Increasing Li Content Research Articles

Promising fuels for energetics: Spherical Al-Li powders with high reactivity via incorporation of Li

To improve the heat release and reactivity of Al, Li was incorporated into Al via the centrifugal atomization in this study for obtaining Al-Li alloy powders. The microstructure and composition of the samples were characterized by SEM, XRD, and ICP. The oxidation kinetics were evaluated via TG/DSC, and the energetic performance of the Al-Li/KP composites was tested. The results show that spherical Al-Li alloy powders with the well-distributed dendritic structure are obtained that are mainly composed of αAl and Al-Li compounds. The oxidization rate of Al-Li alloy powders is higher than pure Al, owing to the decreasing activation energy caused by the catalysis of the soluble Li in Al and Al-Li compounds. The shorter ignition delay and higher reaction rate of Al-Li/KP with increasing Li content in Al-Li alloy powders is a result of the microexplosion of Al-Li. Therefore, Al-Li alloy powders with high reactivity are promising fuels for energetic materials.

Effects of Li content on microstructure and mechanical properties of as-cast Mg−xLi−3Al−2Zn−0.5Y alloys

The effects of Li content on the microstructure and mechanical properties of the as-cast Mg−xLi−3Al−2Zn− 0.5Y (LAZx32-0.5Y) alloys were investigated by XRD, SEM, TEM, hardness tester and universal testing machine. The results show that the matrix of the alloy transforms from α-Mg to α-Mg+β-Li and then to β-Li when the Li content increases from 4% to 14% (mass fraction). All LAZx32-0.5Y alloys contain AlLi and Al2Y, while MgLi2Al appears only in the alloy containing the β-Li matrix. As the Li content increases, the content of AlLi and MgLi2Al gradually increases, while the content of Al2Y does not change much. As the Li content increases from 4% to 10%, the ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually decrease while the elongation gradually increases. The corresponding fracture mechanism changes from cleavage fracture to quasi-cleavage fracture and then to microporous aggregation fracture. This is mainly attributed to the decrease of α-Mg and the increase of β-Li in the alloy. When the Li content continues to increase to 10% and 14%, the yield strength, ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually increase, while the elongation decreases sharply, which is mainly attributed to the nano-scale MgLi2Al uniformly distributed in the β-Li matrix.

Catalytic Performance of Li/Mg Composites for the Synthesis of Glycerol Carbonate from Glycerol and Dimethyl Carbonate.

A series of Li/Mg composites were synthesized by the coprecipitation method using magnesium and lithium nitrates, and then used for the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate (DMC). The experimental results indicated that Li/Mg composites were prospective catalysts for GC synthesis. 92.05% glycerol conversion and 90.61% GC yield were obtained after reacting at 80 °C for 2 h in the presence of Li/Mg composites. The structure and properties of Li/Mg composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller (BET), and CO2–temperature-programmed desorption (TPD) techniques. It was inferred that the basic strength and basicity of Li/Mg composites were improved with increase in Li content. It was concluded that Li2CO3 was the main reactive species. A too-strong basic strength of Li/Mg composites could facilitate the glycerol conversion but impair GC selectivity.

Impact of Li concentration in KMgF3:Eu,Yb fluoroperovskite on structure and luminescence properties

In this work, europium, ytterbium, and lithium doped fluoroperovskite type-KMgF3 (KMgF3:Eu,Yb,Li) was synthesized using the sol-gel method. The structural and luminescence properties of KMgF3:Eu,Yb,Li compound were investigated by radioluminescence, thermoluminescence (TL), and optically stimulated luminescence (OSL) methods. Different contents of the alkali metal lithium (Li) co-dopant have been studied regarding the influence on the structure and luminescence properties. The structures of the samples were studied using the x-ray diffraction (XRD) method. We found cubic-KMgF3 (Parascandolaite) and tetragonal-MgF2 phases for all produced samples. Additional Eu, Yb doping, and Li co-doping resulted in the formation of hexagonal-Li2O2 and cubic-MgO phases while reducing the MgF2 phase in KMgF3 dispersions that were confirmed with XRD and Rietveld refinement analyses. Moreover, the lattice parameters of KMgF3 were calculated for the undoped and Li co-doped samples. Scanning electron microscope images revealed increased crystalline formations with increasing Li concentration in the structure. Fourier transform infrared spectroscopy indicated a reduction of Mg-F bands for all samples due to Mg+2 ion substitutions with Eu, Yb doping, and Li co-doping. It was observed that the intensity of the TL peaks in the TL glow curves appeared as the Li concentration increased without shifting the peak positions as a function of temperature. The OSL curves of KMgF3:Eu,Yb,Li decayed slowly and the luminescence intensity reached a maximum with 15 mol% Li content. The obtained results tend to suggest that the investigated Eu- and Yb-doped and Li co-doped parascandolaite polycrystals exhibit promising luminescent properties and could be considered as appropriate candidates for various technological applications including radiation dosimetry.

Inducing lattice defects in calcium ferrite anode materials for improved electrochemical performance in lithium-ion batteries

Enhancing the electrical conductivity of electrode materials via a cationic substitution strategy was recognized as an effective way of improving the electrochemical performance of Li-ion batteries. Thus, LixCa1-xFe2O4 nanoparticles were synthesized via a facile inexpensive process at low temperature. XRD peaks refer to the formation of an orthorhombic structure with the Pnma space group. HR-TEM investigations reveal orthorhombic-like shape for pure CaFe2O4, nanoplatelet-like morphology for Li0.05Ca0.95Fe2O4 and irregular distorted crystals for Li0.1Ca0.9Fe2O4. Voids and pores in Li-doped CaFe2O4 were confirmed by FESEM and BET measurements. XPS spectra of O1s prove that Li-doped CaFe2O4 have higher conductivity due to the created lattice defects and oxygen species. Li-doped CaFe2O4 anodes exhibit great improvement in their initial discharge capacities ∼1219 and 1606 mAhg−1 upon substitution of Ca with 5% and 10% Li, respectively. Furthermore, 10% Li-doped CaFe2O4 anode displays the highest Li-ions diffusion coefficient and exchange current density due to the enhanced Li+ ions mobility. Moreover, the DC activation energies for the LixCa1-xFe2O4 nanoparticles decreased with increasing Li content.

First-principles study of crystal structure prediction, electronic, thermodynamic and mechanical properties of Al-Li binary system

First-principles calculations based on density functional theory (DFT) have been used to search for the energetically stable crystal structures in the Al-Li binary system throughout all possible Al concentrations. Five ground state structures are found at Li5Al2, Li4Al2, Li3Al2, Li2Al2 and Li1Al15 compositions. The electronic, thermodynamic and mechanical properties of all these structures are systematically investigated. We analyze the formation energies, phonon spectra, and elastic tensor to confirm the energy, thermodynamic and elastic stabilities, respectively. The electronic band structures and corresponding density of states indicate the metallic nature of these structures. We also analyze the bulk modulus B, shear modulus G, Young’s modulus E, the Poisson’s ratio ν and B/G ratio as a function of the Li concentration in Al-Li binary system, and the spatial direction dependences of elastic moduli. The elastic wave velocities and Debye temperature generally increase, while the melting temperature monotonically decrease with the increasing Li concentration. The calculated results are in good agreement with the existing experimental and theoretical data. The comprehensive understanding of the material properties will be vital for practical applications of the Al-Li binary system.

Insights on the Structural Changes and Mechanical Properties of Lithiated Li1+XMn2O4 Nanoporous Structures, Where 0 ≤ x ≤ 1 for Li-Ion Battery Cathodes

Most cathode materials for Li-ion batteries suffer from severe specific capacity due to structural changes that occur during the process of cycling, which may lead to fractures. Nanoporous structured materials can act as a host lattice to accommodate Li during the processes of intercalation and de-intercalation for the application of Li-ion batteries. These materials have large surface areas and volume density which allows them to flex within their pores during cycling. Herein, molecular dynamics simulations were used to study the structural changes and mechanical properties of lithiated Li1+xMn2O4 nanoporous structures to bring insights into the development of newer applications for Li-ion batteries. The DL_POLY code under the NST ensemble was employed to recrystallize three nanoporous structures, with different lattice sizes i.e. 75 Å, 69 Å and 67 Å and varying Li concentrations. The structures evolved into single and multiple grains during the recrystallization process. The microstructures harvested from the structures resulted in defective spinel and layered components. The pores of the structures changed in size with increasing Li concentration, where they either reduce, increase or close up; this was also accompanied by volume change in materials. Consequently, the nanoporous 69 Å was observed to have better resistance to volume change at Li1.75Mn2O4 concentration which rendered its counterparts evolving into multi-grained structures and experiencing great expansion. Furthermore, at this concentration, nanoporous 69 Å showed robust properties in terms of its yield strength of 9.65 GPa, compared to nanoporous 75 Å with 2.77 GPa and 67 Å with 6.84 GPa. Nanoporous 69 Å is, therefore, more resilient to structural changes, which imply that it can better withstand harsh conditions that may lead into the cathode to fracture.

Pressure-induced superconductivity in Li-Te electrides

Electrides, which accommodate excess of electrons in lattice interstitials as anions, usually exhibit interesting properties and broad applications. Until now, most electrides, especially at high pressures, show semiconducting/insulating character arising from the strong localization of interstitial and orbital electrons. However, modulating their connectivity could turn them into metals and even superconductors. In this work, with the aid of first-principles particle swarm optimization, we have identified a series of pressure-induced Li-rich electrides in the Li-Te system, in which hollow ${\mathrm{Li}}_{n}$ polyhedra accommodate the excess of electrons. With increasing Li content, these electrides undergo an interesting structural evolution. Meanwhile, the connection type of ${\mathrm{Li}}_{n}$ polyhedra experiences transitions from vertex- or edge sharing, to face sharing, leading to a diverse distribution and connectivity of interstitial electrons. All identified electrides exhibit anionic electrons-dominated metallicity. More interestingly, ${\mathrm{Li}}_{9}\mathrm{Te}$, with the highest content of ${\mathrm{Li}}_{6}$ octahedra, is superconducting with a critical temperature $({T}_{\mathrm{c}})$ of 10.2 K at 75 GPa, which is much higher than typical electrides (e.g., $12\mathrm{CaO}\ifmmode\cdot\else\textperiodcentered\fi{}7{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, ${\mathrm{Ca}}_{2}\mathrm{N}$, and ${\mathrm{Y}}_{2}\mathrm{C}$). Its superconductivity mainly originates from the coupling between hybridized electrons (anionic and atomic non-$s$-state ones) and Te-dominated phonons.

Chemiresistors Based on Li-Doped CuO–TiO2 Films

Chemiresistors based on thin films of the Li-doped CuO–TiO2 heterojunctions were synthesized by a 2-step method: (i) repeated ion beam sputtering of the building elements (on the Si substrates and multisensor platforms); and (ii) thermal annealing in flowing air. The structure and composition of the films were analyzed by several methods: Rutherford Backscattering (RBS), Neutron Depth Profiling (NDP), Secondary Ion Mass Spectrometry (SIMS), and Atomic Force Microscopy (AFM), and their sensitivity to gaseous analytes was evaluated using a specific lab-made device operating in a continuous gas flow mode. The obtained results showed that the Li doping significantly increased the sensitivity of the sensors to oxidizing gases, such as NO2, O3, and Cl2, but not to reducing H2. The sensing response of the CuO–TiO2–Li chemiresistors improved with increasing Li content. For the best sensors with about 15% Li atoms, the detection limits were as follows: NO2 → 0.5 ppm, O3 → 10 ppb, and Cl2 → 0.1 ppm. The Li-doped sensors showed excellent sensing performance at a lower operating temperature (200 °C); however, even though their response time was only a few minutes, their recovery was slow (up to a few hours) and incomplete.

Magnesium Diffusion from MgO Substrates in Sol–Gel‐Derived NiO Epitaxial Films: Effects of Heat Treatment Temperature and Li Doping

The effects of heat treatment temperature and Li doping on the structural properties of sol–gel‐derived NiO epitaxial films on MgO (100) substrates are investigated. X‐ray diffraction measurements indicate that the out‐of‐plane lattice parameters of undoped NiO films increase as the heat treatment temperature increases. This increase is particularly significant in films treated above 900 °C, in which out‐of‐plane and in‐plane lattice parameters are larger than the expected values for bulk NiO. This result cannot be explained by the strain originating in the lattice mismatch between NiO and MgO. In addition, the bandgap drastically increases in undoped films treated above 900 °C. Secondary ion mass spectrometry depth profiling demonstrates that undoped films treated above 900 °C are Ni1−xMgxO alloys generated by the diffusion of Mg from MgO substrates into NiO films, resulting in the anomalous characteristics of the prepared films. Furthermore, it indicates that the diffusion of Mg is reduced in Li‐doped films, which can be explained on the basis of defect chemistry, in which Ni vacancies decrease with the increase in Li concentration. Consequently, the increases in the lattice parameter and bandgap at high heat treatment temperatures are reduced in Li‐doped films.

Structural, optical and electrical properties of CuSCN nano-powders doped with Li for optoelectronic applications

Pure and Li-doped CuSCN nano-powders were prepared using an in situ method. Structural, optical and electrical properties of the prepared samples were investigated using X-ray diffraction (XRD), UV–Visible spectrophotometer and simple electrical circuit. XRD measurements showed that all pure and doped samples with 1%–7% Li have the hexagonal structures. The crystallite size of CuSCN decreased from 39.46 nm to 36.42 nm with increasing Li concentration from 0 to 7%. The values of direct and indirect optical band gap energies of pure and Li-doped CuSCN nano-powders were calculated. Direct optical band gap energy increased from 3.60 eV to 4.20 eV and indirect optical band gap energy increased from 2.36 eV to 3.20 eV by doping CuSCN with Li. The dc electrical conductivity was calculated at room temperature for all prepared CuSCN samples. Electrical conductivity decreased from 6.04 × 10−8 (Ω.cm)−1 to 2.82 × 10−8 (Ω.cm)−1 with increasing Li concentration from 0 to 7%. The optoelectronic performance of CuSCN was improved by doping with Li. As a result, Li-doped CuSCN could be a good candidate material as a window layer and as a hole transport layer (HTL) for producing more efficient solar cells.

Stepwise Li Substitution Induced Structure Evolution and Improved Nonlinear Optical Performance for Diamond-like Sulfides.

One of the key scientific issues for exploration of novel infrared nonlinear optical (NLO) crystals is to obtain ones with good hybrid NLO behaviors. Herein, we report four diamond-like Ag-based sulfides via stepwise Li substitution of Ag in Ag2ZnSnS4, including Ag2ZnSnS4 (1), (Li1.22Ag0.78)ZnSnS4 (2), (Li1.58Ag0.42)ZnSnS4 (3), and Li2ZnSnS4 (4). With the increase of Li content, the sulfide's noncentrosymmetric crystal structure changes from tetragonal I42m for 1, to orthorhombic Pmn21 for 2 and 3, and to monoclinic Pn for 4. Accordingly, their NLO responses are improved along with the increase of Li content, viz. from non-NLO-active for 1, to non-phase-matchable for 2 and 3, and to phase-matchable for 4. Their optical band gaps also increase regularly. The relationship between their chemical compositions, crystal structures, and NLO activities is investigated by means of chemical structural analysis and theoretical calculation. This work offers a new systematic case for designing promising NLO-active compounds via rarely adopted cation's stepwise partial substitution and understanding the chemical composition-structure-NLO property relationship.

D0 ferromagnetism in Li‐doped ZnO compounds

Recently, d0 ferromagnetic materials have been projected as one of the promising novel materials for spintronics applications. In this work, we have studied Li-doped ZnO compounds, i.e. Zn1-xLixO (x=0, 0.02, 0.04, and 0.06) samples, prepared by the solid-state reaction route method. From the study of crystal structure using X-ray diffraction (XRD) patterns, it is evident that the prepared materials have been formed in a single-phase of the hexagonal wurtzite structure. The refinement of the XRD patterns suggests that there are very small changes in the lattice parameters upon Li-incorporation in ZnO. The average crystallite size (SC), estimated from XRD patterns was found to be in the range of 35-50 nm. The microstructural study by scanning electron microscope reveals the uniform morphology of the grains of the order of 50-70 nm. The energy dispersive spectrum indicates that no unwanted ferromagnetic impurities have crept into the final prepared samples. The measurement of the temperature (T) variation of magnetization (M) with SQUID magnetometer indicates that undoped ZnO exhibits diamagnetic property but all Li-doped compounds exhibit room-temperature ferromagnetism and with a magnetic irreversibility behavior between zero-field cooled and field cooled M-T data. From the magnetization versus field measurements at 3 and 300 K, it is observed that Li-doped samples exhibit ferromagnetic loops with ultra-soft coercivity (~50 Oe) and with a maximum saturation magnetization of 0.10 emu/gm for x= 0.02 sample, which decreases with the increase in Li concentration.

Correlation between the structure and dielectric constant of Bi0.5(Na1‐xLix)0.5TiO3 (0 ≤ x ≤ 0.20) solid solutions

AbstractBismuth sodium titanate Bi0.5Na0.5TiO3 (BNT) is a lead‐free piezoelectric ceramic material with high Curie temperature. The effect of substitution of the smaller ion Li+ for the larger ion Na+ in Bi0.5(Na1‐xLix)0.5TiO3 (0 ≤ x ≤ 0.20) on the structure of BNT is studied using powder X‐ray diffraction (XRD) and Raman spectroscopy. The Rietveld refinement analysis of the powder XRD patterns showed that all the compositions formed under the monoclinic Cc space group, with the lattice parameters showing minor changes above x > 0.08. Raman spectral parameters such as position and intensity of a peak also showed a similar trend in the same Li concentration range with increasing Li content. A corresponding change in the variation of the dielectric constant with increasing Li content is also observed, suggesting a close correlation between the crystal structure and dielectric properties of the different compositions in the Bi0.5(Na1‐xLix)0.5TiO3 solid solution series.

Effect of Cu Incorporation on Structure, Densification and Magnetic Properties of Polycrystalline Li<sub><i>x</i></sub>Ni<sub>0.2</sub>Zn<sub>0.8-2<i>x</i></sub>Fe<sub>2+<i>x</i></sub>O<sub>4</sub> Ceramics

The polycrystalline LixNi0.2Zn0.8-2xFex+2O4 and LixNi0.1Cu0.1Zn0.8-2xFex+2O4 (x = 0.0, 0.1, 0.2, and 0.3) ferrites were synthesized by the standard solid-state reaction method. The compound was sintered at 1150˚C for 5 hours. The effect of Cu substitution and its impact on the crystal structure, microstructure, complex initial permeability and magnetization of the Ni-Zn ferrites were studied. The effect of Li+ incorporation on the properties mentioned above was also investigated. X-ray diffraction patterns of the samples indicated a single cubic spinel structure for both the compound. No effect of Cu addition on crystal structure was observed. The density of the ferrites was found to be enhanced because of adding Li whereas the porosity of the samples decreased with the content of Li ions. The average value of grain size increased with the addition of Li content. The samples having Cu ions formed bigger size grains. Frequency-dependent complex initial permeability, loss tangent, and relative quality factor were studied at room temperature using an Impedance analyzer in the range of 100 Hz - 120 MHz regions. In the low-frequency region, the prepared samples exhibited a high value of permeability and after a certain frequency, the permeability falls. The value of permeability enhanced with the increase in Li whereas loss tangent was found to be reduced. The relative quality factor graphs described that the compound has excellent frequency stability up to a certain frequency which is suitable to be used in inductors, resistors, capacitors, etc. Initial permeability for LixNi0.1Cu0.1Zn0.8-2xFex+2O4 ferrites was found high than LixNi0.2Zn0.8-2xFex+2O4 which might be attributed to having bigger size grains of Cu containing samples because of easy movement of domain wall in bigger size grains. The values of saturation magnetization (Ms) were calculated for both compounds from M-H hysteresis loops and it enhanced with the increase in Li content which might be related to the modification of predominant exchange interactions between the cations. The Cu-containing compound exhibited higher values of saturation magnetization. The cation distribution reflects this increment because ferromagnetic Ni2+ and paramagnetic Cu2+ ions occupied in the B-sites and the diamagnetic Zn and paramagnetic Li occupied in the A-sites; therefore, net magnetic moments increased gradually. The studied materials might be used as an alternative to Pb-based compounds and would be environment friendly.

The effect of major constituents on microstructure and mechanical properties of cast Al-Li-Cu-Zr alloy

The effect of major constituents (the Li content increases from 0.5 to 3 wt% and the Cu content decreases from 4.5 to 2 wt%) on microstructure and mechanical properties of cast Al-Li-Cu-Zr alloy were studied to understand a qualitative assessment of sequence and kinetics of multiple precipitations. Increasing the Li content progressively raises the melting temperature from 520 °C in 1# alloy (Al-0.5Li-4.5Cu, wt%) and 2# alloy (Al-1Li-4.5Cu) to 560 °C in 6# alloy (Al-3Li-2Cu). In addition, the variations of the major constituents result in the changes of the type and volume fraction of the inter- and intra-granular intermetallic phases. TEM results indicate that minor modifications to alloy composition greatly alter precipitation behavior during isothermal aging. The Li-poor alloy (2# alloy) presents a much shorter incubation time of T1-Al2CuLi precipitate than the Li-rich alloy (Al-1.5Li-4.5Cu, 3# alloy), while the nucleation of θ'-Al2Cu precipitate is promoted in Li-rich alloy. No typical spherical δ'-Al3Li precipitate is observed in 2# and 3# alloys during isothermal aging, except for the as-quenched 3# alloy. The preferential nucleation of δ' precipitate on the coherent and broad face of θ' precipitate is observed in 2# and 3# alloys, leading to the formation of “sandwich-like” δ'/θ'/δ' phases. Further decreasing Cu content to 2 wt% and increasing Li content to 3 wt% (6# alloy), the predominant phase in the matrix is δ' precipitate, accompanied by a small amount of unevenly distributed θ' and T1 precipitates. The best balance between ductility and strength is obtained by 2# alloy aged for 32 h, but 6# alloy has significant advantages in terms of density (2.437 g/cm3) and elastic modulus (82.65 GPa) over 2# alloy (density: 2.675 g/cm3; elastic modulus: 75.45 GPa).

Closing the gap between theory and experiment for lithium manganese oxide spinels using a high-dimensional neural network potential

Many positive electrode materials in lithium ion batteries include transition metals which are difficult to describe by electronic structure methods like density functional theory (DFT) due to the presence of multiple oxidation states. A prominent example is the lithium manganese oxide spinel Li$_x$Mn$_2$O$_4$ with $0\leq x\leq2$. While DFT, employing the local hybrid functional PBE0r, provides a reliable description, the need for extended computer simulations of large structural models remains a significant challenge. Here, we close this gap by constructing a DFT-based high-dimensional neural network potential (HDNNP) providing accurate energies and forces at a fraction of the computational costs. As different oxidation states and the resulting Jahn-Teller distortions represent a new level of complexity for HDNNPs, the potential is carefully validated by performing X-ray diffraction experiments. We demonstrate that the HDNNP provides atomic level details and is able to predict a series of properties like the lattice parameters and expansion with increasing Li content or temperature, the orthorhombic to cubic transition, the lithium diffusion barrier, and the phonon frequencies. We show that for understanding these properties access to large time and length scales as enabled by the HDNNP is essential to close the gap between theory and experiment.

Concentration of lithium by forward osmosis

As an applying potential for a part of production of lithium (Li) from salt lake brine, forward osmosis was investigated by using semi-permeable membranes, sodium chloride (NaCl) and magnesium chloride (MgCl2) as draw solutions under several operational conditions. Cellulose triacetate and thin-film composite membranes and their orientations were compared. The results indicated that concentration of Li was higher using the thin-film composite membrane with MgCl2 as the draw solution. The effect of pH was insignificant. The results also showed that water flux decreased with increasing Li concentration on the feed side. Internal concentration polarization played an important role when rejection of Li was higher in the active layer facing feed solution system.

Ionic conductivity in LixTaOy thin films grown by atomic layer deposition

The material system Li-Ta-O is a promising candidate for thin-film solid-state electrolytes in Li-ion batteries. In the present study, we have varied the Li content x in LixTaOy thin films grown by atomic layer deposition (ALD) with the aim of improving the Li-ion conductivity. The amorphous films were grown at 225 °C on insulating sapphire and on conductive Ti substrates using tantalum ethoxide (Ta(OEt)5), lithium tert-butoxide (LiOtBu) and water as reactants. The film composition was determined by time-of-flight elastic recoil detection analysis (TOF-ERDA), displaying an almost linear relationship between the pulsed and deposited Li content. The ionic conductivities were determined by in-plane and cross-plane AC measurements, exhibiting an Arrhenius-type behaviour and comparatively weak thickness-dependence. Increasing Li content x from 0.32 to 0.98 increases the film conductivity by two orders of magnitude while higher Li content x = 1.73 results in decreased conductivity. A room-temperature conductivity σRT of ~10−8 S cm−1 is obtained for a 169 nm thick Li0.98TaOy film. The evolution of conductivity and activation energy suggests a competing effect between the concentration and the mobility of mobile Li ions when more Li are incorporated. The compositional dependence of Li transport mechanism is discussed.

Electrical Conductivity Studies in Sol–Gel‐Derived Li‐Doped NiO Epitaxial Thin Films

The electrical properties of transparent Li‐doped nickel oxide (NiO) epitaxial thin films grown on MgO (100) substrates using a sol–gel spin‐coating technique are investigated as to the Li concentration as determined by secondary ion mass spectroscopy. The epitaxial growth of the cubic Li‐doped NiO films with a cube‐on‐cube relationship is confirmed by X‐ray diffraction measurements. The electrical conductivity increases superlinearly with increasing Li concentration from 0.028 to 7.5 at%. The temperature dependence of the conductivity and the linear dependence of the activation energy on the mean distance between Li ions suggest that the conductivity can be explained within a hopping conduction framework. However, the significant Hall voltages observed in Hall effect measurements suggest the existence of nonhopping carriers in addition to hopping carriers. The Li concentration dependence of the conductivity cannot be well explained by the widely used model of small polaron hopping in which small polarons conduct through thermally activated hopping between nearest‐neighbor Ni sites. Instead, the observed dependence is well explained quantitatively by a model combining polaronic interacceptor hopping and nonhopping conductions. Polaronic interacceptor hopping conduction dominates for Li concentrations below 1 at%, whereas nonhopping conduction dominates for higher Li concentrations.