Yoshiyuki Inaguma

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.

Dielectric properties of a-site deficient perovskite-type lanthanum-calcium-titanium oxide solid solution system [(1 − x)La23TiO3 − xCaTiO3 (0.1 ≤ x ≤ 0.96)]

Solid solution system of the double perovskite La23TiO3 and the GdFeO3-type perovskite CaTiO3, (1 − x)CaTiO3 — xLa23TiO3, has been prepared to investigate the crystal structure and the dielectric properties. In this system, the structure changed from pseudo-cubic perovskite to tetragonal double perovskite at x ≈ 0.7, and to orthorhombic double perovskite at x ≈ 0.9. Microwave dielectric measurement showed a decrease in dielectric constant and temperature coefficient of the resonant frequency and an increase in Q value with increasing x. The sample with x = 0.96 showed excellent microwave characteristics, especially high Q(2700) along with high er(90) at 10 GHz. In the low frequency dielectric measurement, dielectric relaxation could be observed in the composition range x ≤ 0.3. The dielectric relaxation showed strikingly different behaviors depending on the annealing process in oxygen after sintering.

Valency pair and properties of 1:1 ordered perovskite-type compounds Sr2MMoO6 (M = Mn,Fe,Co)

Abstract In order to investigate the role of superexchange interaction among 3d and 4d orbitals of transition metal ions via oxygen ions. 1:1 ordered perovskite-type compounds Sr2MMoO6 (M = Mn.Fe.Co) were prepared and their structures and properties were examined. Structural analysis using the powder X-ray diffraction data revealed that all of these compounds have a 1:1 ordered arrangement in their B-sites. Measurements of electrical resistivity and magnetic susceptibility revealed that these compounds have the valency pairs of Mn2+ (3d5:t2g3eg2), Mo6+ (4d0). Fe3+ (3d5:t2g3eg2), Mo5+ (4d1:t2g1) and Co2+ (3d7:t2g5eg2), Mo6+ (4d0). The properties of these compounds are summarized as follows: Sr2MnMoO6, semiconductive and antiferromagnetic: Sr2FeMoO6, metallic and ferrimagnetic: Sr2CoMoO6, semiconductive and antiferromagnetic.

Influences of carrier concentration and site percolation on lithium ion conductivity in perovskite-type oxides

Abstract The influence of carrier (lithium and vacancy) concentration on the lithium ion conductivity in perovskite-type oxides La 2 3 − x Li 3x □ 1 3 − 2x TiO 3 and yLa 0.5 Na 0.5 TiO 3 −(1 − y ) La 0.55 Li 0.35 □ 0.1 TiO 3 solid solutions has been investigated from the view of percolation theory. Consequently, the ratio of lithium to vacancy concentration and site percolation were found to be predominant factors in lithium ion conductivity of perovskite-type oxides.

Lithium ion conductivity in the perovskite-type LiTaO3-SrTiO3 solid solution

The lithium ion conductivity in the perovskite-type xLiTa0 3 -(1 - x)SrTiO 3 solid solution (0.30 ≤ x ≤ 0.50) has been investigated. The highest ionic conductivity of 5.5 X 10 -4 S cm -1 at 300 K appears at x = 0.50. The ion conductivity decreases with a decrease in x and then rapidly decreases in the vicinity of x = 0.30. This threshold for the ion conductivity is the same as the site percolation threshold for a simple cubic lattice. This indicates that the lithium ion conduction occurs three-dimensionally among the A-sites of the perovskite.

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.

Oxide cathode with perovskite structure for rechargeable lithium batteries

Lithium ions were electrochemically inserted into perovskite-type oxides SrVO3−δ and La0.50Li0.37TiO2.94 using galvanic cell: Li|1 M LiClO4 in PC|SrVO3−δ or La0.50Li0.37TiO2.94. It is found that the lattice parameters of SrVO3−δ will be increased and the discharge capacity of SrVO3−δ will be decreased as δ increased. At the composition where all of A-site vacancies in La0.50Li0.37TiO2.94 are just occupied by the lithium ions, the lattice parameter shows a sudden increase. The chemical diffusion coefficients of lithium ions in SrVO3−δ and La0.50Li0.37TiO2.94 were determined to be the values in the range from 10−8 to 10−12 cm2 s−1. Both oxides can be considered as a useful cathode of rechargeable lithium batteries. The charge/discharge characteristic can be improved by mixing of a small amount of carbon powder with the oxide.

High temperature quantum paraelectricity in perovskite-type titanates Ln1/2Na1/2TiO3 (Ln = La, Pr, Nd, Sm, Eu, Gd and Tb)

Abstract The La3+ ion of a quantum paraelectric perovskite La1/2Na1/2TiO3 was substituted with the smaller tripositive lanthanide ions Ln3+. The X-ray structural study and Rietveld refinement of Ln1/2Na1/2TiO3 for Ln=Pr to Tb showed that they are synthesized as orthorhombic perovskite structure with the space group Pnma. Their lattice parameters and dielectric constants decreased from Pr to Tb with an increasing volume of TiO6-octahedron. A high temperature quantum paraelectricity was found for Ln = Pr to Eu. Because of negative extrapolated Curie temperature, the process of explanation used for the typical quantum paraelectric SrTiO3 is not applicable to the quantum paraelectricity in Ln1/2Na1/2TiO3 for Ln = La ∼ Eu.