稲熊 宜之

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 Sr(2)MMoO(6)(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+(3d(5):t(2g)(3)e(g)(2)), Mo6+(4d(0))}, {Fe3+(3d(5+):t(2g)(3)e(g)(2)), Mo5+(4d(1):t(2g)(1))} and (Co2+(3d(7):t(2g)(5)e(g)(2)), Mo6+(4d(0))}. The properties of these compounds are summarized as follows: Sr2MnMoO6, semiconductive and antiferromagnetic; Sr2FeMoO6,metallic and ferrimagnetic; Sr2CoMoO6, semiconductive and antiferromagnetic.

The crystal structure and magnetic properties of new K2NiF4-type oxides, La2-2xSr2xMg1-xRuxO4(1/3 less than or equal to x less than or equal to 1), have been investigated. Powder X-ray diffraction data were best fitted by the space group I4/mmm, which indicates that the arrangement of Mg2+ and Ru4+ is disordered. An increase in x from 1/3 first decreased the effective magnetic moment of ruthenium from 3.6 to 3.4 mu(B) then increased it up to 5.0 mu(B). The tetragonal distortion of(Mg,Ru)O-6 octahedra continuously decreased from 1.11 for x = 1/3 to 1.05 for x = 1.

Substitution of Na, K, Rb, and Sr for La in the perovskite type structure complex oxide LaMnO3 were carried out and their structure and properties were investigated, Lattice symmetry of the samples sintered at 1393 K in O-2 gas flow was found to be rhombohedral. Rietveld refinement to X-ray diffraction data revealed a systematic decrease of the lattice distortion with substitution, The change of temperature dependence of resistivity from semiconducting to metallic and the increase of the ferromagnetic transition temperature with substitution were recognized and found to be closely related to structural changes, The anomalies in the Seebeck coefficient at the ferromagnetic transition temperature suggest a strong correlation between the electronic state and magnetism. (C) 1996 Academic Press, Inc.

Influences of Site Percolation and local Distortion on Lithium Ion Conductivity in Perovskite-type Oxides La<sub>0.55</sub>Li<sub>0.35-<i>x</i></sub>K<i><sub>x</sub></i>TiO<sub>3</sub> and La<sub>0.55</sub>Li<sub>0.35</sub>TiO<sub>3</sub>-KMO<sub>3</sub> (M =Nb and Ta)

The influence of carrier (lithium and vacancy) concentration on the lithium ion conductivity in perovskite-type oxides La(2/3-x)Li(3x)square(1/3-2x)TiO(3) and yLa(0.5)Na(0.5)TiO(3)-(1-y)La(0.55)Li(0.35)square(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 was electrochemically inserted into perovskite-type oxide LaxMnyO3 with both rhombohedral and orthorhombic symmetries. Ferromagnetic transition temperature(T-c) of lithiated rhombohedral LizLaxMnyO3 first decreased then increased with an increase in z. This result was clearly explained by the change in the structure with the insertion.

Structural analysis and measurement of magnetic susceptibility were carried out for the 6H-type hexagonal compounds Ba(3)Cr(2)MO(9) (M = Mo and W). The space groups of Ba3Cr2MoO9 and Ba3Cr2WO9 were determined by Rietveld analysis of powder X-ray diffraction data to be P6(3)/mmc and <P(6)over bar 2c>, respectively. Chromium ions were found to occupy the centers of face-shared octahedra, with tungsten or molybdenum ions at the centers of corner-shared octahedra. The magnetic susceptibilities of Ba3Cr2MoO9 and Ba3Cr2WO9 were explained using the two-sublattice and dimer models, respectively; the difference may be due to the difference in the valence states of Cr and Mo in Ba3Cr2MoO9 and Cr and W in Ba3Cr2WO9. (C) 1995 Academic Press, Inc.

Structure analysis and measurement of resistivity under both isostatic pressure smaller than 1.1 GPa and magnetic field of 1 T were carried out for rhombohedral La(1-x)A(x)MnO(3) (A = Na, K, Rb, and Sr). A close relationship was confirmed to hold between T-c and the bond distance of Mn-O. The application of the isostatic pressure up to 1.1 GPa decreased the resistivity more than 60% below T-c but this effect was smaller above T-c. This pressure dependency was explained by the decrease in bond distance of Mn-O under pressure. Magnetic resistance for La0.87K0.06Mn0.97O3 was found to be - 10%/T, which is the same order of the previous reports for La(1-x)A(x)MnO(3) (A = Ca, Sr, Ba).

The effects of Ca and Ba substitutions for Sr on the structure and properties of Sr2IrO4 were studied. increase in the Ir-O(2)-Ir bond angle in the IrO2 plane was found after the substitutions of Ca and Ba for Sr. However, the Ir-O(2) distance is found to be unchanged by the Ba substitution, while it decreases by the Ca substitution. Regardless of these structural changes, the magnetic transition temperature at 240 K was found to be unchanged. Semiconductive behavior of the resistivity was found for all compounds with the increase in activation energy above 200 K. Both the electrical resistivity and the Seebeck coefficient showed no remarkable anomaly around the magnetic transition temperature.

The structure of the two-dimensional conductor Sr2RhO4 was refined by powder X-ray diffraction analysis at room temperature. Sr2RhO4 crystallizes with the symmetry of space group I4(1)/acd (No. 142-2), isostructural with Sr2IrO4, and the room temperature lattice parameter a = 0.54516(1) nm and c = 2.57539(4) nm. The rotating angle of RhO6 octahedra about the c axis is 10 degrees. The structural data was found to be almost same as that for semiconducting and antiferromagnetic Sr2IrO4. (C) 1995 Academic Press, Inc.

The lithium ion conductivity in the perovskite-type xLiTaO(3)-(1-x)SrTiO3 solid solution (0.30 less than or equal to x less than or equal to 0.50) has been investigated. The highest ionic conductivity of 5.5X10(-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.

Lithium was electrochemically inserted into perovskite oxides, SrVO3-delta, La2/3TiO3-delta and (La, Li)TiO3-delta, by using a galvanic cell: Li\1M LiClO4 in PC\perovskite oxide. The tetravalent transition metal ion (Ti, V) can be reduced to the minimum valence of 3 by lithium insertion. This fact was explained by the effect of valence on the lattice self-potential and site-potential in the ideal perovskite oxide ABO(3). We tried to explain the lithium insertion and high lithium conductivity in the perovskite oxide from the view point of electrostatic potentials.

A new method for the electrochemical synthesis of oxide thick film in molten salt was developed. The following galvanic cell was assembled, and the electrolysis was carried out at 973 K Pt, metal\(50-x/2) mole percent (m/o) KCl-(50-x/2) m/o NaCl-x m/o additive\(O2-)YSZ\O-2, Pt where the additive was an oxide or a chloride containing the metal ions of the anode. When the additive was dissolved and ionized in the molten salt, its oxide film formed on the stabilized zirconia surface. At this time, metal ions derived from the additive were carried to the stabilized zirconia surface under an electric field, and reacted with oxide ions, coming from the oxygen electrode through zirconia solid electrolyte, to form the oxide film.

Lithium ions were electrochemically inserted into perovskite-type oxides SrVO3-delta and La0.50Li0.37TiO2.94 using galvanic cell: Li\1 M LiClO4 in PC\SrVO3-delta or La0.50Li0.37TiO2.94. It is found that the lattice parameters of SrVO3-delta will be increased and the discharge capacity of SrVO3-delta will be decreased as delta 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-delta and La0.50Li0.37TiO2.94 were determined to be the values in the range from 10(-8) to 10(-12) cm(2) 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.

Polycrystalline materials of BaSn1-xSbxO3-delta and Ba1-yLaySnO3-delta 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-delta and y < 0.052 for Ba1-yLaySnO3-delta. The X-ray photoemission spectroscopy measurements showed the valence of antimony and tin is mixed in our samples of BaSn1-xSbxO3-delta. At lower temperature, magnetic susceptibilities of BaSn1-xSbxO3-delta and Ba1-yLaySnO3-delta 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.

The pressure dependence of the phase-transition temperatures for oxygenated La2CuO4.035 single crystals was investigated in the pressure range &lt 14 kbar. Three successive phase transitions, one at 295 K with second-order character, one around 265 K with martensitic-transition character, and the other around 222 K with first-order character, were found to be suppressed under pressure. The pressure coefficient of the superconducting temperature dTc/dp turned from -0.5 to +0.7 K/kbar when the three successive phase transitions were suppressed by pressure. © 1995 The American Physical Society.

The ionic conductivity of the polycrystalline La-0.52+/-0.01 Li-0.35+/-0.01 TiO2.96+/-0.02 has been measured as a function of hydrostatic pressure up to 1.2 GPa in the temperature range between 238 and 294 K. The conductivity decreased with an increase in pressure. The value of activation volume for ionic motion derived from the data is positive and almost invariable, between 1.6 +/- 0.2 and 1.7 +/- 0.2 cm(3)/mol, in the temperature range measured. This implies that a dilatation of the lattice occurs during the transport process. The activation energy of the ionic conductivity slightly increased with an increase in pressure. The mechanism of the ionic conduction is discussed on the basis of these results.

The microwave dielectric characteristics of ilmenite titanates, M(2+)TiO(3) (where M(2+)=Ni, Mg and Mn) and (Mg(0.95)M(0.05)(2+)TiO(3) (where, M(2)=Ni, Mg, Co and Mn) series, have been investigated as a function of ionic radius of M(2+) and (Mg(0.95)M(0.05)(2+))(2+) ions, respectively. The ilmenite titanates have high Q value and low dielectric constant due to the isolation of TiO6 octahedra by the MO(6) octahedron layer and cation vacancy layer in comparison with the perovskite titanates. The existence of localized 3d electrons in N2+(3d(8)) and Mn2+(3d(5)) is concerned with the microwave dielectric properties of the M(2+)TiO(3) series. The dielectric constant, epsilon(r) at 10 GHz of the (Mg(0.9)5M(0.05)(2+)) TiO3 series shows the minimum value around the average ionic radius of 0.721 Angstrom A while the Q value shows a maximum, probably due to a local lattice distortion. The Mg(0.9)5Co(0.05))TiO3 compound shows a maximum Q value of 23,000 at 10 GHz, dielectric constant of 16.8, and tau(f) of -54 ppm/K.

Heat capacities and electrical moduli of high lithium ion conductor Li0.35La0.51TiO2.94 Were measured below 300 K. A glass transition was observed at T(g) = (102 +/- 2) K as due to the freezing-in of positional disorder of lithium ions. The associated heat capacity jump was found to be (0.03(+0.03/-0.01))JK-1 mol-1 at 125 K. The energy of the excited state as referred to the ground state was evaluated from the jump to be ca. 9 kJ mol-1. The calorimetric and electrical relaxation times for the rearrangement of lithium ions were well fitted by a straight line on an Arrhenius plot, and the activation energy of the process was derived to be (32.0 +/- 0.1) kJ mol-1. A potential close relation was suggested to exist in general between the high ionic conductivity and the positional disorder of mobile ions.

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 (sigma = 1.5 X 10(-3)S cm-1 at 300 K) than the pure lanthanum lithium titanate.

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 orthorhombic (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.

The superconducting transition temperature T(c) and the Hall coefficient have been measured on IBi2.2Sr1.8CaCu2O8+y single crystals under hydrostatic pressure. The T(c) linearly decreases at the rate dT(c)/dP approximately -3.5 K/GPa, indicating the facts that the charge transfer occurs between intercalated iodine atoms and CuO2 layers, and the hole concentration situates in the overdoped region. The facts have been further identified by our Hall-coefficient measurements at ambient pressure, showing an increase of the hole concentration after intercalation. The number of holes transferred from intercalated iodine atoms was calculated to be 0.3 per iodine atom. The pressure derivative of the Hall coefficient is -0.39 X 10(-3) cm3 C-1 GPa-1, which is approximately twice as large as the value on the pristine crystal, indicating the valence change of the intercalated iodine under pressure.

The resistance and A.C. susceptibility measurements for SrRuO3 under a hydrostatic pressure were carried out. T(C) decreases linearly with an increase in applied pressure at a rate partial derivative T(C)/partial derivative P = -7.9 K.GPa-1 . T(C) decreases linearly with an increase in Ca content at a rate partial derivative T(C)/partial derivative x = -2.6x10(2) K. These phenomena were discussed on the nallow band model.

K2NiF4-type solid solution system Sr2-xLaxRhO4 was prepared and the structure and electrical and magnetic properties were investigated. The result of powder x-ray-diffraction analysis shows stretching of the a and b axes and shortening of the c axis with an increase of x. The positive temperature dependence of the resistivity in the range x less-than-or-equal-to 0.15 disappears with an increase of x greater than 0.15. The temperature dependence of the activation energy of carriers suggests two-dimensional variable range hopping-type conduction in the semiconducting range. The localized magnetic moment of the Rh ion is greater than the calculated value based on the low spin state, and the antiferromagnetic interaction among Rh ions decreases with an increase of x. A magnetic anomaly around 60 K observed for Sr2RhO4 diminishes with an increase of x and vanishes at x = 0.20. A positive Seebeck coefficient suggests hole conduction in this system and the Fermi energy obtained from the linear temperature dependence of the Seebeck coefficient on T decreases with x, which can be explained from the decrease of holes with the substitution of low spin Rh3+(4d6) for Rh4+(4d5).

New perovskite compounds Sr(Li1/4Ru3/4)O3, Sr(Na1/4Ru3/4)O3, (Sr1/2La1/2)(Mg1/4Ru3/4)O3 and (Sr7/8La1/8)(Mg1/4Ru3/4)O3 have been prepared. The crystal structures of these compounds were determined by powder X-ray Rietveld analysis. The crystal structure of these compounds was orthorhombic with space group Pnma. Electrical resistivity and magnetic susceptibility were measured for the samples with the nominal ruthenium valences from 4.0+ to 5.0+. In this study, the crystal structure, electrical conductivity and magnetic properties of the new ruthenium perovskite compounds are discussed.

The resistance and Hall coefficient of a Bi2.2Sr1.8CaCu2O8+y single crystal have been measured under pressure. It is shown from our result that the pressure coefficient of dT(c)/dP changes from positive to negative with increasing pressure and the maximum superconducting transition temperature appears at a pressure of about 1.05 GPa. The Hall-coefficient result shows a monotonic increase of hole concentration with pressure up to 1.19 GPa. The maximum of the superconducting transition temperature induced by pressure in Bi2.2Sr1.8CaCu2O8+y can be interpreted in terms of the hole concentration passing through an optimal value under pressure.

It has been discovered that the polycrystalline lithium lanthanum titanat Li0.34(1)-1La0.51(1)TiO2.94(2) shows high ionic conductivity more than 2 x 10(-5) S cm (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) angstrom. 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 X 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 Li insertion into a vacant site and then an electron carrier was introduced.

Single crystals of La2-xBaxCuO4 with 5 mm diameter and 25 mm length have been grown by the traveling solvent floating zone (TSFZ) method. The composition of the single crystal containing maximum Ba content and showing a superconducting transition at 30 K was determined to be La1.935Ba0.065CuO4. Electrical resistivities along the c-axis and in the ab-plane reveal significant anisotropy. Magnetic susceptibilities have been measured under a field of 50 Oe from 5 to 50 K. Under fields H perpendicular-to ab-plane and H parallel-to ab-plane, the single crystal demonstrates 3.6% and 0.7% Meissner fractions, respectively, at 5 K.

The oxygen nonstoichiometry in the high T_c superconductor Ba_2SmCu_3O_<7-x> was determined over the temperature range of 350° to 900℃ under the oxygen partial pressure between 10^<-3> and 1 atm, with the thermogravimetric measurement calibrated by the iodometric titration technique. The temperature dependency of the nonstoichiometry indicates that a phase transition occurs at a temperature between 600°and 700℃.