Activation Energy For Migration Research Articles

Measurement of Bulk Oxygen Diffusivity in (La0.8Sr0.2)0.95MnO3±δ

Strontium-doped lanthanum manganite is widely used as a cathode material for solid oxide fuel cells (SOFCs). In this study, the oxygen diffusivity in A-site-deficient (La0.8Sr0.2)0.95MnO3±δ (LSM-20) was measured as a function of temperature (600°C, 700°C, and 800°C) and oxygen partial pressure (0.03 atm, 0.16 atm, and 0.30 atm). Tracer (O-18) concentration profiles were measured in single-crystal epitaxial thin films of LSM-20 by time-of-flight secondary-ion mass spectroscopy (TOF-SIMS). The profile was fit to a diffusion equation to obtain the diffusivity of oxygen in bulk LSM-20 as a function of temperature and oxygen partial pressure. A defect model was used in conjunction with the experimental data to calculate the activation energies of oxygen migration, Schottky reaction, redox reaction, and charge disproportionation reaction in LSM-20. These calculated data were then used to calculate the Brouwer diagram of (La0.8Sr0.2)0.95MnO3±δ at 800°C, a typical operating temperature of SOFCs.

Electrodiffusion of alkali ions in alkali niobophosphate glasses and glass‐forming melts

AbstractElectrical conductivity of Li(Na,K)2O‐Nb2O5‐P2O5 glasses and glass‐forming melts has been measured in a wide temperature range (298‐1173 K). Logarithm of the preexponential factor and activation energy of migration have been determined. Mixed alkali effect has been observed in niobophosphate glass‐forming melts. Diffusion coefficients for Li+, Na+, and K+ ions have been calculated. The influence of the type of alkali ion and Nb2O5 content on the diffusion coefficients has been determined.

Na+ ion migration on the surface of reduced graphene oxide

The increasing demand of sodium ion batteries (SIBs) remarkably accelerates the study of solid-state sodium ion conductors due to their potential application as solid-state electrolytes in SIBs. In the present work, the sodium ion is attached to reduced graphene oxide (rGO) to realize a sodium ion conductor. Tuning the activation energy of migration for Na+ and Li+ ions on rGO surface is investigated by varying the concentration of both ions. The lowest values of activation energies for Na+ and Li+ conduction are found to be 0.28 eV and 0.37 eV, respectively. It is seen that the activation energy of migration of the Na+ ion is smaller than that of the Li+ ion. The lower positive charge density of Na+ compared to Li+ causes this lowering of activation energy in Na+ due to the comparatively weak cation–π interaction between the Na+ ion and the carbon hexagon. From the relaxation study, the relaxation exponent (β) value of the Na+ ion is found to be smaller than that of the Li+ ion. This deviation from Debye-type relaxation behavior of the Na+ ion also agrees well with the decreasing value of activation energy as mentioned above. We hope that this study will aid the design of ion conductors for solid-state SIBs.

Li+ transport channel size governing Li+ migration in garnet-based all-solid-state lithium batteries

Li+ transport channel size of garnet-type Li7La3Z2O12 (LLZO) solid electrolytes is continuously regulated to study its governing of Li+ migration in application of all-solid-state batteries. Results show that the Li+ migration activation energy decrease with the decrease of Li+ transport channel size and then increase with further decrease of Li+ transport channel size. With Li+ transport channel size of 12.954 Å, the Li+ migration activation energy reaches minimum of 0.28 eV. The cyclic voltammogram of Au/Li7La3-XCaXZr2-YTaYO12/Li cells show that, with Li+ transport channel size of 12.954 Å, the redox peaks is at ±0.23 V, which is more symmetrical and closer to 0 V compared to both larger and smaller Li+ transport channel size of 12.961 Å (0.38 V and −0.32 V) and 12.935 Å (0.50 V and −0.40 V). This suggests that LLZO with Li+ transport channel size of 12.954 Å has better charge-discharge reversibility of lithium deposition and dissolution and less energy consumption when used as solid electrolyte in all-solid-state lithium batteries.

Observation of the Recrystallization Process in Pure Nb and Zr Using Positron Lifetime Spectroscopy and XRD Techniques

Results of research on the recrystallization of highly deformed Nb and Zr with the use of positron lifetime spectroscopy and XRD measurements are presented here. A significant decrease in positron lifetime during annealing of deformed Nb and Zr samples is observed, which is clearly correlated with changes in the pole figures and reduction of the crystal lattice strain of the tested samples. This indicates their recrystallization, that is, nucleation and growth of new, defect free grains. Application of the positron diffusion trapping model to description of the obtained dependencies allows us to determine the activation energy of migration of grain boundary in both metals, which is 2.26 ± 0.4 eV and 1.33 ± 0.6 eV for Nb and Zr, respectively.

Strain tunable ionic transport properties and electrochemical window of Li10GeP2S12 superionic conductor

The sulfide solid electrolytes with high ionic conductivity at room temperature may become a potential candidate of solid electrolyte in all-solid-state lithium batteries. However, they have a lower intrinsic redox stability against inert electrodes, and generally unstable against lithium metal anode. Here, using density functional theory calculations we show that the ionic transport and band gap can be optimized by adjusting the mechanical strain on sulfide solid electrolyte Li10GeP2S12(LGPS). Our theoretical results demonstrate that the tensile strain strongly influences the electronic structure and ion channel in LGPS materials, which results in wider band gap and higher lithium ionic conductivity. LGPS crystal can be stretched 15% along c direction without breakage due to its good ductibility. For the LGPS with a strain parallel to c direction, its band gap continuously increases to its maximum width of 4.16 eV as the strain increases up to 12%. In addition, the activation energies for lithium ion migration have been decreased by applying uniaxial strain to lattice with the aid of first principles and molecular dynamics calculations. Significantly, the lithium ion diffusion behavior will transform from one-dimensional into three-dimensional with lower activation energy in the as strained LGPS. The present study enriches the understanding of solid electrolytes and provides a framework for the future design or optimization of high-performance solid electrode.

Effect of temperature and frequency on electrical properties of composite multiferroic of lead titanate and strontium hexaferrite (PbTiO3 – SrFe12O19)

The work describes the use of dielectric and ac complex impedance and modulus spectroscopy techniques to obtain the electrical parameters like electrical conductivity and activation energy of composite multiferroic having composition (x) PbTiO3 – (1-x) SrFe12O19; where x = 0.10, 0.30, 0.50 in the frequency range 10–1000 KHz over a temperature range of 30–550 °C. The coexistence of low dielectric constant region with high dielectric constant region results in Maxwell – Wagner (M-W) polarization in the composite. Complex impedance and modulus spectroscopic analysis indicated the presence of non-Debye type dielectric relaxation in the composites. The grain (Rg) and space charge polarization resistance (RSCP) decreases with increase in temperature providing convincing evidence that the electrical properties of composite are temperature as well as microstructure dependent. The ac conductivity of composite calculated from dielectric loss and it shows an increase with increasing temperature suggesting semiconductor behavior. The hopping rate and concentration of charge carriers was calculated using Almond and West formalism based on Jonscher's universal power law. The activation energy of the ion migration and conduction was determined from temperature dependence of the hopping rate and dc conductivity respectively. For all compositions, the activation energy of dc conductivity is greater than that of hopping; i.e., Ea > Em. The increase in drift mobility represents enhanced mobility of the charge carriers due to thermal activation.

Transition from thermally assisted to mechanically driven boundary migration and related apparent activation energies

Grain boundary migration during deformation of nanostructured materials has been reported for a variety of materials and loading conditions. As boundary migration occurs even under cryogenic conditions, it is believed to be mainly mechanically driven, although results suggest thermal assistance. Yet, these contributions could not be separated and the underlying apparent activation energies remain uncertain. Here we present an approach that is capable to determine the average activation energies for mechanically driven boundary migration. While the apparent activation energy is increasing with temperature, below critical temperatures it becomes zero, indicating the existence of an entirely mechanically driven regime.

Defects, Dopants and Lithium Mobility in Li9V3(P2O7)3(PO4)2

Layered Li9V3(P2O7)3(PO4)2 has attracted considerable interest as a novel cathode material for potential use in rechargeable lithium batteries. The defect chemistry, doping behavior and lithium diffusion paths in Li9V3(P2O7)3(PO4)2 are investigated using atomistic scale simulations. Here we show that the activation energy for Li migration via the vacancy mechanism is 0.72 eV along the c-axis. Additionally, the most favourable intrinsic defect type is Li Frenkel (0.44 eV/defect) ensuring the formation of Li vacancies that are required for Li diffusion via the vacancy mechanism. The only other intrinsic defect mechanism that is close in energy is the formation of anti-site defect, in which Li and V ions exchange their positions (1.02 eV/defect) and this can play a role at higher temperatures. Considering the solution of tetravalent dopants it is calculated that they require considerable solution energies, however, the solution of GeO2 will reduce the activation energy of migration to 0.66 eV.

Core-Shell Nanocomposites for Improving the Structural Stability of Li-Rich Layered Oxide Cathode Materials for Li-Ion Batteries.

The structural stability of Li-rich layered oxide cathode materials is the ultimate frontier to allow the full development of these family of electrode materials. Here, first-principles calculations coupled with cluster expansion are presented to investigate the electrochemical activity of phase-separation, core-shell-structured xLi2MnO3·(1 - x)LiNiCoMnO2 nanocomposites. The detrimental surface effects of the core region can be countered by the Li2MnO3 shell, which stabilizes the nanocomposites. The operational voltage windows are accurately determined to avoid the electrochemical activation of the shell and the subsequent structural evolution. In particular, the dependence of the activation voltage with the shell thickness shows that relatively high voltages can still be obtained to meet the energy density needs of Li-ion battery applications. Finally, activation energies of Li migration at the core-shell interface must also be analyzed carefully to avoid the outbreak of a phase transformation, thus making the nanocomposites suitable from a structural viewpoint.

Cations size mismatch versus bonding characteristics: synthesis, structure and oxygen ion conducting properties of pyrochlore-type lanthanide hafnates

This work describes the synthesis, structural characterization and electrical properties of solid solutions with the general formula Gd2Hf2−xBxO7, where B = Ti4+, Sn4+ and Zr4+. All samples were successfully prepared in ~ 30 h, via a mechanochemical reaction in a planetary ball mill, using the corresponding elemental oxides as starting chemicals. The XRD and Raman spectroscopy analysis of the title samples revealed that on firing at 1500 °C Hf4+ substitution by Sn4+ and Ti4+ produces better ordered pyrochlore structures and decreases the electrical conductivity of Gd2Hf2O7 by more than two orders of magnitude (from 2.7 × 10−4 at 700 °C to 8.71 × 10−7 and 1.12 × 10−6 Sm cm−1, for Gd2Sn2O7 and Gd2Ti2O7, respectively). By contrast, the Gd2Hf2−xZrxO7 system remains disordered with conductivity increasing by almost an order of magnitude and reaching a value for Gd2Zr2O7 of 1.55 × 10−3 Sm cm−1 at 700 °C, whereas the activation energy for oxygen migration decreases in both, the Sn- and Ti-containing systems, and increases slightly in the Zr-containing solid solution. These changes cannot be only explained when taking into account the cations size ratio criteria; the covalency of the metal bond plays also a key role in determining the structural characteristics and electrical properties of the title three systems.

Verification of Strain-Induced Fast Ionic Conduction in Thin-Film Electrolyte Via Experimental and Computational Study

Epitaxial strain engineering in nanostructured oxides has attracted great attention to various energy storage and conversion devices requiring fast ionic conduction, such as solid-oxide fuel cells (SOFCs), catalytic membranes, and electrochemical sensors. Recently, remarkable enhancement of ionic conductivity has been achieved by the epitaxial strain in ultra-thin epitaxial and multi-layered films.1-3 However, the strain engineering still has some lack of understanding of how much enhancement can be achieved by strain, and how to maximize the strain in nanostructured oxides. Herein, for the reliable and effective strain engineering for fast ionic conduction, strain effect on oxygen ion conductivity of thin films (Gd0.2Ce0.8O1.9-δ (100) : GDC) was investigated through both experimental study and density functional theory (DFT) calculations. We measured the oxygen ion conductivity of GDC films grown in island growth mode on Nb-doped SrTiO3 (STO) substrate. According to the conductivity measurement via electrochemical impedance spectroscopy (EIS), the activation energy for oxygen ion migration in out-of-plane direction was reduced with increase of film thickness. Furthermore, through careful strain analysis using high-resolution X-ray diffraction (HR-XRD) and strain mapping in transmission electron microscopy (TEM), the intrinsic tensile strain along column boundaries (CB) was found to be more predominant than the epitaxial strain formed at the film-substrate interface, thereby more strong tensile strain was observed in a thicker film having higher CB density. This general tendency of the activation energy change with respect to tensile strain was also verified by atomic-scale simulation in a highly doped CeO2 structure. To the best of our knowledge, this is the first experimental and theoretical verification to show the critical role of intrinsic strain on fast ion conduction in thin film electrolyte. From this presentation, you will get a great inspiration to the strain-induced fast ionic conduction in oxide thin films to improve the availability of various energy devices. References S. Schweiger, M. Kubicek, F. Messerschmitt, C. Murer, and J. L. M. Rupp, ACS Nano 8, 5032 (2014).S. Sanna, V. Esposito, J. W. Andreasen, J. Hjelm, W. Zhang, T. Kasama, S. B. Simonsen, M. Christensen, S. Linderoth, and N. Pryds, Nat. Mater. 14, 500 (2015)A. Fluri, D. Pergolesi, V. Roddatis, A. Wokaun, and T. Lippert, Nat. Commun. 7, 10692 (2016)

Lithium diffusion in Li5FeO4

The anti-fluorite type Li5FeO4 has attracted significant interest as a potential cathode material for Li ion batteries due to its high Li content and electrochemical performance. Atomic scale simulation techniques have been employed to study the defects and Li ion migration in Li5FeO4. The calculations suggest that the most favorable intrinsic defect type is calculated to be the cation anti-site defect, in which Li+ and Fe3+ ions exchange positions. Li Frenkel is also found to be lower in this material (0.85 eV/defect). Long range lithium diffusion paths were constructed in Li5FeO4 and it is confirmed that the lower migration paths are three dimensional with the lowest activation energy of migration at 0.45 eV. Here we show that doping by Si on the Fe site is energetically favourable and an efficient way to introduce a high concentration of lithium vacancies. The introduction of Si increases the migration energy barrier of Li in the vicinity of the dopant to 0.59 eV. Nevertheless, the introduction of Si is positive for the diffusivity as the migration energy barrier increase is lower less than that of the lithium Frenkel process, therefore the activation energy of Li diffusion.

X-ray Diffraction Investigation of Annealing Behavior of Peened Surface Deformation Layer on Precipitation Hardening Stainless Steel

In order to investigate the recrystallization behavior of peened surface deformation layer of precipitation hardening stainless steel, a classic x-ray diffraction line profile analysis, Voigt method, was carried out on peened 17-4PH with different isothermal annealing temperatures. The activation energy of domain boundary migration (Qa) and the activation energy of microstrain relaxation (Qb) were calculated by regression analysis in different annealing temperature conditions. The results show that the value of Qa decreases with annealing temperature increasing, which is due to the influence of precipitation (e-Cu) size on the movements of grain and subgrain boundaries. The maximum growth rate of e-Cu particles occurs during 400 to 500 °C interval. Compared with growth behavior of domain size, microstrain relaxation behavior is less sensitive to precipitation particle size. The effects of annealing temperature and time on dislocation density are both significant when annealing temperature is lower than 500 °C. However, the effect of annealing temperature on dislocation density becomes insignificant when annealing temperature is higher than 500 °C. 300 °C annealing temperature only leads to the microstrain relaxation but nearly cannot lead to the domain size growth even if prolonging annealing time. Microstructure enhancement effect still exists in plastic deformation layer when 300 °C annealing temperature lasts for 60 min but nearly disappears when 600 °C annealing temperature lasts for 20 min.

Lithium insertion in α′-NaV2O5: Na-pillaring effect on the structural and electrochemical properties

Electrochemically formed α′-NaV2O5 bronze is investigated here as cathode material for rechargeable lithium batteries. We show that the layered structure of this compound, with Na ions located between the V2O5 layers, allows the reversible insertion of 1 lithium/mole of bronze at an average voltage of 2.1 V vs. Li+/Li. The Li insertion-extraction mechanism in α′-LixNaV2O5 is revealed thanks to ex situ XRD and Raman spectroscopy investigations. A narrow one-phase region occurs in the 0 < x ≤ 0.2 composition range while a two-phase mechanism prevails for 0.2 < x < 1. Also, we show that 0.3 additional Li ions can be inserted according to a second solid solution domain, leading to the fully lithiated α′-Li1.3NaV2O5 material. The structure of the α′-LiNaV2O5 is isomorphic to the pristine material. It is remarkable that only limited structural changes are found in the 0 < x ≤ 1.2 lithium composition range, consisting mainly in a 7% increase in the interlayer c parameter. A high structural reversibility is evidenced, which accounts for the remarkable stable capacities achieved whatever the C rate, near 120 mAh g−1 and 60 mAh g−1 at C/10 and 1C, respectively after 60 cycles. The lithium chemical diffusion coefficient DLi, in the range 10−9 – 10−10 cm2 s−1 in the 0.03 ≤ x ≤ 1.1 composition domain, is little affected by the Li concentration. The high mobility revealed for lithium ions is also supported by BVEL analysis, while a significant activation energy for Na-ions migration ascertains their immobility in the α′-NaV2O5 lattice. These results demonstrate the interest of large interlayer 2D host lattices stabilized by pillaring species such as Na to achieve a stable cycling behavior, a facile guest cation insertion and to promote the ionic diffusion.

Analytical Modeling of Organic–Inorganic CH3NH3PbI3 Perovskite Resistive Switching and its Application for Neuromorphic Recognition

AbstractThis paper presents an analytical model of resistive switching in organic–inorganic CH3NH3PbI3 perovskite. It is interpreted that the resistive switching phenomenon is due to the formation/rupture of iodine vacancy‐based conductive filament (CF) propagating in both vertical and lateral directions. Set and reset processes are explained in the model by the evolution of the CF length and radius driven by electrical and thermal forces. The model‐based simulation results can describe the experimental results, providing an estimate of several switching parameters such as the activation energy of iodine vacancy migration and the CF diameter. Learning in a two‐transistor/one‐resistor synapse structure is demonstrated by simulations. Finally, the neuromorphic recognition of multiple patterns is demonstrated through a two‐layer neural network consisting of 5625 presynaptic neurons and four postsynaptic neurons.

A thermo-kinetic correlation for grain growth in nanocrystalline alloys

The thermo-kinetic stabilization that incorporates mixed effects of grain boundary (GB) energy and activation energy for GB migration has shown enormous advantages in describing thermal stability of nanocrystalline materials. However, its underlying physics is still unclear due to the lack of proofs that the two effects coexist and act together to impact on grain growth. In this work, a thermo-kinetic correlation is derived to bridge GB energy and activation energy in nanocrystalline alloys. Meanwhile, molecular dynamic simulations are performed to determine the two parameters in Al-based systems. The results shows that upon GB segregation, the GB energy is reduced in contrast with the increased activation energy. This analytically suggests a thermo-kinetic origin for stabilization due to GB segregation, other than pure thermodynamic or kinetic sources.

Influence of the mode of deformation on recrystallisation behaviour of titanium through experiments, mean field theory and phase field model

The influence of the mode of deformation on recrystallisation behaviour of Ti was studied by experiments and modelling. Ti samples were deformed through torsion and rolling to the same equivalent strain of 0.5. The deformed samples were annealed at different temperatures for different time durations and the recrystallisation kinetics were compared. Recrystallisation is found to be faster in the rolled samples compared to the torsion deformed samples. This is attributed to the differences in stored energy and number of nuclei per unit area in the two modes of deformation. Considering decay in stored energy during recrystallisation, the grain boundary mobility was estimated through a mean field model. The activation energy for recrystallisation obtained from experiments matched with the activation energy for grain boundary migration obtained from mobility calculation. A multi-phase field model (with mobility estimated from the mean field model as a constitutive input) was used to simulate the kinetics, microstructure and texture evolution. The recrystallisation kinetics and grain size distributions obtained from experiments matched reasonably well with the phase field simulations. The recrystallisation texture predicted through phase field simulations compares well with experiments though few additional texture components are present in simulations. This is attributed to the anisotropy in grain boundary mobility, which is not accounted for in the present study.

Regulation mechanism of bottleneck size on Li+ migration activation energy in garnet-type Li7La3Zr2O12

The garnet-type lithium ion conductor, nominal Li7La3Zr2O12 (LLZO) has received a lot of interest as they are considered usable as solid electrolytes in lithium battery. The Li+ migration bottleneck size of garnet-type Li7La3Zr2O12 (LLZO) solid electrolyte are posed significant effect on Li+ transportation property. However, the regulation mechanism of the bottleneck size on the Li+ migration activation energy is not clear. In the study, equivalent substitution of tetravalent M4+ (M4+ = Ge4+, Ti4+, Sn4+, Hf4+ and Te4+) ions on Zr site of Li7La3M0.25Zr1.75O12 is designed to regulate the bottleneck size. X-ray absorption fine structure (XAFS) is applied to detect the quantitative structural information of M-doped LLZO. Experimental and calculations results show that the M4+ substitution regulate the Li+ migration bottleneck size via changing M–O bond length. The M–O bond length increases with the increase of M4+ doping ion radius which results in the increase of the bottleneck size. However, larger bottleneck size is not necessarily favorable for Li+ migration. Ge4+ and Ti4+ doped LLZO have smaller bottleneck size than the un-doped LLZO, which is more suitable for Li+ migration (corresponds to lower Ea of 0.28 eV, 0.29 eV, respectively). This study is of great significance for obtaining optimum lithium ion migration channel size for LLZO, and the regulation mechanism is universality for crystal ion conductors.

Confined Li ion migration in the silicon-graphene complex system: An ab initio investigation

Silicon-Carbon complex systems play an important role in enhancing the performance of Si-based anode materials for Li ion batteries. In this work, the Li migration property of the Silicon-Graphene (Si-Gr) complex systems are investigated by using first-principles calculations. Especially, the effects of graphene coating on the migration of Li ions are discussed in detail. The distance between Si surface and graphene in the Si-Gr system significantly affects the lateral migration of Li ions. With the decrease of the distance from 4.715 to 3.844 Å, the energy barrier of Li ion migration also decreases from 0.115 to 0.067 eV, which are all lower than that of the case without graphene d(0.135 eV). However, smaller distance (3.586 Å) brings the high energy barrier (0.237 eV). Through AIMD calculations, it is found that the graphene coating in the Si-Gr complex system would result in the larger intercalation depths, more uniform distributions, and higher migration coefficients of Li ions. Further calculations of migration coefficients of Li ions at different temperature are used to obtained the activation energy for Li ions migration in the Si-Gr system, which is as low as 0.028 eV. This low activation energy shows that it is easy for Li ions migrating in the Si-Gr system. Our study provided the basically information to understand the migration mechanism of Li ions in Si-C system.