of Lattice Defects on the High Pressure Properties of Ni0.66mn2.33o4 Ceramics

The influence of lattice defects, recombination, and clustering on thermal transport in single crystal thorium dioxide

Thermal transport is a key performance metric for thorium dioxide in many applications where defect-generating radiation fields are present. An understanding of the effect of nanoscale lattice defects on thermal transport in this material is currently unavailable due to the lack of a single crystal material from which unit processes may be investigated. In this work, a series of high-quality thorium dioxide single crystals are exposed to 2 MeV proton irradiation at room temperature and 600 °C to create microscale regions with varying densities and types of point and extended defects. Defected regions are investigated using spatial domain thermoreflectance to quantify the change in thermal conductivity as a function of ion fluence as well as transmission electron microscopy and Raman spectroscopy to interrogate the structure of the generated defects. Together, this combination of methods provides important initial insight into defect formation, recombination, and clustering in thorium dioxide and the effect of those defects on thermal transport. These methods also provide a promising pathway for the quantification of the smallest-scale defects that cannot be captured using traditional microscopy techniques and play an outsized role in degrading thermal performance.

Relationship between lattice defects and phase transformation in hydrogenation/dehydrogenation process of the V60Ti25Cr3Fe12 alloy

The hydrogen storage capacities of vanadium-based solid solution alloys are determined by both bulk and surface characteristics. In this research, the influence of lattice defects and phase transformation of the ball-milled V60Ti25Cr3Fe12 alloy was investigated systematically. With the elongated ball milling time (0.5 h, 1 h, 2 h and 3 h), both the hydrogenation and dehydrogenation capacities decrease. XRD and TEM methods are applied to make the essential mechanism clearer. The XRD results demonstrate that after full hydrogenation, a large amount of VH2 phase and some V2H phase are observed, and the V2H phase proportion rises with the elongated ball milling time. The alloy particle size is limited in several micrometers, however, the XRD and subsequent TEM results demonstrate that unnegligible amorphous phase is formed in the surface layer (about 5 nm). The PALS and subsequent HRTEM results conformed that some defects (lattice deformation and dislocations/vacancies) appear in the bulk of the milled alloy particles. It is because of the defects and amorphous phase caused by ball milling that the formation of the monohydride is not been suppressed effectively in the hydrogen absorbing and desorbing process, and the defects can trap the hydrogen atoms, leading to the decrease of the hydrogen capacity. In addition, the phase transformation between V2H and VH2 is confined, thus a decrease of effective hydrogenation capacity is observed. As to the cyclic property, the micro-strains cannot be released by refining the particle size of the alloy particles by ball milling, thus, the hydrogen storage cyclic durability is not ameliorated.

Skyrmions and merons in two-dimensional antiferromagnetic systems

We have investigated (numerically) skyrmions constituted by two merons in two-dimensional Heisenberg antiferromagnets. The behavior and stability of these topological pseudo-particles are analyzed in discrete and finite lattices. The influence of lattice defects and external magnetic fields is also studied. The topological stability dictates that the two merons must be kept apart but processes of annihilation and fusion of merons are observed for finite lattices.

Influence of lattice defects on the ferromagnetic resonance behaviour of 2D magnonic crystals.

This paper studies, from a modelling point of view, the influence of randomly distributed lattice defects (non-patterned areas and variable hole size) on the ferromagnetic resonance behaviour and spin wave mode profiles of 2D magnonic crystals based on Ni80Fe20 antidot arrays with hexagonal lattice. A reference sample is first defined via the comparison of experimental and simulated hysteresis loops and magnetoresistive curves of patterned films, prepared by self-assembly of polystyrene nanospheres. Second, a parametric analysis of the dynamic response is performed, investigating how edge, quasi-uniform and localized modes are affected by alterations of the lattice geometry and bias field amplitude. Finally, some results about the possible use of magnetic antidot arrays in frequency-based sensors for magnetic bead detection are presented, highlighting the need for an accurate control of microstructural features.

Influence of lattice defects on the coherent interaction of photovoltaic lattice solitons

The influence of an optically induced waveguide lattice with a defect on the coherent interaction of one-dimensional lattice solitons (LSs) formed via the photovoltaic photorefractive effect is investigated by employing numerical simulations. The results show that the uniform lattice can keep the neighboring LSs propagating with constant spacing and can affect the energy transfer between them. Further research has shown that the energy transfer can be effectively controlled by adjusting the relative phase difference between neighboring LSs and by introducing a defect in the waveguide lattice.

Influence of Lattice Defects on the Grain Growth Kinetics of Nanocrystalline Fluorite

The growth process of nanocrystalline fluorite was studied by in situ synchrotron radiation X-ray diffraction. The two studied samples had comparable crystalline domain size, but quite different content of lattice defects as a result of the different preparation procedures: ball milling of coarse CaF2 powder or coprecipitation of CaCl2 and NH4F. It is shown that the high dislocation density in the ball-milled fluorite is responsible for a recrystallization process above 773 K (500 °C), which is not observed in the chemically synthesized fluorite. The linear thermal expansion coefficients of both nanocrystalline powders, as obtained and also from the in situ X-ray diffraction data, show a smaller increase with temperature than suggested by the literature on coarse-grained fluorite.

Influence of lattice defects on the reactivity of lithium titanate

7Li NMR spectroscopic experiments on Li2TiO3 demonstrate that the presence of planar crystal defects leads to lithium ion mobility in the temperature range of 30–100°C. Kinetics studies show the number of planar defects (and thus the rate of Li-H ion exchange) depends on the method and conditions of lithium titanate synthesis. The complete exchange of Li+ for H+ results in the formation of crystalline titanium oxyhydroxide TiO(OH)2 due to stabilization of defect state.

The impact of microstructural alterations at spray coated cylinder running surfaces of diesel engines – Findings from motor and laboratory benchmark tests

Future motor engine design and technology demand new materials that meet the requirements in terms of friction and wear properties. In order to reduce weight of the engine block and further more reduce the emissions thermal spray coatings are options to manufacture wear resistant and low-friction cylinder running surfaces. A motor cylinder with a thermally sprayed mild steel coating after a road test is prepared for transmission electron microscopy (TEM) investigations in the positions top dead center (TDC) and bottom dead center (BDC). In the dead centers of engines mixed/boundary lubrication conditions prevail. Within this study a new nanocrystalline thermal spray coating is investigated using two different laboratory tests where mixed/boundary lubrication regime is presumed. Conventional mild steel coatings and the new high alloyed Fe-base coatings are tested against two different piston rings in a reciprocating sliding wear test and an oscillating sliding wear test, known as SRV © test. TEM studies of the surface near microstructure demonstrate the difference in the microstructural alterations and wear mechanisms. Findings from the motor cylinder in surface and subsurface modifications are considered when discussing the results from laboratory tests in terms of initial grain size, influence of lattice defects and chemical influences due to oil additives.

The Influence of Lattice Defects on the Ground-State Properties of the Falicov-Kimball Model in Two Dimensions

The Influence of Lattice Defects on the Ground-State Properties of the Falicov-Kimball Model in Two Dimensions

Defect Control for Superior Properties in K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> Single Crystals

Single crystals of K0.47Na0.53NbO3 (KNN) and Mn-substituted KNN (Mn-KNN, K0.53Na0.47Mn0.004Nb0.996Oy) were grown by a flux method, and the influence of lattice defects on the polarization and leakage current properties was investigated. As-grown KNN did not show an apparent polarization hysteresis loop due to its large leakage current (~10-3 A/cm2). The substitution of 0.4%-Mn at the Nb site and subsequent annealing under a moderate oxidative condition were effective in suppressing the leakage current of KNN crystals. 0.4%-Mn-KNN annealed at 1100°C in air exhibited a low leakage current (~10-8 A/cm2), a relatively large remanent polarization of 40 μC/cm2 and a coercive field of 12 kV/cm at 25°C. The oxidation of Mn and Nb ions during annealing in air is found to play an essential role in the low leakage current of Mn-KNN.

Defect control for polarization properties in K0.5Na0.5NbO3 single crystals

Single crystals of K0.47Na053NbO3 (KNN) and Mu-substituted KNN (Mn-KNN, K0.53Na0.47Mn0.004Nb0.996Oy) were grown by a flux method, and the influence of lattice defects on the polarization and leakage current properties was investigated. As-grown KNN did not show an apparent polarization hysteresis loop due to its large leakage current (~10-3 A/cm2). 0.4 at.%-Mn-KNN annealed at 1100oC in air exhibited a low leakage current ( ~ 10-8 A/cm2), a relatively large remanent polarization of 40 microC/cm2 and a coercive field of 12 kV/cm at 25oC. The oxidation of Mn and Nb ions during annealing in air was found to play an essential role in the low leakage current in Mn-KNN. Mn substitution followed by annealing under moderate oxidation condition was effective for reducing leakage current in addition to enhancing polarization property.

The influence of lattice defects on fluorescence and phosphorescence in the europium aluminate EuAl 2 O 4

Alkaline-earth (M2+) aluminates MAl2O4 doped with Eu2+ show efficient fluorescence and phosphorescence. In this study the properties of the concentrated europium aluminate EuAl2O4 and of samples partially substituted with Ca2+, Sr2+, Ba2+ are investigated. X-ray diffraction data and a characterisation of the luminescence are presented. It is suggested that the deformation of the local environment of the Eu2+ due to incorporated defects is the reason for both phenomena of fluorescence and phosphorescence. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Efficient free-energy calculations by the simulation of nonequilibrium processes

Discusses a particular application of computational physics: the calculation of thermodynamic properties by computer simulation methods. More specifically, we focus on one of the most difficult tasks in this context: the estimation of free energies in problems such as the study of phase transformations in solids and liquids, the influence of lattice defects on the mechanical properties of technological materials, the kinetics of chemical reactions, and protein-folding mechanisms in biological processes. Because the free energy plays a fundamental role, the development of efficient and accurate techniques for its calculation has attracted considerable attention during the past 15 years and is still an active field of research. We discuss some general aspects of equilibrium and nonequilibrium approaches to free-energy measurement and present the reversible scaling technique which we have recently developed.

Intrinsic frustration effects in anisotropic superconductors

Lattice distortions in which the axes are locally rotated provide an intrinsic source of frustration in anisotropic superconductors. A general framework to study this effect is presented. The influence of lattice defects and phonons in $d$ and $s+d$ layered superconductors is studied.

Influence of defects on the modulated phases of bccd

Abstract The influence of lattice defects on the incommensurate and commensurate phases of betaine calcium chloride dihydrate (BCCD) has been studied on Br doped crystals BCC1−x B x D with x <m 0.38 by means of dielectric and IR—spectroscopic investigations between 20 and 250 K under hydrostatic pressures up to 400 MPa.

Third molecular continuum in VUV radiation of solid Ar

The emission of the third continuum of solid Ar has been studied at excitation by electron beam. The influence of lattice defects and oxygen-containing species is examined. Glow curves of solid Ar are measured for the samples with different content of lattice defects. The role of electron traps in a population of excited state emitting the third continuum is established and recombination processes of radiative centers are found. The results obtained provide some evidence of ionic nature of the centers involving in emission of the third continuum in solid Ar. It is supposed that the radiative decay of the ionic excimer Ar 2 2+ contributes mainly to the third continuum.

Dark-current analysis of InGaAs-MSM-photodetectors on silicon substrates

We fabricated In/sub 0.53/Ga/sub 0.47/As metal-semiconductor-metal (MSM) photodetectors on lattice-mismatched [001]Si substrates in order to analyze the influence of lattice defects on the III-V semiconductor device properties. The growth procedure and the device-fabrication process are described. The low native Schottky-barrier of InGaAs is enhanced by a p/sup +/n-InP double layer. Dark-current densities in the operation range measured with the lattice-mismatched devices are comparable to those of lattice-matched devices on InP. Their statistical distribution proves the good reproducibility of the fabrication process. From the temperature and voltage dependence of the dark current, we find that on Si the current in the medium voltage range is obviously influenced by defect-related centres in the bandgap. An empirical model is presented to describe the experimental findings. The dark current is low enough for applications of the MSM detectors in optoelectronic systems.