Influence Of Point Defects Research Articles

The influence of point defects on the sintering of magnesium oxide

The influence of point defects on the sintering of magnesium oxide

Defect-induced modifications in electronic and thermoelectric properties of pentagonal PdX2 (X = Se, S) monolayers

The point defects induced in crystalline solids during the growth process unintentionally or doped intentionally after the growth process significantly modify their properties. The intentionally controlled doping of point defects in crystalline solids has been widely used to tune their properties. In this paper, we investigate the effect of vacancy and substitutional point defects on the electronic and thermoelectric properties of pentagonal PdX2 (X = Se, S) monolayers using the density functional theory (DFT) and semi-classical Boltzmann transport theory. We find that the point defects in pentagonal PdX2 (X = Se, S) monolayers modify their electronic structures. The contributions of d orbitals of Pd atoms and p orbitals of Se/S atoms are significantly affected due to the presence of point defects in the lattice. The defect states are appeared within the band gap region which effectively reduces the band gap of the monolayer. These defect states could be helpful in tuning the electrical and optical properties of the monolayer. The defect states appear within the band gaps of defective monolayer structures which effectively modifies the electronic properties of these monolayer structures. The transport calculations show that the presence of the point defects in the lattice reduces the thermoelectric performance of these PdX2 monolayers. Both the Seebeck coefficient and electrical conductivity show deteriorated behaviour under the influence of point defects in the lattice. Thus, the influence of these defects must be carefully taken into account while fabricating these materials for practical applications.

The influence of point defects on the electronic structures and optical properties of 3C-SiC

Using first-principles calculations, we studied the formation energy of point defects in cubic silicon carbide (3C-SiC) and the influences of defects on its electronic band structure, density of states, and optical properties. We found that the formation energy of the interstitial defect is greater than that of the vacancy and antisite defect, with the Si interstitial defect having the highest formation energy. The electronic band structure and density of states have no bandgap due to the vacancy defect, interstitial defect, and Si antisite defect (Si atom occupies the position of C atom), while the changes due to the C antisite defect (C atom occupies the position of Si atom) are not significant. Depending on the type of defect, the optical properties change differently, with the vacancy defect having the most significant impact on the optical properties. The vacancy defect notably increases the optical conductivity, dielectric function, reflectivity, extinction coefficient, and refractive index in the low-energy region, indicating the potential application of 3C-SiC in the field of optoelectronic devices.

Effects of intrinsic point defects (Tii-Vo) on the photocatalytic performance of bilayer rutile/anatase TiO2

Despite the progress on the photocatalytic performance of TiO2 as a typical photocatalytic material, previous research has overlooked the systematic study of the coexistence of Tii and Vo on the photocatalytic property of rutile or anatase TiO2 with bilayers. Studies on the comparative photocatalytic property of these materials have been rarely reported. Thus, the influences of point defects (Tii-Vo) on the photocatalytic performance of bilayer rutile or anatase TiO2 were investigated by GGA + U calculations under density general function theory framework. Results showed that the bilayer rutile Ti24TiiO47 (1 1 0) system exhibited the highest relative stability, strong carrier activity, reduced carrier recombination, and the longest lifetime. Furthermore, the absorption spectrum is clearly red shifted. This system is beneficial for the dissociation of water to produce H2 and O2. This research provides certain theoretical reference value on the design and fabrication of novel bilayer rutile TiO2(1 1 0) surface photocatalysts.

Influences of point defects on electron transport of two-dimensional gep semiconductor device

The quantum transport properties of defective two-dimensional (2D) GeP semiconductor nanodevice consisting of typical point defects, such as antisite defect, substitutional defect, and Schottky defect, have been studied by using density functional theory combined with non-equilibrium Green’s function calculation. The antisite defect has indistinctive influences on electron transport. However, both substitutional and Schottky defect have introduced promising defect state at the Fermi level, indicating the possibility of improvement on the carrier transport. Our quantitative quantum transport calculations of I–V b behavior have revealed that the electrical characters are enhanced. Moreover, the P atom vacancy could induce significant negative differential resistance phenomenon, and the physical mechanism is unveiled by detailed analysis. The transfer characteristic properties could be prominently improved by substitutional defect and vacancy defect. Most importantly, we have proposed a computational design of GeP-based electronic device with improved electrical performance by introducing vacancy defect. Our findings could be helpful to the practical application of novel 2D GeP semiconductor nanodevice in future.

First Observation of Quantum Diffusion in Non-Cubic Metal: Deuterium Diffusion in In

Diffusion of deuterium in indium is studied herein. In the temperature range 200–350 K, mass transfer is controlled predominantly by the mechanism of overbarrier atomic jumps; at temperatures from 80 to 120 K, by tunneling; whereas in the range from 120 to 200 K, there takes place a gradual transition from one migration mechanism to the other. These results are of fundamental significance since it is shown for the first time that quantum diffusion can be observed in a metal with a crystal lattice other than the body centered cubic one. Conditions are specified that are necessary for the observation of quantum diffusion of hydrogen: low values of Debye temperature, density of atomic packing in the lattice, and distance between the nearest equilibrium positions of hydrogen atoms. Moreover, data on the influence of point defects on hydrogen tunneling in solids are gained for the first time as well. The quantum diffusion coefficient is twice as high in the sample with enhanced vacancy concentration.

Influence of point defects and multiscale pores on the different phonon transport regimes

A common strategy to tailor the thermal conductivity of a material is to introduce structural features that modulate phonon scattering, such as atomic-scale defects and nano- and macro-sized pores. However, particle-like and wave-like phonon transport and scattering during a crossover in thermal transport regimes is not well understood. Here, we perform a rigorous quantitative comparison of the thermal conductivity obtained from molecular dynamics simulations and phonon Boltzmann transport equations, taking graphene as an example. We observe a generally increasing trend in thermal conductivity when the pore size increases from point defect to nanopore, due to a transition from Rayleigh scattering to geometric scattering and reduced boundary density. The thermal conductivity further converges to the diffusive limit for macropores because of the dominant effect of phonon-phonon scattering over phonon-boundary scattering. Moreover, we identify a critical interpore distance for the crossover from dependent to independent phonon-pore scattering and a critical pore size for the crossover from point defect scattering to boundary scattering. This work provides a comprehensive understanding of phonon transport in materials containing defects and pores.

Simulation of Point Defects Formation in the Fuel Element of a Nuclear Power Plant’s Wave Reactor

This paper considers the point defects that influence the operation of a wav nuclear power reactor with a uranium fuel medium. The formed individual point defects or such defect groups can produce a perturbing effect on the stability of the nuclear reactor operating mode and involve its transition to an unstable state. Studies have been carried out on the effect on the characteristics of the nuclear burnup wave in a medium with neutron multiplication for 2D geometry. For the calculation, the uranium-thorium fissile medium has been considered. The parametric calculations were carried out with 235 U different enrichment percents and different values of neutron activation energy. At that, it was assumed that the wave (flow) reactor stable operation region is located in the range of activation energies from 10–3 eV to 1 eV or in the region from 2 MeV to 8 MeV. When calculating the neutron flux intensity in a wave reactor, the influence of point defects and their aggregates on the decelerating elastically scattered neutrons’ flux density and the flux density of decelerating non-elastically scattered neutrons was considered. The dependences of the point defects formation rate on the medium fissile temperature for several compositions of the uranium-thorium medium are obtained. As visually identified, the graphic materials obtained during the calculations are similar to the photos of fuel rods after the energy campaign.

“Influence of point defects on the hydrogen storage in nickel decorated GeC and SnC nanotubes’’

The density functional theory (DFT) calculations were performed to investigate the structures, electronic properties, and hydrogen-storage capacity of Ni- decorated GeCNT and SnCNT, as well as the effect of Ge, Sn and C vacancies on hydrogen storage capacity. The functionalized Ni is found to be adsorbed on GeCNT, SnCNT, GeCVCNT and SnCVCNT with an adsorption energy of −6.453, −3.780, −5.794 and −4.845 eV. The functionalized GeCNT, SnCNT, GeCVCNT and SnCVCNT bind up to seven, four , five and four hydrogen molecules with the adsorption energy of (-0.236, −0.208, −0.221 and −0.201 eV). The GeCNT, SnCNT, GeCVCNT and SnCVCNT systems exhibit a maximum gravimetric storage capacity of 8.963, 4.083, 6.582 and 4.089 wt%. Our calculations show that nH2NiGeCVGe and nH2NiSnCVSn system is not a suitable use for hydrogen storage. Therefore, Ni-decorated GeCNT, SnCNT, GeCVCNT and SnCVCNT nanotubes are promising candidate materials for use as hydrogen storage material.

Influence of Point Defects on the Equilibrium Concentration of Interstitial Oxygen in Crystalline Silicon

The effect of excess point defects on the equilibrium concentration of interstitial oxygen for the system of interstitial oxygen/SiO2 precipitates in crystalline Si is theoretically investigated. The expression for the equilibrium concentration of interstitial oxygen in Si modified by the excess point defects is derived. Excess vacancies in Si are found to decrease this concentration, while the excess Si self-interstitials have the opposite effect. The effects of different conditions for the point defect generation on the equilibrium in the system of interstitial oxygen/SiO2 precipitates in crystalline Si are studied.

Influence of Point Defects on the Hydrogen Storage in Nickel Decorated Gec and Snc Nanotubes

Influence of Point Defects on the Hydrogen Storage in Nickel Decorated Gec and Snc Nanotubes

Influence of Point Defects on the Hydrogen Storage in Nickel Decorated Gec and Snc Nanotubes

Influence of Point Defects on the Hydrogen Storage in Nickel Decorated Gec and Snc Nanotubes

Terahertz Characterization of Lead-Free Dielectrics for Different Applications.

In this spotlight on applications, we describe our recent progress on the terahertz (THz) characterization of linear and nonlinear dielectrics for broadening their applications in different electrical devices. We begin with a discussion on the behavior of dielectrics over a broadband of frequencies and describe the main characteristics of ferroelectrics, as they are an important category of nonlinear dielectrics. We then move on to look at the influence of point defects, porosities, and interfaces, including grain boundaries and domain walls, on the dielectric properties at THz frequencies. Based on our studies on linear dielectrics, we show that THz characterization is able to probe the effect of porosities, point defects, shear planes, and grain boundaries to improve dielectric properties for telecommunication applications. Further, we demonstrate that THz measurements on relaxor ferroelectrics can be successfully used to study the reversibility of the electric field-induced phase transitions, providing guidance for improving their energy storage efficiency in capacitors. Finally, we show that THz characterization can be used to characterize the effect of domain walls in ferroelectrics. In particular, our studies indicate that the dipoles located within domain walls provide a lower contribution to the permittivity at THz frequencies than the dipoles present in domains. The new findings could help develop a new memory device based on nondestructive reading operations using a THz beam.

DFT-Based Studies on Carbon Adsorption on the wz-GaN Surfaces and the Influence of Point Defects on the Stability of the Diamond-GaN Interfaces.

Integration of diamond with GaN-based high-electron-mobility transistors improves thermal management, influencing the reliability, performance, and lifetime of GaN-based devices. The current GaN-on-diamond integration technology requires precise interface engineering and appropriate interfacial layers. In this respect, we performed first principles calculation on the stability of diamond–GaN interfaces in the framework of density functional theory. Initially, some stable adsorption sites of C atoms were found on the Ga- and N-terminated surfaces that enabled the creation of a flat carbon monolayer. Following this, a model of diamond–GaN heterojunction with the growth direction [111] was constructed based on carbon adsorption results on GaN{0001} surfaces. Finally, we demonstrate the ways of improving the energetic stability of diamond–GaN interfaces by means of certain reconstructions induced by substitutional dopants present in the topmost GaN substrate’s layer.

Influence of Point Defects on the Initiation of Electromigration in an Impurity Conductor

Influence of Point Defects on the Initiation of Electromigration in an Impurity Conductor

Room-temperature oxygen vacancy migration induced reversible phase transformation during the anelastic deformation in CuO

From the mechanical perspectives, the influence of point defects is generally considered at high temperature, especially when the creep deformation dominates. Here, we show the stress-induced reversible oxygen vacancy migration in CuO nanowires at room temperature, causing the unanticipated anelastic deformation. The anelastic strain is associated with the nucleation of oxygen-deficient CuOx phase, which gradually transforms back to CuO after stress releasing, leading to the gradual recovery of the nanowire shape. Detailed analysis reveals an oxygen deficient metastable CuOx phase that has been overlooked in the literatures. Both theoretical and experimental investigations faithfully predict the oxygen vacancy diffusion pathways in CuO. Our finding facilitates a better understanding of the complicated mechanical behaviors in materials, which could also be relevant across multiple scientific disciplines, such as high-temperature superconductivity and solid-state chemistry in Cu-O compounds, etc.

Influence of point defects on phase transformation and optical properties of TiO2 thin films via multilayering deposition technique

Thin anatase TiO2 films with preferential (004) orientation were successfully fabricated via multilayering technique, growth and stop repeatedly, using DC-magnetron sputtering and annealed at a relatively low temperature. The multilayering deposition technique suppressed the number of oxygen vacancy defects in TiO2 films without interrupting the columnar growth. The main columnar structure oriented along (101) plane and along (004) plane. Confirmed by the texture coefficient, the preferential (004) orientation of TiO2 films increased with increasing number of compact layers and the highest value was observed for post-annealed films at 200 °C. The surface morphology analysis indicated that the increase of surface roughness with increasing number of compact layers was related to the promotion of crystallization. The optical properties of multilayer films revealed that high number of compact layers greatly enhanced their absorption in the entire visible region, expanded energy band gap and increased refractive index.

Influence of point defects and grain boundaries on plasticity and phase transition in uniaxially-compressed iron

Using Molecular Dynamics (MD) computations we have reported recently a shear stiffening (hardening-like) effect in [001]-oriented defect-free iron single crystal. This effect makes shift the structural phase transition to a particularly high pressure level under ramp compression, but not under shock compression, so that the question arises about the essential role of the compression path and wave evolution in the solid state response including phase transition. Here, plasticity and phase transition are studied for iron samples under non-equilibrium uniaxial compression. Our focus is put on the effects of grain size and point defects such as atoms vacancy. Consistently with our previous results, it is found that, after yielding via twinning, both defect-free and defective iron single crystals exhibit a hardening-like effect while the twins progressively recede upon further compression and no dislocations activity is detected. This leads to mounting of the deviatoric stress. Yet, the transition onset pressure shift and temperature behavior are found to be defect-density dependent. Considering polycrystalline lattice, plasticity consists in complex interplay of intra-grain twinning and dislocation activities from grain boundaries. The elastic stiffening is attenuated now as compared to single crystal so that the phase transition is found to occur at much lower pressure in polycrystalline iron.

Structure-resistive property relationships in thin ferroelectric BaTiO_{3} films

A combined study of local structural, electric and ferroelectric properties of SrTiO_{3}/La_{0.7}Sr_{0.3}MnO_{3}/BaTiO_{3} heterostructures was performed by Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy in the temperature range 30–295 K. The direct correlation of film structure (epitaxial, nanocrystalline or polycrystalline) with local electric and ferroelectric properties was observed. For polycrystalline ferroelectric films the predominant polarization state is defined by the peculiarity of screening the built-in field by positively charged point defects. Based on Scanning Tunneling Spectroscopy results, it was found that a sequent voltage application provokes the modification of local resistive properties related to the redistribution of point defects in thin ferroelectric films. A qualitative analysis of acquired Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy images together with Scanning Tunneling Spectroscopy measurements enabled us to conclude that in the presence of structural defects the competing processes of electron injection, trap filling and the drift of positively charged point defects drives the change of resistive properties of thin films under applied electric field. In this paper, we propose a new approach based on Scanning Tunneling Microscopy/Spectroscopy under ultrahigh vacuum conditions to clarify the influence of point defects on local resistive properties of nanometer-thick ferroelectric films.

Effect of Point Defects on the Tensile and Thermal Characteristics of Nickel–Aluminum Nanowire through Molecular Dynamics

The point defect has profound effect on the tensile characteristics such as yield stress and yield strain of any material. In this study, the influence of point defect (1%, 1.5% and 2%) on Ni–Al (B2 crystal structure) nanowire has been analyzed through molecular dynamics simulation. The uniaxial tensile load of 6 × 108/s has been applied along [001] direction under various temperature conditions such as 300 K, 450 K and 600 K to analyze the resulting outcomes which arise from the point defects and temperature and found that the increase in point defect concentration leads to the decline of the yield stress by around 9.7%, 13.2% and 17.42%, respectively, under ambient temperature condition (300 K). Besides, the increase in temperature under the same point defect concentration leads to the drop of the yield stress significantly. In addition to the above, it has been found that the point defect has a higher influence on the tensile characteristics of nanowire followed by the temperature effect.