Daisuke Mori

Characterization of Electrode/Electrolyte Interface with X-Ray Reflectometry and Epitaxial-Film LiMn2O4 Electrode

Structural changes at electrode/electrolyte interface of a lithium cell were studied by X-ray reflectometry and two-dimensional model electrodes with a restricted lattice plane of LiMn 2 O 4 . The electrodes were constructed with an epitaxial film synthesized by the pulsed laser deposition method. The orientation of the film depends on the substrate plane; the (111), (110), and (100) planes of LiMn 2 O 4 grew on the (111), (110), and (100) planes of the SrTiO 3 substrates, respectively. The ex situ reflectometry indicated that a thin impurity layer covered the lattice plane of the as-grown film. The impurity layer was dissolved and a solid-electrolyte-interface-like phase appeared after the electrode was soaked into the electrolyte. A defect layer was formed in the (111) plane, whereas no density changes were detected for the other lattice planes. The in situ observation clarified that the surface reactivity depended on the lattice planes of the spinel; the defect layer at the (111) plane was stable during the electrochemical reaction, whereas a slight decrease in the film thickness was observed for the (110) plane. Our surface characterization of the intercalation electrode indicated that the surface structure changes during the pristine stage of the change-discharge processes and these changes are dependent on the lattice orientation of LiMn 2 O 4 .

Synthesis, Direct Formation under High Pressure, Structure, and Electronic Properties of LiNbO3-type Oxide PbZnO3

A novel LiNbO3-type (LN-type) lead zinc oxide, PbZnO3, was successfully synthesized under high pressure and temperature. Rietveld structure refinement using synchrotron powder X-ray diffraction (XRD) data demonstrated that LN-type PbZnO3 crystallized into a trigonal structure with a polar space group (R3c). The bond valence sum estimated from the interatomic distances indicated that the sample possesses a Pb(4+)Zn(2+)O3 valence state. Polarization could evolve as a result of the repulsion between constituent cations because PbZnO3 does not contain a stereochemical 6s(2) cation or a Jahn-Teller active d(0) cation. Distortion of ZnO6 octahedra resulting from cation shift is comparable with that of d(0) TiO6 in ZnTiO3 and MnTiO3 with LN-type oxides, which leads to stabilization of the polar structure. PbZnO3 exhibited metallic behavior and temperature-independent diamagnetic character. In situ XRD measurement revealed that the formation of LN-type PbZnO3 occurred directly without the formation of a perovskite phase, which is unusual among LN-type materials obtained by high-pressure synthesis.

High-Pressure Synthesis, Structure, Dielectric and Magnetic Properties for SrCu3Ti4O12

An A-site ordered perovskite oxide SrCu3Ti4O12 was synthesized under high pressure and temperature conditions. The sample was characterized by the synchrotron X-ray diffraction, dielectric and magnetic susceptibility measurements. The synchrotron X-ray Rietveld refinement revealed that the strontium ion fully occupied on the A-site, while the copper ion at the A′-site was slightly deficient. The dielectric constant was about 160 at 1 kHz at room temperature. The anti-ferromagnetic (AFM) order with a Néel-temperature TN of at 24.5 K was observed. The ionic radii of the A-site ion had little influence on AFM indirect exchange interaction between Cu2+ ions in ACu3Ti4O12.

Experimental and thermodynamic investigations on the stability of Mg14Si5O24 anhydrous phase B with relevance to Mg2SiO4 forsterite, wadsleyite, and ringwoodite

Abstract High-pressure high-temperature phase relation experiments in Mg14Si5O24 were performed using a 6-8 multi-anvil high-pressure apparatus in the pressure range of 12–22 GPa and temperature range of 1673–2173 K. We first found that Mg14Si5O24 anhydrous phase B (Anh-B) dissociates to Mg2SiO4 wadsleysite (Wd) and MgO periclase (Per) at about 18 GPa and 1873 K. From the results of the high-pressure experiments, the phase boundaries of 5 Mg2SiO4 forsterite (Fo) + 4 Per = Anh-B and Anh-B = 5 Wd + 4 Per were determined. In addition, the isobaric heat capacity (CP) of Anh-B was measured by differential scanning calorimetry in the temperature range of 300–770 K and the thermal relaxation method using a Physical Property Measurement System (PPMS) in the range of 2–303 K. From the measured low-temperature CP, the standard entropy (S298.15o)

Synthesis and Structures of Novel Solid-State Electrolytes

begin{array}{} (S{^{rm o}_{298.15}}) end{array}

Low temperature synthesis, structure and magnetic properties of Mn2[VO4]F

of Anh-B was determined to be 544.4(2) J/(mol⋅K). We also performed high-temperature X-ray diffraction measurements in the range 303–773 K to determine the thermal expansivity (α) of Anh-B. The obtained CP and α were theoretically extrapolated to higher temperature region using a lattice vibrational model calculation partly based on Raman spectroscopic data. Thermodynamic calculations by adopting the thermochemical and thermoelastic data for Anh-B obtained in this study and the estimated formation enthalpy for Anh-B of −13 208 kJ/mol gave phase equilibrium boundaries for 5 Fo + 4 Per = Anh-B and Anh-B = 5 Wd + 4 Per that were consistent with those determined by the present high-pressure high-temperature experiments. The results clarified that, in the Mg14Si5O24 system, Anh-B is stable between 12 and 18 GPa at the expected temperatures of the Earth’s mantle.

Characterization of electrode/electrolyte interface for lithium batteries using in situ synchrotron X-ray reflectometry—A new experimental technique for LiCoO2 model electrode

Two classes of new materials possessing ion conductivity have been developed: a lithium ion conductor and a hydride ion conductor. Conventional perovskite and ordered rock-salt structures were adopted as frameworks for lithium migration, and electrochemically stable elements such as Al, Ga, Ta, and Sc were used in the materials to facilitate their use as low-potential negative electrodes. New compositions of (Li0.25Sr0.625V(Li,Sr)0.125)(Ga0.25Ta0.75)O3, and Li0.9Sc0.9Zr0.1O2 were found to be novel oxide-based lithium ion conductors. Oxyhydrides with K2NiF4-type structures were synthesized via a high-pressure synthesis method and their use in pure hydride ion conduction was demonstrated. The La2–x–y Sr x+y LiH1–x+y O3–y oxyhydrides showed wide composition ranges of solid solution formation and the conductivity increased with anion vacancies or the introduction of interstitial hydride ions. The performance of an all-solid-state TiH2/o-La2LiHO3 (x = y = 0, o: orthorhombic)/Ti cell provided conclusive evidence of pure H– conduction.

Impedance spectroscopy of perovskite air electrodes for SOFC prepared by laser ablation method

Abstract The compound Mn2[VO4]F was synthesized using a hydrothermal synthesis route at low temperature and its crystal structure was determined from single crystal X-ray diffraction data. Mn2[VO4]F was characterized by magnetic susceptibility and specific heat capacity measurements. Mn2[VO4]F crystallizes with the triplite-type structure, space group C2/c, a = 13.451(3) Å, b = 6.6953(16) Å, c = 10.126(3) Å, β = 116.587(4)°, V = 815.6(3) Å3 and Z = 8. The structure consists of a 3D-framework built up of VO4 tetrahedra, and manganese (II) polyhedra which form chains running along the [101] and [010] directions. The coordination of the manganese cations and the connectivity between the manganese polyhedra are not defined clearly due to the disorder of the fluoride anions which form zigzag chains along [001]. The magnetic susceptibility follows a Curie–Weiss behavior above 50 K with Θ = −88 K indicating that predominant magnetic interactions are antiferromagnetic. The specific heat capacity and magnetization measurements show that Mn2[VO4]F undergoes a three-dimensional magnetic ordering at TN = 30 K and a canted weak ferromagnetism due to mixed-anion effect.