Synthesis and electrophysical properties of novel lithium ion conducting oxides

Novel lithium ion conducting oxides with perovskite structure have been synthesized and studied. It has been found that the La_2/3−xLi_3xTiO₃ and La_2/3−xLi_3xNb₂O₆ compounds have a perovskite structure at 1/24 < x < 1/6 and 0 < x < 3/10, respectively. The results of investigating the electrical properties of both groups of perovskites indicate a high lithium ion conductivity.     

Oxygen ion diffusion in perovskite-type oxides determined by permeation and by relaxation measurements

Oxygen ion diffusion in oxides of the perovskite-type structure was determined by two methods of measurement: i) stepwise change of temperature or oxygen partial pressure of the gaseous environment of a ceramic sample, and measurement of the relaxation of electrical conductivity or oxygen content, ii) oxygen permeation through a gas dense oxide ceramic pellet from air to argon. The experimental problems and sources of errors, calculation methods of chemical diffusion coefficients and oxide ionic conductivities from these two modes of investigation are discussed. The comparison of relaxation and permeation measurements on 10 oxides of the type A_1−aA′_aM_1−bM′_bO_3−σ (A=La, Pr, Ce; A′=Sr, Ca; M=Mn, Fe; M′=Co, Ni) show advantages of the relaxation method in relation to the experimental performance and possible errors.     

EXAFS spectroscopy of perovskite-type superconducting oxides

On the basis of the investigation of the temperature dependences of EXAFS spectra of the Ba_1?x K _x BiO₃ superconducting oxide, a model of relationship between the local crystalline and electronic structures is proposed. It is found that oxygen ions vibrate in a double-well potential and their vibrations are correlated with the local electron pair transfer. Analogous specific features are also observed in the EXAFS spectra of La_2?x Sr _x CuO₄, which gives grounds to extend the proposed model to Cu-based superconductors. The model based on the unified approach makes it possible to explain the ground antiferromagnetic state, the insulator-metal transition, and the occurrence of superconductivity upon doping of La₂CuO₄ with strontium.     

Blended lithium ion conducting polymer electrolytes based on boroxine polymers

A new series of blended polymer electrolytes based on a boroxine polymer (BP) with poly(ethylene oxide) (PEO), an ethylene oxide–propylene oxide copolymer or poly(methyl methacrylate) were prepared. Good room temperature mechanical properties were exhibited by electrolytes containing in excess of 30% PEO. Cationic transference number measurements indicated that a slight improvement in lithium ion conductivity could be achieved by using a mixture of LiCF₃SO₃ and LiN(CF₃SO₂)₂ as the electrolyte salt. Electrolytes incorporating significant proportions of BP exhibited reduced lithium–polymer electrolyte interfacial resistance.     

Doped tin oxides as potential lithium ion battery negative electrodes

Recently some work has shown that tin oxide compounds can be promising anode materials in rechargeable lithium batteries. These materials show a higher capacity compared to the graphite that is used commercially. The present studies are focused on zinc doped tin oxides as anode materials, especially on the effect of ball-milling on the anode capacity. Different ratios of ZnO and SnO₂ with different times of ball-milling have been used as active materials. The inverse spinel, Zn₂SnO₄ has been prepared by both hand-grinding and ball-milling, followed by sintering and has also been investigated as an active material. Individual ball-milling of the oxides was observed to increase capacity, co-milling was fairly neutral and ball-milling before solid state reaction was observed to have a detrimental effect. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Transparent conducting oxides for electrode applications in light emitting and absorbing devices

In both light emitting devices such as light emitting diodes (LEDs), and light absorbing devices such as solar cells (also photodetectors), which are gaining considerable interest for their energy saving and energy production capability, respectively, a compromise must be struck between the need to increase the light emitting/absorbing area/potential and the need for low series resistance of the metal contact grid. This undesirable compromise can be mitigated by using transparent conducting oxides (TCOs), which heretofore have been dominated by ITO (indium tin oxide—an In-rich alloy of indium oxide and tin oxide). Due to the expected scarcity of Indium used in ITO, efforts are underway to develop indium-free TCOs for the above-mentioned devices as well as flat panel displays. ZnO heavily doped with Ga or Al (GZO or AZO) is becoming a very attractive candidate for future generation TCOs. GZO and AZO as well as multilayer TCOs consisting of two TCO layers with a thin metal layer in between have been widely investigated for LEDs and solar cells to enhance device performance. This article succinctly reviews the latest developments in and properties of TCOs, particularly in relation to thin film transparent electrode applications for LEDs and solar cells. Pertinent critical issues and possible solutions are provided as well.     

Doped lithium nickel cobalt mixed oxides for the positive electrode in lithium ion batteries

Phase pure aluminium and magnesium doped lithium nickel cobalt mixed oxides Li(Ni,Co_0.1–0.2M_≤0.05)O₂ (M=Al, Mg) were synthesised in laboratory by a synthesis procedure adopted from H.C. Stark. Structural parameters were determined by Rietveld analysis of x-ray diffraction spectra. Electrochemical characterisation took place in three-electrode teflon cells and coin-type cells versus lithium metal. Thermal stability of cathodes without electrolyte was measured by DSC. For aluminium and magnesium doped lithium nickel cobalt mixed oxides Li(Ni,Co_0.1–0.2M_≤0.05)O₂ (M=Al, Mg) the layered structure is stabilised by both aluminium and magnesium. The lithium nickel disorder is decreased by cobalt and is nearly unaffected by aluminium. According to the Rietveld refinements, magnesium seems to reduce the lithium nickel disorder strongly, even though refinements are not totally reliable in this case. Initial capacity and reversibility in the first cycle are nearly unaffected by aluminium, but strongly inferred by magnesium. Both, aluminium and magnesium doping increase the cycling stability of lithium nickel cobalt mixed oxides. Increased thermal stability of charged electrodes without electrolyte by aluminium and magnesium doping seems to be due to limited delithiation. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Co-precipitation synthesis and characterization of multiple substituted lithium manganese oxides in lithium ion batteries

Seven electroactive compounds LiMn₂O₄, LiZn_0.1Mn_1.9O₄, LiZn_0.1Mn_1.9O_3.9F_0.1, LiNi_0.1Mn_1.9O₄, LiNi_0.1Mn_1.9O_3.9F_0.1, LiZn_0.05Ni_0.05Mn_1.9O₄ and LiZn_0.05Ni_0.05Mn_1.9O_3.9F_0.1 with spinel structure, space group Fd m, were prepared by using co-precipitation procedure carried out in water-alcohol (volume ratio 1:1) solvent using adipic acid as chelating agent. The electrochemical measurements indicated that the charge/discharge capacity of the sample prepared at 600 °C is higher than that prepared by treating at 800 °C or by microwave heating. The electrochemical properties of multi-doped samples are better than those of single and double doped samples in the Li-Mn spinel skeleton. LiZn_0.05Ni_0.05Mn_1.9O_3.9F_0.1 shows the best cycle performance and the largest capacity among all prepared samples; its first discharge capacity is 96 mAh/g and the discharge capacity loses only 3.1% after 20 cycles. Cyclic voltammetry curves showed that LiZn_0.05Ni_0.05Mn_1.9O_3.9F_0.1 had only one reduction-oxidation peak at 4.0 V in cyclic voltammetry measurements and could offer a more stable voltage, and also had stable electrical conductivity after 20 cycles.     

Review of magnetocaloric effect in perovskite-type oxides

We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO 3-type manganese oxides, A3B2O7-type two-layered perovskite oxides, and A2B'B'O6-type ordered double-perovskite oxides). Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal (Na or K) doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+δ (0 x 0.5), and double-perovskite Ba2Fe1+xMo1-xO6 (0 ≤ x ≤ 0.3) near their respective Curie temperatures. Compared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.     

Recent progress in solid oxide and lithium ion conducting electrolytes research

Recent material developments of fast solid oxide and lithium ion conductors are reviewed. Special emphasis is placed on the correlation between the composition, structure, and electrical transport properties of perovskite-type, perovskite-related, and other inorganic crystalline materials in terms of the required functional properties for practical applications, such as fuel or hydrolysis cells and batteries. The discussed materials include Sr- and Mg-doped LaGaO₃, Ba₂In₂O₅, Bi₄V₂O₁₁, RE-doped CeO₂, (Li,La,)TiO₃, Li₃La₃La₃Nb₂O₁₂ (M=Nb, Ta), and Na super-ionic conductor-type phosphate. Critical problems with regard to the development of practically useful devices are discussed.     

Electrochemical properties of metal oxides as anode materials for lithium ion batteries

Some oxides have been investigated as alternative materials for Li-ion batteries. In particular, the In₂O₃ anodic compound, synthesized in our laboratory, and some commercial powders (PbO, PbO₂ and Fe₂O₃) were studied. The morphology of the oxides was analyzed by SEM investigation. The electrochemical characteristics obtained on composite thin-film electrodes based on these materials are here reported, in term of specific capacity and cyclability. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Angle-resolved photoemission spectroscopy of perovskite-type transition-metal oxides and their analyses using tight-binding band structure

Nowadays it has become feasible to perform angle-resolved photoemission spectroscopy (ARPES) measurements of transition-metal oxides with three-dimensional perovskite structures owing to the availability of high-quality single crystals of bulk and epitaxial thin films. In this article, we review recent experimental results and interpretation of ARPES data using empirical tight-binding band-structure calculations. Results are presented for SrVO₃ (SVO) bulk single crystals and La_{1? x} Sr _x FeO₃ (LSFO) and La_{1? x} Sr _x MnO₃ (LSMO) thin films. In the case of SVO, from comparison of the experimental results with calculated surface electronic structure, we concluded that the obtained band dispersions reflect the bulk electronic structure. The experimental band structures of LSFO and LSMO were analyzed assuming the G-type antiferromagnetic state and the ferromagnetic state, respectively. We also demonstrated that the intrinsic uncertainty of the electron momentum perpendicular to the crystal surface is important for the interpretation of the APRES results of three-dimensional materials.     

Fe-based perovskite-type oxides as excellent oxygen-permeable and reduction-tolerant materials

Development of new mixed conductors with both high oxygen permeability and phase stability under reducing atmosphere is indispensable for realizing practical MIEC systems of oxygen separation and membrane reactor. In this study, a family of Co-free Fe-based perovskite-type oxides, (Ba,Sr)(Fe,Mn)O_3−δ was prepared and their oxygen permeability and phase stability against reduction were examined. Optimum Ba doping concentration at A site was found around 30%, and Ba_0.3Sr_0.7FeO_3−δ showed highest oxygen permeability (3.0 cm³(STP)cm^− 2 min^− 1 at 900 °C) in this study. Perovskite-type oxides of the Ba–Mn–Fe–O and Ba–Sr–Mn–Fe–O systems with appropriate compositions preserved the structure even after annealing in the reducing atmosphere of 5% H₂/N₂ at 1000 °C, showing their exceeding reduction tolerance.     

High pressure-high temperature synthesis of distorted perovskite-type Cu-based oxides

Abstract

We have synthesized the rhombohedrally distorted perovskite phase of LaCuO₃ by reacting mixtures of La₂O₃ and CuO in an oxygen rich atmosphere at 1500°C and 6.5 GPa. We find this phase to be metastable; at 410°C and ambient pressure, it undergoes an irreversible transition to a tetragonal structure. By selective replacement of some or all of the La or Cu with one or more of the following elements: Ba, Ca, Cr, Ni, Pb, Sc, Sr, Ti, Y, Zn, and Zr, over 150 different alloys have been formed. Magnetic susceptibility measurements have failed to reveal the presence of superconductivity in any of these new polymorphs.     

Gate-controlled magnetic transitions in Fe_3GeTe_2 with lithium ion conducting glass substrate

Since the discovery of magnetism in two dimensions,effective manipulation of magnetism in van der Waals magnets has always been a crucial goal.Ionic gating is a promising method for such manipulation,yet devices gated with conventional ionic liquid may have some restrictions in applications due to the liquid nature of the gate dielectric.Lithium-ion conducting glass-ceramics(LICGC),a solid Li~+ electrolyte,could be used as a substrate while simultaneously acts as a promising substitute for ionic liquid.Here we demonstrate that the ferromagnetism of Fe_3 GeTe_2(FGT) could be modulated via LICGC.By applying a voltage between FGT and the back side of LICGC substrate,Li~+ doping occurs and causes the decrease of the coercive field(H_c) and ferromagnetic transition temperature(T_c) in FGT nanoflakes.A modulation efficiency for of up to ～ 24.6% under V_g=3.5 V at T=100 K is achieved.Our results provide another method to construct electrically-controlled magnetoelectronics,with potential applications in future information technology.     

A comparative study of lithium and sodium salts in PAN-based ion conducting polymer electrolytes

The conducting polymer electrolyte films consisting of polyacrylonitrile (PAN) as the host polymer, lithium triflate (LiCF₃SO₃) and sodium triflate (NaCF₃SO₃) as inorganic salts were prepared by the solution-cast technique. The pure PAN film was prepared as a reference. The ionic conductivity for the films is characterized using impedance spectroscopy. The room temperature conductivity for the PAN + 26 wt.% LiCF₃SO₃ film and the PAN + 24 wt.% NaCF₃SO₃ film is 3.04 × 10⁻⁴ S cm⁻¹ and 7.13 × 10⁻⁴ S cm⁻¹, respectively. XRD studies show that the complexation that has occurred in the PAN containing salt films and complexes formed are amorphous. The FTIR spectra results confirmed the complexation has taken place between the salt and the polymer. These results correspond with surface morphology images obtained from SEM analysis. The conductivity–temperature dependence of the highest conducting film from PAN + LiCF₃SO₃ and PAN + NaCF₃SO₃ systems follows Arrhenius equation in the temperature range of 303 to 353 K. The PAN containing 24 wt.% LiCF₃SO₃ film has a higher ionic conductivity and lower activation energy compared to the PAN containing 26 wt.%LiCF₃SO₃ film. These results can be explained based on the Lewis acidity of the alkali ions, i.e., the interaction between Li⁺ ion and the nitrogen atom of PAN is stronger than that of Na⁺ ion.     

Muonium dynamics in transparent conducting oxides

The motional and electrical properties of positively charged muonium (Mu⁺)$({\mathrm{Mu}}^{+})$ centers in single crystal β-Ga₂O₃$\mathrm{\beta }\mathrm{-}{\mathrm{Ga}}_2{\mathrm{O}}_3$ are investigated via zero field muon spin relaxation (ZF-MuSR). Below room temperature we find two distinct shallow muonium centers with ionization energies of 7 and 16 meV. Above room temperature, at least three different Mu⁺ signals are resolved; two of these are metastable while the third shows characteristics of a stable ground state. As the temperature is elevated, metastable centers undergo several transitions. We obtain the relevant barrier energies associated with these site-change transitions. By 700 K, most muons occupy the mobile ground state, and an activation energy of about 1.65 eV is inferred for Mu⁺ diffusion from the hop rates obtained for this state.