Tetsurō Nakamura

High ionic conductivity in lithium lanthanum titanate

It has been discovered that the polycrystalline lithium lanthanum titanate Li0.34(1)La0.51(1)TiO2.94(2) shows high ionic conductivity more than 2 × 10−5 S cm−1 (D.C. method) at room temperature, which is compared with that of Li3.5V0.5Ge0.5O4. This compound has cubic perovskite structure whose cell parameter is 3.8710(2) A. By a.c. impedance analysis, the equivalent circuit of the sample could be divided into two parts; bulk crystal and grain boundary. The ionic conductivity of the bulk part is as high as 1 × 10−3 S cm−1 at room temperature. Such a high conductivity is considered to be attributed to the presence of a lot of equivalent sites for lithium ion to occupy and freely move in this perovskite. In addition, this compound is easy to react with lithium metal and the electronic conductivity has become much higher than before being in contact with Li. It can be explained that titanium ion was reduced by ii insertion into a vacant site and then an electron carrier was introduced.

Candidate compounds with perovskite structure for high lithium ionic conductivity

Abstract Compounds with perovskite structure which were candidates for high ionic conductivity were searched and synthesized on the basis of the knowledge of lanthanum lithium titanates and their ionic conductivity was investigated. The free volume for lithium ions to migrate, and the lithium and vacancy concentrations on the A-site play important roles for the ionic conductivity in the perovskite structure. Lanthanum lithium titanate substituted with 5 mol% Sr had a larger free volume and showed higher ionic conductivity of the bulk part ( σ =1.5×10 −3 S cm −1 at 300 K) than the pure lanthanum lithium titanate.

High lithium ion conductivity in the perovskite-type compounds Ln12Li12TiO3(Ln=La,Pr,Nd,Sm)

Perovskite-type compounds La0.51(1)Li0.34(1)TiO2.94(2), Pr0.56(2)Li0.34(2)TiO3.01(3), Nd0.55(2)Li0.34(1)TiO3.00(3), and Sm0.52(1)- Li0.38(1)TiO2.97(2) were synthesized and their structures and lithium ion conductivities were investigated. Symmetry of the lattice changes from cubic for La0.51(1)Li0.34(1)TiO2.94(2) to orthombic (space group: Pmmm) for Pr0.56(2)Li0.34(2)TiO3.01(3) and Nd0.55(2)Li0.34(1)TiO3.00(3), and to orthorhombic (Pmma or Pnma)for Sm0.52(1)Li0.38(1)TiO2.97(2). Lithium ion conductivities decrease with decreasing the radii of lanthanide ions, which play the role of spacer for lithium ions.

Nonstoichiometric behavior and phase stability of rare earth manganites at 1200°C: (1). LaMnO3

The perovskite phase LaMnO3±λ was revealed to have nonstoichiometry ranging from 2.947 to 3.079 under the oxygen partial pressure below logPO2(atm)=0 at 1200°C. The presence of the reductive perovskite phase LaMnO3−λ with a more distorted structure than the monoclinic one was ascertained. The free energy change of oxidative reaction in MnO+1/2La2O3+1/4O2=LaMnO3 was determined to be ΔG°=19500±200cal at 1200°C. D.C. electrical conductivities of LaMnO3±λ perovskites at room temperature became higher with increasing oxygen content. Magnetic measurements were also made.

Pressure dependence of the magnetic transition temperature for ferromagnetic SrRuO3

Abstract The resistance and A.C. susceptibility measurements for SrRuO3 under a hydrostatic pressure were carried out. TC decreases linearly with an increase in applied pressure at a rate ∂T C ∂P = −7.9 K·GPa −1 . TC decreases linearly with an increase in Ca content at a rate ∂T C ∂x = −2.6×10 2 K . These phenomena were discussed on the nallow band model.

Thermogravimetric study of rare earth manganites AMnO3 (A=Sm,Dy,Y,Er,Yb) at 1200°C

Abstract The free energy changes of formation of SmMnO 3 , DyMnO 3 , YMnO 3 , ErMnO 3 and YbMnO 3 were determined to be −14.3, −11.1, −11.4, −11.2 and −10.5kcal/mol, respectively, at 1200°C on the basis of the equilibria. Simultaneously, the nonstoichiometry was also investigated in the oxygen partial pressure below logP O2 [atm]=0. The free energy change and the width of nonstoichiometry in these ternary oxides were revealed to be dependent on the radius of rare earth ion. YbMnO 3 showed no deviation from stoichiometry in contrast with LaMnO 3 .

Superconductivity, magnetism and oxygen nonstoichiometry of Ba2Y(Cu1−xMx)3Oy (M = Zn and Ni)

Abstract The effects of both the atomic substitutions and the change of oxygen content on the superconductivity and magnetic properties of Ba 2 Y ( Cu 1− x M x ) 3 O y (M = Zn and Ni) solid solution systems have been investigated. The Ni ion in the solid solution was found to be trivalent and have a magnetic moment of ≈ 2.4μ B . At the same oxygen content, the substitution of Cu by Zn always gives a steeper depression of T c than the substitution by Ni. The dependence of T c on the oxygen content indicates that T c is not depressed by the change of the hole concentration through the substitutions of Cu by Zn and Ni. The Zn ion in the solid solution plays a similar role to the over-doped holes in the two aspects of (i) weakening significantly the antiferromagnetic correlation among Cu spins and (ii) inducing a deviation of the band structure from the simple Mott-Hubbard model.

Valence stability of molybdenum in alkaline earth molybdates

Abstract Presence of oxygen stability range in ternary oxides was experimentally verified for molybdenum(IV) perovskites, and the widths of stability range were determined of BaMoO 3 , SrMoO 3 and CaMoO 3 . Moreover, the tetravalent state of molybdenum was found to be more strongly stabilized in these compounds than in its binary oxide. A concept of lattice self-potential was examined in order to explain this phenomenon. Contribution of A-cation to the retention of high valence state of B-cation in the perovskite ABO 3 was also discussed.

The effect of La substitution on the superconductivity of Ba2YCu3Oy

Abstract The (Ba 1− x La x ) 2 YCu 3 O y solid solution has been characterized for its superconducting transition temperature T c , lattice parameters, oxygen content and carrier concentration. T c is found to have a relation to the oxygen introduction by La doping. The depression of T c in the region of x > x c ( x c =0.05) is attributed to the formation of [Cu(I)O 5 ] pyramids or [Cu(I)O 6 ] octahedra. A model is proposed to interpret the influence of [Cu(I)O 5 ] pyramids on the superconductivity. The fraction of uncooperative atoms in Cu(II)O 2 sheets is found to be a common parameter of T c for several kinds of cation substituted Ba 2 YCu 3 O y systems.

Electrical properties of BaSnO3 in substitution of antimony for tin and lanthanum for barium

Polycrystalline materials of BaSn1−xSbxO3−δ and Ba1−yLaySnO3−δ were prepared. Substitutional solubilities of antimony for tin and lanthanum for barium, respectively, in BaSnO3 were obtained to be x=0.18 for BaSn1−xSbxO3−δ and y<0.052 for Ba1-yLaySnO3−δ. The X-ray photoemission spectroscopy measurements showed the valence of antimony and tin is mixed in our samples of BaSn1−xSbxO3−δ. At lower temperature, magnetic susceptibilities of BaSn1−xSbxO3−δ and Ba1−yLaySnO3−δ satisfy the Curie law, indicating the existence of non-interacting localized electrons at the Sn4+ site, and forming a Sn4++e− state in these systems. By substitution of antimony and lanthanum in BaSnO3, the conductive properties are semiconductor-like. To explain this conductive behaviour, three types of mechanism were taken into consideration.