Effect Of Lattice Defects Research Articles

Effect of lattice defects on crystal structure and microwave properties of Ba(Ga1/2Ta1/2)O3 doped Ba(Zn1/3Nb2/3)O3 ceramics

Traditionally, B-site cation ordering structure in Ba(B′1/3B″2/3)O3 based ceramics with complex perovskite structure is considered to be the dominant factor in determining the dielectric loss. The crystal structure of BZN-BGT ceramics changes to the B-site disordering from B-site 1:2 ordering accompanying with remarkably reduced dielectric loss. Ba(Ga1/2Ta1/2)O3 doping also inhibits the formation of Nb-rich secondary phases induced by Zn volatilization on the surface of BZN-BGT ceramics as well. The conductive activation energy Ea, an energy required for electrons to escape from the traps, increases to 0.55 eV from 0.40 eV, indicating the decrease of lattice defects concentration. As Ba(Ga1/2Ta1/2)O3 doping concentration increases, the dielectric thermal relaxation process of BZN-BGT ceramics weakens and the electrical conductivity decreases. These results indicate that the dielectric loss of BZN-BGT ceramics containing volatile Zn could be controlled by the lattice defects and secondary phases rather than B-site 1:2 ordering structure.

Defect-mediated structural phase transition in Ta2NiSe5 visualized via in situ TEM

Extensive experimental and theoretical efforts have been devoted to elucidating the origin of either structural or electronic instability in the formation of excitonic state in Ta2NiSe5, whereas the effects of lattice defects on actual structural phase transition in Ta2NiSe5 remain elusive. Here, we perform in situ transmission electron microscopy (TEM) experiments to investigate the structural phase transition of Ta2NiSe5 thin films, with a particular focus on the influence of microstructural features and lattice defects on the phase transition. In the cyclic in situ heating-cooling TEM experiments, we track the reversible orthorhombic to monoclinic (vice versa) phase transitions via twinning variant contrast in TEM images and via changes in reflection splitting in diffraction patterns. We further investigate the effects of dislocations and grain boundaries on the phase transition of Ta2NiSe5 thin films. Our findings reveal that individual dislocations can inhibit the transition from monoclinic to orthorhombic phases while simultaneously promoting the reverse transition from orthorhombic to monoclinic phases. Furthermore, we observe a phenomenon of metastable to stable phase transition within grain-boundary-confined regions of Ta2NiSe5 thin films. These in situ TEM observations offer a comprehensive microscopic perspective on defect-mediated phase transitions in Ta2NiSe5. This insight may extend to other varieties of transition-metal chalcogenides, thus implying a broader applicability.

Effect of lattice defects on electronic structure and thermoelectric properties of 2D monolayer MoS2

Molybdenum disulfide (MoS2) is considered as a promising economical and non-toxic thermoelectric material due to its low thermal conductivity and high Seebeck coefficient. However, its power factor is not ideal, which limits its energy conversion efficiency in thermoelectric applications. In this paper, the electronic structure of pure and lattice-defect MoS2 2D monolayer is studied by using the first principles method and non-equilibrium Green's function (DFT-NEGF). The effects of atom substitution and vacancy defect on the thermoelectric properties of MoS2 2D monolayer are also investigated. The result shows that the S-vacancy changes the bandgap by introducing donor and acceptor levels, while the substitution of Se and Te atoms slightly increases the bandgap value. In the case of n-type doping, the ZT value of the S atom substituted MoS2 reaches 1.19 at 300 K, while the Te atom substitution MoS2 has a higher ZT value of almost 2.26 at 800 K. The analysis shows that the thermal conductivity of MoS2 decreases due to the presence of S-vacancy, while the atomic substitution of Se and Te increases the power factor of MoS2. This work may provide a new method and theoretical guidance for achieving high performance of thermoelectric devices in the energy industry.

A DFT study on the effect of lattice defects on the electronic structures and floatability of spodumene

The influences of lattice vacancies and lattice impurities on the electronic structures and floatability of spodumene were studied by the density functional theory (DFT) through analysis of partial density of states (DOS), Mulliken population, differential charge density, and frontier molecular orbitals. The calculation indicated that the effect of lattice Al, Si, and Li vacancies on the DOS, Mulliken population as well as the interaction between spodumene and oleate was insignificant. Cr, Fe, and Mn impurities caused the shift of Fermi level towards lower energy and the occurrence of peaks of impurity near Fermi level. K and Na impurities contributed little to the lowest unoccupied molecular orbital (LUMO) of spodumene, while Cr, Fe, and Mn impurities had great contribution, suggesting that Cr, Fe, and Mn impurities significantly affected the interaction between spodumene and oleate. The frontier molecular orbitals analysis indicated Cr, Fe, and Mn impurities are in favor of oleate adsorption.

Effect of lattice defects on electronic structure and thermoelectric properties of two- dimensional WS2 materials

WS2 is a kind of thermoelectric material with great development potential that is used for thermoelectric power generation and refrigeration. In this study, the NEGF-DFT method was used to study the thermoelectric properties of intrinsic 2D-WS2 and the effects of periodic vacancy or substitution atoms on their electronic structure and thermoelectric properties. The results show that the ZT value of p-type 2D-WS2 is better than that of n-type 2D-WS2. The thermoelectric properties of p-type 2D-WS2 and p-type 2D-WS2 with O-atom replacing S-atom are better than those of the corresponding n-type 2D-WS2, while the thermoelectric properties of n-type 2D-WS2 with periodic defects and n-type 2D-WS2 with Se-atom or Te-atom replacement for S-atom are better than those of the corresponding p-type 2D-WS2. The ZT values of n-type 2D-WS2 with periodic defects, n-type 2D-WS2 with Se-atom replacement for S-atom, and n-type 2D-WS2 with Te-atom replacement for S-atom are 2.973, 3.383, and 3.0413, respectively, which indicates 2D-WS2 with Se-atom replacement for S-atom has the best thermoelectric performance.

Effect of lattice defects, hydrogen impurity and temperature on electronic thermal conductivity in first wall tungsten materials

Significant changes in the microstructure of the first wall tungsten (W) materials caused by intense particle irradiation from the plasma in fusion reactors should affect the thermal property of the first wall materials. Although it has been established that for metals including W, the electrons contained therein play a major role in heat transport, few theoretical studies have focused on the heat transport performance by electrons of the defective tungsten. In this work, we have intensively investigated the effect of irradiated defects and temperature on the electronic thermal conductivity of tungsten by the tight-binding (TB) potential model. It is found that the electronic transport performance of tungsten crystals with different defects, such as point defects, voids, or hydrogen (H) impurities, degrades with increasing defect concentration, where the greatest reduction is caused by the randomly-distributed point defects and the smallest by H at the same defect concentration. Importantly, filling H in the void is beneficial to reduce the scattering of the void against electrons and improve electronic transport performance. As the temperature rises, the electrical conductivity decreases, but the electronic thermal conductivity increases. The behavior in the electronic thermal conductivity is attributed to the additional ‘gain effect’ of temperature on the electronic thermal conductivity compared to the electrical conductivity. Besides, it is inferred that the weaker the electron scattering caused by defects, the slighter the response of electronic thermal conductivity to temperature. For all concerned systems, the changes in their electronic transport performance can be understood through our calculated electron mean free path (MFP).

Intrinsic thermoelectric properties in biphenylene nanoribbons and effect of lattice defects

Intrinsic thermoelectric properties in biphenylene nanoribbons (BNRs) and effect of lattice defects are investigated by employing the nonequilibrium Green’s function. A comparative analysis on intrinsic thermoelectric properties between graphene nanoribbons (GNRs) and BNRs is performed. Results show that although the Seebeck coefficient of BNRs is lower than that of the corresponding GNRs, BNRs exhibit better thermoelectric properties than the corresponding GNRs due to the lower phonon thermal conductance of BNRs. It is also shown that the lattice defects can enhance the maximum ZT (ZTmax) in armchair BNRs (ABNRs) and zigzag BNRs (ZGNRs), where the ZTmax can be up to 1.1 and 0.4 at T = 300 K, respectively. Moreover, such the enhancement in defective ZBNRs is more remarkable than that in defective ABNRs. Theoretical analysis reveals that this enhancement of the ZTmax originates from the substantial reduction of phonon thermal conductance due to the strong backscattering by the highly localized phonon states around the lattice defects.

Effect of Lattice Defects on the Electromigration-Induced Instability of the Interface between Joined Conductive Materials

Effect of Lattice Defects on the Electromigration-Induced Instability of the Interface between Joined Conductive Materials

Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP Added PAO Lubrication in Nanostructured Steels

Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP Added PAO Lubrication in Nanostructured Steels

Effect of lattice defects on the plastic Poisson's ratio of nanoporous gold

Nanoporous gold (np-Au) exhibits variations in the value of the plastic Poisson's ratio, νp – ranging from negative to positive – often for similar relative densities and ligament diameters. We investigate the effect of pre-existing lattice defects on νp of np-Au using molecular dynamics simulations. Uniaxial compression of np-Au samples that have the same porous morphology, but distinct defect densities, shows that a high density of pre-existing defects reduces νp. We interpret this observation by linking nanoscale tension-compression asymmetry in individual ligaments to the synergistic interplay between defects and surfaces, and ultimately to the plastic transverse coupling in np-Au.

A Molecular Dynamics Study on the Effects of Lattice Defects on the Phase Transformation from BCC to FCC Structures

Molecular dynamics simulations of the phase transformation from body- centered-cubic (bcc) to face-centered-cubic (fcc) structures were performed. A Morse-type function was applied, and the parameters were determined so that both fcc and bcc structures were stable for the perfectcrystal model. When the fcc structure was superior to the bcc structure, the bcc model transformed to fcc. Two mechanisms, based on the Bain and Nishiyama- Wasserman (NW) relationships, were considered. Then, point or linear lattice defects, i.e., randomly scattered or regularly aligned vacancies, were introduced. Consequently, bcc models tended to transform to an fcc structure, whereas fcc models remained stable. The transformation process was also investigated in detail. BCC-to-FCC transformation is often considered as a homogeneous process based on changes in the axis lengths, and such a process was observed for the perfectcrystal model. Conversely, for the defect models, local heterogeneous deformation patterns, including cylindrical domain and planar interface formation, were observed. These behaviors are considered to be related to plastic deformation during phase transformation, and the validity of the presented model for further investigation was confirmed.

Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP added PAO Lubrication in Nanostructured Steels

Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP added PAO Lubrication in Nanostructured Steels

Effect of lattice defects in vibration properties of nano-mechanical mass sensor using graphene

Effect of lattice defects in vibration properties of nano-mechanical mass sensor using graphene

Preparation and thermophysical properties of Ti4+ doped zirconia matrix thermal barrier coatings

There is an upper limited temperature of about 1200 °C for yttrium oxide partially stabilized zirconia coatings. With the increasing temperature of inlet gas (>1200 °C), new thermal barrier coatings are urgently needed to replace traditional yttrium oxide partially stabilized zirconia. Ti4+ ion doping has been recognized as an effective method to achieve this. In this work, a novel ceramic coating with low thermal conductivity at 1600 °C is synthesized, and the microstructure, chemical components, phase structures are analyzed. The thermal diffusivity and thermal conductivity of the as-sprayed coatings initially exhibited low values up to 1600 °C. The mechanism of low thermal conductivity is analyzed. The oxygen vacancies effectively reduce thermal conductivity, which can be proved by the ablation experiment (at 1600 °C). The effect of lattice defects caused by differences in the masses and radii of Ti4+ and Zr4+ ions on the phonon scattering coefficient is analyzed quantitatively. These results indicate that this coating is a promising candidate for thermal barrier coatings at high temperatures.

Lattice defects and oxide formation coupledly enhanced giant electrical resistance change in nanoporous silver

The electrochemically induced electrical resistance response of nanostructured metallic materials is an important issue in interdisciplinary fields including electrochemistry, physics and surface science. Nanoporous metals possess an open three-dimensional bicontinuous ligament (nanowire network)-channel (nanopore) structure with high surface-to-volume ratios, and show great potentials for investigations in this topic. Here we fabricate nanoporous silver (NPS) with high density of lattice defects (dislocations, twins, stacking defaults and grain boundaries) and ligaments composed of Ag nanocrystals with sizes comparable to the ligament length scale. More importantly, the present NPS shows extraordinarily enhanced reversible resistance response to electrochemical stimuli in alkaline electrolytes. A giant reversible resistance change of up to ∼1100% has been achieved in NPS. Moreover, the reversible electrical resistance change of NPS can be well modulated through cyclic voltammetry or square wave potential input. The related mechanisms have been rationalized on the basis of reversible oxide formation/reduction on the ligament surface of NPS, silver dissolution, as well as the effects of lattice defects in NPS.

Effects of Lattice Defects and Niobium Doping on Thermoelectric Properties of Calcium Manganate Compounds for Energy Harvesting Applications

We have investigated the thermoelectric (TE) properties of Ruddlesden–Popper (RP) CaO(CaMnO3)mn-type compounds, to be applied for TE waste heat recovery at elevated temperatures. We prepared several Nb-doped and undoped CaO(CaMnO3)m compounds having different CaO planar densities by controlling the Ca content via solid-state reaction, and characterized the resulting microstructures by x-ray diffraction analysis and high-resolution scanning electron microscopy. The thermal conductivity, electrical conductivity, and TE thermopower of the different compounds were measured in the range from 300 K through 1000 K. We observed a remarkable reduction in thermal conductivity as a result of increasing the CaO planar density for the Nb-doped RP compounds, from a value of 2.9 W m−1 K−1 for m = ∞ down to 1.3 W m−1 K−1 for m = 1 at 1000 K. This trend was, however, accompanied by a corresponding reduction in electrical conductivity from 76 Ω−1 cm−1 to 2.9 Ω−1 cm−1, which is associated with electron scattering. Finally, we propose an approach that enables optimization of the TE performance of these RP compounds.

鉄鋼材料における潤滑油中の低摩擦係数化に及ぼす高密度格子欠陥の影響

鉄鋼材料における潤滑油中の低摩擦係数化に及ぼす高密度格子欠陥の影響

Lattice-matched magnetic tunnel junctions using a Heusler alloy Co2FeAl and a cation-disorder spinel Mg-Al-O barrier

Perfectly lattice-matched magnetic tunnel junctions (MTJs) consisting of a Heusler alloy B2-Co2FeAl (CFA) electrode and a cation-disorder spinel (Mg-Al-O) barrier were fabricated by sputtering and plasma oxidation. We achieved a large tunnel magnetoresistance (TMR) ratio of 228% at room temperature (RT) (398% at 5 K) for the epitaxial CFA/MgAl-O/CoFe(001) MTJ, in which the effect of lattice defects on TMR ratios is excluded. With inserting a ultrathin (≤1.5 nm) CoFe layer between the CFA and Mg-Al-O, the TMR ratio further increased up to 280% at RT (453% at 5 K), which reflected the importance of controlling barrier-electrode interface states other than the lattice matching.

Effect of lattice defects on thermal conductivity of Ti-doped, Y2O3-stabilized ZrO2

The evolution of lattice structure and thermal conductivity has been studied systematically for a range of Ti-doped, Y2O3-stabilized ZrO2 (YSZ) solid solutions. The mechanism of reducing the thermal conductivity by Ti doping has been determined. Ti4+ mainly substitutes for Zr4+ below a critical composition factor (x⩽0.08), above which the interstitial Ti4+ need to be considered separately. The effect of lattice defects caused by mass and radius differences between Ti4+ and Zr4+ ions on the phonon scattering coefficient was discussed quantitatively. And the reduction of oxygen vacancy by interstitial Ti4+ ions which increases the thermal conductivity at high Ti doping content was also determined. Concerning the integrated phase stability and thermo-mechanical properties, Ti-doped YSZ is believed to be a promising candidate for thermal barrier coatings at higher temperature.

Computational study of lattice defects in metal–hydrogen systems

Abstract Effects of lattice defects in vanadium hydrides on hydrogen storage property were analyzed by computer simulation. Element substitution, dislocation, and polyhedral surface were modeled as for point, line and plane lattice defects. DFT calculation revealed that Mo-substitution in β-phase vanadium hydride enhanced the shift of hydrogen occupancy from O Z1 site to neighboring T sites. Classical MD calculation on edge dislocation in a-phase vanadium hydride showed that interaction between edge dislocations was reduced by hydrogen aggregation at the vicinity of dislocation core. The MD simulation on polyhedral vanadium nanoparticle showed that polycrystal structure with fivefold symmetry can be generated by hydrogenation as a result of multi-twin-boundaries associated with bcc to bct transformation. Structure models of lattice defects were also briefly discussed.