稲熊 宜之

Lithium ion-conducting perovskite-type oxides, e.g., La 2/3-xLi3xTiO3 show high ionic conductivities as high as 10-5-10-3 Scm-1 at room temperature. Their high conductivities are attributed to the percolation-controlled diffusion of lithium ions via vacancies in the A-site-deficient perovskites (general formula of perovskite-type oxide: ABO3). The strong correlation between structure and percolation-controlled diffusion in the perovskites is primarily referred to the arrangement of A-site ions, and the "bottleneck" square-surrounded by four oxygen ions. The bottleneck size, i.e., the repulsion for lithium ions by the electronic clouds of oxygen ions, is dependent on the distortion and tilt of the BO6 octahedra, which relate to the difference of skeletal ions, A and B cations, i.e., tolerance factor and their chemical characters, and is the predominant factor of the activation energy for ion migration. These findings were confirmed by powder X-ray and neutron structural refinements, composition, temperature and hydrostatic pressure dependences of ionic conductivities, and molecular dynamics simulation.

N-2 adsorption on Cu-organic crystals [Cu(bpy)(2)( BF4)(2)] (bpy=bipyridine) at 77K begins suddenly at P/P-0=0.1. This unique adsorption is named gate adsorption. Gate adsorption is associated with the change of crystal structure from GCMC and dynamic GCMC simulations. An expansion of 10% opens internal pore spaces in the crystal, giving rise to gate adsorption. The complete filling of the internal spaces with N-2 molecules induces an expansion of 30%.

A rhomboidal distorted perovskite HgTiO3 with the unit cell parameters a = 5.3781 angstrom and c = 13.604 angstrom (Z = 6) was synthesized under 6 GPa at 600 degrees C for 30 minutes, using a mixture starting material HgO and TiO2 in a closed Au-capsule. Through investigations on the relationship between its crystal structure and applied pressure by the synchrotron X-ray beam (wavelength = 0.72000 angstrom ) at room temperature, we found a rhombohedral distortion decreased when the pressure increased and the symmetry approached to the cubic under a pressure of 2.3 GPa. Above room temperature, some abnormalities were observed from the measurements of differential scanning calorimetry (DSC) and dielectric property. These results suggested that HgTiO3 is a ferroelectrics at room temperature.

The synthesis of PbFeO2F is achieved using a solid-state reaction under high pressure. This perovskite crystallizes in SG Pm (3) over barm (No. 221) with a = 0.39991 (1) nm. The Rietveld refinement using powder X-ray diffraction data shows that the mean structure of this compound can be characterized as follows: (1) the Pb ion statically shifts from the 1a Wyckoff position in the twelve (110) direction toward anions (O, F), and (2) the Fe ion is located in a single crystallographic site. In contrast, hyperfine data estimated from Mossbauer spectra at different temperatures suggest the existence of different Fe sites, and the isomer shift is consistent with the presence of high-spin (HS) Fe3+ ions located in FeO4F2 octahedral units, where anions are randomly distributed. Such a distribution thus favors two prevailing Fe sites, namely cis and trans. No evidence of O/F ordering in PbFeO2F was detected by electron diffraction experiments. Finally, in-field Mossbauer spectra unambiguously reveal that PbFe2OF behaves as an antiferromagnet, which is consistent with static magnetic measurements.

We report the results of a neutron powder diffraction study of the La0.62Li0.16TiO3 perovskite that determined the diffusion path of lithium cations at room temperature. At 77 K, the Li cations are located at the 2c site (Wycoff notation of the Cmmm space group) on the (002) La deficient layer, while, at room temperature, they are spread over a wide area and migrate following the 2c-4f-2c or 2c-2d-2c tie line on the (002) layer. The probability density of Li cations has a minimum between the 2c and 4f or between the 2c and 2d positions on the diffusion path in contrast to the previous reports where the bottleneck has been thought to be located at the 2c, 2d, and 4f positions. On the basis of the present structural model, the Li-cation conductivity is discussed in terms of a two-dimensional bond-percolation model for Li-cation diffusion. It was found that the vacancy at the La site is essential for the Li-cation conduction.

A hexagonal perovskite HgTiO3 with the unit cell parameters a = 5.3781 angstrom and c = 13.604 angstrom (Z = 6) was synthesized under 6 GPa at 600 degrees C for 30 minutes, using a mixture starting material HgO and TiO2 in a closed Au-capsule. Through an investigation on the relationship between its crystal structure and applied pressure by the synchrotron X-ray beam (wavelength = 0.72000 angstrom) at room temperature, we found a rhombohedral distortion decreased with increasing pressure and the symmetry approaches to the cubic under a pressure of 2.3 GPa. Above room temperature, we observed some abnormalities from measurement results both in DSC and dielectric constant. These results suggested that HgTiO3 is a ferroelectrics at room temperature.

Novel oxynitrides, LiTinOxNy (n = 1, 2, 3, 4 and 8) were synthesized by sintering under NH3 gas atmosphere. These compounds have rocksalt-type structure and the existence of cation vacancies is suggested. While the lattice parameters of these compound slightly vary, obvious tendency for the Li or nitride content is not found. For these compounds, the temperature dependence of the electronic conductivity shows the semiconducting behavior. However, the measurement of magnetic susceptibility and the Seebeck coefficient suggest that the transport in these compound is metallic. The electric conductivity seems to be dominated by the resistance of the grain boundary and the transport property of these compounds is metallic. (C) 2004 Elsevier Ltd. All rights reserved.

Cubic pyrochlore Pb2Ru2O6.50+/-0.02 single crystals were grown from a PbO flux by a slow-cooling method under ambient atmosphere. The obtained crystals were black and formed quasi-cubes and cuboctahedra. The largest crystal with a size up to 9 x 7 x 4 mm(3) was grown from the mixture of RuO2 and PbO with a molar ratio RuO2/PbO = 1/9, which was heated to 1250 degreesC, held for 10 h, and then cooled at a constant rate of 5.0 degreesC/h to 950 degreesC. It was found that the vaporization of PbO is important for crystal growth. The electronic resistivities for the crystal were 2.3 x 10(-4) Omegacm at 300 K and 2.0 x 10(-6) Omegacm at 2K, respectively. The temperature dependence of the resistivity indicates that this compound is metallic and the DC magnetic susceptibility reflects the delocalized character for electrons of Ru. (C) 2004 Elsevier B.V. All rights reserved.

The synthesis of the perovskite Li0.3La0.566TiO3 by a Pechini-type polymerizable precursor method is described. TGA-DTA analysis was carried out on the precursors, and powder XRD analysis was performed on the final products obtained by heating the precursors over a temperature range from 600 to 900 degreesC during 2 h. Highly pure and crystalline powders were obtained by this method. The morphology of the powder after heating at 900 degreesC was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The determination of the grain size by an optical method shows the formation of small grains around 100 nm in size that aggregate. This chemical method allowed us to obtain well crystallized lithium lanthanum titanate (LLTO) at a much lower temperature and with a shorter synthesis time in comparison to the conventional solid-state reaction method.

We synthesized furnace-cooled (La2/3 - 1/3pLip)(Mg1/2W1/2)O-3 (LLMW) and quenched (La2/3 - 1/3pLip)(Mg1/2W1/2)O-3 (LLMWq) and investigated Li ion conductivity for these compounds. Activation energy was found to decrease with Li content for LLMW and LLMWq, while the obvious lattice contraction accompanied with Li content was not observed. For LLMW, ordered arrangement of the A-site ions was varied with Li content which seems to be responsible for the decrease in the activation energy. As results of structure refinements of LLMWq, it was revealed that covalent character of W-O bond increased with Li content. It is considered that the Coulomb repulsion between W and Li ions dominates the activation energy and that the increase in the covalent character of the W-O bond with Li content is the reason for the decrease in the activation energy. (C) 2004 Elsevier B.V. All rights reserved.

Stabilization of a perovskite-type solid solution (1-x) PbTiO3-x BiScO3 with xgreater than or equal to0.45 was demonstrated by high-pressure synthesis, and the phase diagram and the ferroelectric properties of the solid solution were investigated. The crystal symmetry of the perovskite subcell change in turn from tetragonal, to rhombohedral, to pseudocubic, to monoclinic, and then to triclinic as x increases. It was found that the tetragonal, rhombohedral, and pseudocubic phases are ferroelectric, while the monoclinic phase is not. In the morphotropic phase boundary in the vicinity of x=0.37 between tetragonal and rhombohedral phases, the maximum electromechanical coupling factor and the minimum coercive electric field were just like those observed in other Pb-based ferroelectric perovskites. In addition, relaxor behavior in the dielectric constant was observed in the vicinity of x=0.5. (C) 2004 American Institute of Physics.

The crystal structure of the fast ionic conductor Li0.18La0.61TiO3 perovskite-type was determined at 5 K by neutron diffraction (ND) experiments in samples cooled slowly and quenched from 1600 K. In both cases, the perovskite displayed superstructures of the elementary perovskite. In the slowly cooled sample, a 2a(p),2ap,2ap superstructure with orthorhombic symmetry was detected (Cmmm space group). The main characteristics of this structure are the out-of-phase tilting of TiO6 octahedra in the [010] direction, and the ordering of La vacancies in alternate planes along the c-axis. In samples quenched in liquid nitrogen from high temperature, La and vacancies become disordered and the structure adopts a rhombohedral root2a(p),root2a(p),2root3a(p) symmetry (R (3) over barc space group). In this structure the octahedral tilting is produced along the three crystallographic axes as a consequence of the disordered arrangement of the La and the vacancies. A detailed analysis of Fourier difference maps in both samples revealed the preference of Li for the 4-fold coordination at the center of square windows that connect contiguous A-sites of the perovskite.

A perovskite Bi(Ni1/2Ti1/2)O-3 was successfully synthesized under high pressure 6 GPa. This compound has orthorhombric cell with the parameters, a = 2a(m)sin(beta/2) = 0.5626(2) nm, b = 4b(m) = 1.5681(6) nm, and c = 2c(m)cos(beta/2) 0.5548(2) nm containing eight monoclinic primitive perovskite unit with the parameters, a(m) = c(m) = 0.39507(7) nm, b(m) = 0.39203(15), and beta = 90.80(2)degrees, and the lattice distortion is expected to be antiferroelectric. In addition, the sudden increase in the dielectric constant accompanied by the anomaly of dielectric loss was observed at 490 K as the temperature increases. This is though to correspond to the transition from antiferroelectric phase to another one.

We investigated the dielectric properties for La0.53Na0.41-xLixTiO3 (x < 0.26). The temperature dependence of the dielectric constant for x = 0.00 shows the quantum paraelectric behavior. For other compounds, however, the anomalies caused by the jumps of Li ions between the off-center potions in the A-site and between A-sites were observed on the temperature dependence of the dielectric properties. (C) 2002 Elsevier Science B.V. All rights reserved.

Mg2+ ion-exchange with the Li+ ion in a fast Li ion-conducting perovskite La0.55Li0.35TiO3 was successful using MgCl2-KCl molten salt. The lattice parameter decreased as a result of the ion-exchange. These results suggest that the driving force of the ion-exchange reaction depends primarily on a decrease in the lattice energy, accompanied by the substitution of the smaller Mg2+ for the larger Li+ ion. A polycrystalline, ion-exchanged sample was found to show considerable Mg2+-ion conductivity (4.1 X 10(-6) S cm(-1)) at a lower temperature, 285degreesC, than the synthesis temperature, 450degreesC.

We executed a molecular dynamics simulation for the perovskite-type high Li ion conductor, La0.6Li0.2TiO3, using two different potential models, the fully ionic model (FIM) and the partially ionic model (PIM). Good reproducibility of the physical properties was obtained for the simulation using the PIM. While displacement of the Li ion from the A-site was indicated in both models, Li ion diffusion was observed only for the PIM below 600 K. These results suggest that the introduction of a small mobile ion into the A-site does not always induce high ion conduction and that the covalent character of the Ti-O bond is indispensable to the high Li ion conduction. The ionic conductivity, however, could not reproduce quantitatively in this simulation due to the random distribution of A-site ions in the simulation cell.

The lithium ion conductivities of perovskite-type oxide La-0.52(1) (Li0.30(1)TiO2.93(2))-Li-6 and La-0.52(1) Li-7(0.30(1)) TiO2.93(2) single crystals, sigma(6) and sigma(7), which were prepared by reproducible isotope exchange process using molten salt, were measured. The sigma(6)/sigma(7) ratio was almost the same as the classical theoretical value, 1.08, and the activation energies of these samples were constant. (C) 2002 The Electrochemical Society.

The crystal structure of a lithium ion-conducting perovskite La0.62(2)Li0.16(1)TiO3.01(3) obtained by furnace-cooling was refined by the Rietveld method using neutron-diffraction data at room temperature and 77 K. The adopted space group was Cmmm (No. 65). The anti-phased tilts of TiO6 octahedra along the b-axis in addition to alternative arrangement of La ions along the c-axis was confirmed. The position of Li was refined to be off-centered and in two equivalent positions in an A-site. The obtained structural information implies that the lithium ion conduction among A-sites occurs in the vicinity of La-poor layers two-dimensionally rather than three-dimensionally in this compound. (C) 2002 Elsevier Science (USA).

Dielectric properties of Sr1-xBaxTiO3 (x less than or equal to 0.30) solid solution were studied by means of dielectric constant, DE loop, pyroelectricity measurements, and so on. A quantum paraelectric to quantum ferroelectric transition was observed for samples with a small amount of Ba content ( 0.005 less than or equal to x less than or equal to 0.10). Possible phase transition mechanisms are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.

Based on the two-particle harmonic oscillator treatments for TO-modes in perovskite titanates ATiO(3), we proposed an estimation method of the total TO-amplitude and the excess TO-amplitude delta(TO) caused by mass-inequalities in TO-modes. Supposing that this excess TO-amplitude raises the internal energy of the ATiO(3)-lattice by an amount (1/2)C*delta(TO)(2), we got a linear correlation T-C versus delta(TO)(2) for ferroelectric perovskite titanates PbTiO3, BaTiO3 and 93%O-18-substituted (SrTiO3)-O-18.

A polycrystalline perovskite-type oxide Bi1/2Ag1/2TiO3 was synthesized under oxidizing condition generated by the decomposition of Ag2O. The lattice parameter a(0)=0.3889(2) nm assuming cubic symmetry. The temperature dependence of dielectric constant and the polarization curve suggested that Bi1/2Ag1/2TiO3 is ferroelectric.

Thin films of La1/2Na1/2TiO3 fabricated by pulsed laser deposition show interesting dielectric properties exhibiting quantum paraelectric-type temperature-insensitive dielectric constant below 50 K. The dielectric constant (epsilon(r)similar to 180) is also very stable under electric bias up to 4x10(4) V/cm. These properties indicate that these films coupled with high temperature superconductors have a great potential for microwave applications. (C) 2000 American Institute of Physics. [S0021-8979(00)07618-0].

We have tried to modify the low-temperature quantum paraelectric state of SrTiO3 by small amount of A-site doping. Investigation of the dielectric properties of D0.001Sr0.99TiO3 (D = Li, Ba, Ca, Mg, La, Y, Sm) polycrystalline samples showed that isovalent and heterovalent substitutions have different effects on the dielectric behavior. It is found that not only the atomic radius of dopant D but also oxygen vacancies and A-site vacancies determine the low-temperature states of the samples. (C) 2000 Elsevier Science B.V. All rights reserved.

Lithium Ion Conductivity in A-site Deficient Perovskites, Sr<sub>0.5</sub>La<sub>0.05</sub>Li<sub>0.35</sub>□<sub>0.1</sub>Ti<sub>0.5</sub>Ta<sub>0.5</sub>O<sub>3</sub> and Sr<sub>0.35</sub>La<sub>0.15</sub>Li<sub>0.35</sub>□<sub>0.15</sub>Ti<sub>0.5</sub>Ta<sub>0.5</sub>O<sub>3</sub>

Crystal structures and magnetic properties of the B-site ordered perovskites Sr2NiWO6 and Sr2NiTeO6 were investigated. Powder X-ray diffraction analysis revealed that Sr2NiWO6 and Sr2NiTeO6 have the tetragonal structure of I4/m (No. 87) and the monoclinic structure of C2/m (No, 12-2), respectively. Magnetic measurement of Sr2NiWO6 and Sr2NiTeO6 revealed that antiferromagnetic transition appears at 54 and 35 K, respectively. Heat capacity measurement gave a different transition temperature of 28 K for Sr2NiTeO6. Analysis of the entropy of the three-dimensional antiferromagnetic transition revealed that local ordering of spins begins at higher temperatures of observed T-N, especially in Sr2NiTeO6. (C) 2000 Elsevier Science Ltd. All rights reserved.

Four cuprate perovskites with the general formula A(2)CuB'O-6 (A = Ba, Sr; B' = W, Te) were synthesized and the structural acid the magnetic properties were investigated. Among four samples, perovskite Ba2CuTeO6 was formed only under high pressure. All the samples were tetragonally distorted B-site ordered perovskite-type oxides with I4/m symmetry. The CuO6 octahedra is elongated by the Jahn-Teller effect of Cu2+ ion and CuO6, and WO, (or TeO6,) octahedra rotates about the [001] direction, These compounds show two-dimensional antiferromagnetic behavior, because of the superexchange interaction between Cu2+ ions via an array of nonmagnetic ions, O-W-O (or O-Te-O) in the ab-plane perpendicular to the c-axis. The detailed analysis of the crystal structure made clear that the strength of the superexchange interaction depends more on the bond angle Cu-O-W (or Cu-O-Te) than the distance between Cu2+ ions in the abplane. (C) 1999 Academic Press.

The recovery of lithium ions by electrolysis using lithium ion conductive perovskite-type oxides La(2/3 - x)Li(3x)square(1/3 - 2x)TiO(3), as a separator, has been carried out. It was confirmed that La(2/3 - x)Li(3x)square(1/3 - 2x)TiO(3) has the selective permeability for lithium ions, and La(2/3 - x)Li(3x)square(1/3 - 2x)TiO(3) can be applied to the electrochemical recovery for Lithium ions. Moreover, Li-6 ion was recovered in preference to Li-7 ion by this electrolysis. This indicates the possibility of isotope separation for the lithium, Li-6 and Li-7. (C) 1999 Elsevier Science B.V. All rights reserved.

Molecular dynamics (MD) simulation was carried out on the high Li ion conductor, La0.6Li0.2TiO3:, using the partially ionic model (PIM). MD simulation of the Li ion conductivity with the variation of mobile ion size under high pressure revealed that this compound had the optimum lattice size for Li ion conduction and that the skeletal lattice was too small for Li+ ion to show the highest conductivity.

Ferroelectricity was induced in SrTiO3 by the isotope exchange of O-18 for O-16, Dielectric measurements confirmed the ferroelectricity of (SrTiO3)-O-18, showing a peak at 23 K. A hysteresis loop in the D vs E measurement and TO phonon observed in the Raman spectra supported the evolution of ferroelectricity in (SrTiO3)-O-18. This is the first demonstration of SrTiO3 becoming fen ferroelectric without the application of external fields or the introduction of a random field through cation substitution.

Novel perovskite-type oxide (La0.54(9)Ag0.33(1))TiO2.98(9) was synthesized by the conventional solid state reaction method. The perovskite-phase was found to have a simple cubic symmetry with the lattice parameter a = 3.8799(6) Angstrom. Using the adjusted solution of the sulfuric acid added some ammonium sulfates, the sample can be dissolved. The analysis of ICP was carried out to determine the elemental ratio of sample. At low temperature, (La0.54(9)Ag0.33(1))TiO2.98(9) Shows a quantum paraelectric behavior.

We have prepared new perovskite-type lithium ion conductors, LaxMyLi1-3x-yNbO3 (M = Ag and Na) and investigated the lithium ion conductivity in these compounds. Maximum lithium ion conductivity at 300 K was found to be 3.9 x 10(-5) 8 . cm(-1) for La0.25Ag0.20Li0.05NbO3, which contain the minimum amount of Li ion among these compounds. This result indicates that the Li ion conductivity of these compounds is mainly dominated by the activation energy. The reason for low ionic conductivities of these compounds is that the lattice parameters are not sufficiently optimized for Li ion conduction in the perovskite niobate. (C) 1998 Elsevier Science B.V. All rights reserved.

The (1 - x)LaAlO3-xSrTiO(3) solid solution system with the perovskite structure was synthesized and its dielectric behavior was investigated. The lattice parameter of (1 - x)LaAlO3-xSrTiO(3) increases with increasing the fraction of SrTiO3 in the system. 0.45LaAlO(3)-0.55SrTiO(3) shows a dielectric constant epsilon of 34, a temperature coefficient of resonant frequency rf of -8 ppmK(-1) and a dielectric loss e of 6900, which satisfy the suggested requirements for applications to mobile communications devices. The annihilation of the ferroelectric mode of SrTiO3 corresponds to the drastic decrease of epsilon and tau(f) of SrTiO3 to those of 0.25LaAlO(3)-0.75SrTiO(3).

The defective layered structure of the oxide RbLaSrNb2CuO9 was transformed into the three-dimensional perovskite under high pressure (5 GPa). (RbLaSrNb2MO9)-O-II (M = Mg and Zn) prepared under high pressure could be also added to the growing list of perovskite-related phases.

The novel perovskite-type oxides (Ln(1/2)Na(1/2))TiO3 (Ln = Dy, Ho, Er, Tm, Yb, Lu) were synthesized, and their crystal structures and dielectric properties were examined. (Ln(1/2)Na(1/2))TiO3 (Ln = Dy, Ho, Er, Tm, Yb, Lu) possess an orthorhombic symmetry with space group Pnma similar to (Ln(1/2)Na(1/2))TiO3 (Ln = Pr, Nd, Sm, Eu, Gd and Tb). Their lattice parameters and dielectric constants decrease with an increase in the atomic number of Ln (Ln = Dy to Lu). At low temperatures, (Ln(1/2)Na(1/2))TiO3 (Ln = Dy, Ho, Er, Tm, Yb, Lu) shows quantum paraelectric behavior. (C) 1998 Elsevier Science B.V. All rights reserved.

High-temperature quantum paraelectricity in perovskite titanate series (Ln(1/2)Na(1/2))TiO3 has been investigated in relation to their structural deformation for Ln(3+)-substitutions, Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Except for Ln = La and Ce, (Ln(1/2)Na(1/2))TiO3 has an orthorhombic unit cell with space group Pnma. The essential deformation parameter which lowers the highest dielectric constant epsilon(a) at the quantum paraelectric state, is found to be the average tilt angle delta among the neighboring [TiO6]-octahedra for (Ln(1/2)Na(1/2))TiO3. epsilon(a) decreases moderately as a function of cos(delta/2) for less than half-filled Ln(3+)-range, however, it decreases sharply for more than half-filled Ln(3+)-range. Supposing a virtual spontaneous polarization P-s with a virtual ferroelectric transition temperature T-o, and a zero-point vibrational energy hvo/2 of Ti4+-oscillators in [TiO6]-octahedra, a condition for the appearance of quantum paraelectricity in perovskite titanates is given by T-o < T* similar to hv(o)/2k, where T* is the cross-over temperature from classical to quantum regime. By analogy with the simple harmonic oscillator, the width of the potential on the Ti4+ ions in [TiO6]-octahedra determines their zero-point energy hv(o)/2, which is considered as the quantum fluctuation energy, replaces the thermal fluctuation energy kT below the cross-over temperature T*. The fundamental frequency v(o) of the Ti4+-oscillator is characteristic of the materials, that is, the narrower the potential is, the higher the v(o) is. Therefore, the structural deformations through the tilts or shrinks of the [TiO6]-octahedra cause to the high-temperature quantum paraelectricity in the perovskite titanates via increase in v(o). T* and T-a, the arrival temperature at the quantum paraelectric state. (C) 1998 Elsevier Science B.V. All rights reserved.

The average mass of A ions m(A) in nonconductive perovskite titanates ATiO(3) and (A(1/2)' A(1/2)") TiO3 is found to be a good criterion which discriminates the 5 kinds of ferroelectrics (m(A) > 100 a.u.) from the 17 kinds of quantum paraelectrics (m(A) < 100 a.u.). The results denote that Last's mode A-TiO3 in the three ferroelectric soft modes in cubic ATiO3 is responsible to the appearance of ferroelectricity in perovskite titanates. Discussions of the effect of the mass-inequality on the amplitudes of the component particles in the two-particle simple harmonic oscillator are given concerned with Last's mode.

The behavior of a high temperature quantum paraelectricity was discovered in perovskite-type titanates (Ln(1/2)Na(1/2)) TiO3 (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu). They possess an orthorhombic symmetry with space group Pnma. All of these samples have a similar arrival temperature in the quantum paraelectric state (T-a similar to 40 K), and almost similar average Ti-O bond distances. Their dielectric constants are determined by the tilts among the neighboring [TiO6] octahedra. The tilts among the neighboring [TiO6] octahedra increase, and the dielectric constants decrease with increasing the atomic number of Ln(Ln = Pr to Lu).

The anomalous peak in dielectric constant versus temperature of perovskite CdTiO3 appears at 77 K, which corresponds to the nonlinear D-E hysteresis loop below 80 K. The powder X-ray diffraction profiles at room temperature and 15 K do not change evidently. The indices of the diffraction profiles satisfy the extinction rule of both centrosymmetric space group Pnma and noncentrosymmetric Pna2(1). In the case of profiles at 15 K, the R factors of Rietveld refinement by Pnma or Pna2(1) reveal nearly the same satisfactory values. No differences can be distinguished between the Raman spectra at room temperature and 4 K. Although X-ray diffraction profiles and Raman spectra can not provide any effective structural differences, the D-E hysteresis loop suggests that a transition from centrosymmetric space group Pnma to noncentrosymmetric Pna2(1) may exist.

Compressibility measurements for Bi2.2Sr1.8CaCu2O8+delta (Bi-2.2:1.8:1:2) and IBi2.2Sr1.8CaCu2O8+delta (IBi-2.2:1.8:1:2) single crystals were carried out in a diamond-anvil pressure cell up to 9 GPa. The values of bulk modulus are 68.56 and 48.21 Gpa for Bi-2.2:1.8:1:2 and for IBi-2.2:1.8:1:2 single crystals, respectively. Hall coefficients and resistivities for oxygen annealed Bi-2.2:1.8:1:2 and I0.7Bi-2.2:1.8:1:2 single crystals were measured under high pressure up to 1.5 GPa. The value of dR(H)/dP for the oxygen annealed crystal is -0.06 x 10(-3) cm(3) C-1 GPa(-1), which is one third of the as-grown crystal. The decrease of dR(H)/dP after oxygen annealing is considered to be due to the increase of homogeneity of oxygen during high temperature annealing, The dR(H)/dP of I0.7Bi-2.2:1.8:1:2 is -0.39 x 10(-3) cm(3) C-1 GPa(-1), which is nearly the same as that of IBi-2.2:1.8:1:2. That the negative dR(H)/dP of intercalated crystals is nearly twice as large as that of pristine crystals is concerned with the deposition of the iodine molecular state under pressure. The T-c of oxygen-annealed Bi-2.2:1.8:1:2 increases with increasing pressure at a parabolic curve below 1.5 Cpa. By using the Gupta model, we simulated T-c(P) up to 6 GPa, and found that the maximum value of T-c(P) is 88 K at P = 4.1 GPa. This is in good agreement with the experimental result measured by Klotz et al. [Physica C 209 (1993) 499]. The T-c of the I0.7Bi-2.2:1.8:1:2 crystal increased linearly at a rate of dT(c)/dP = 3.5 K/GPa. This is the opposite of the behaviour of IBi-2.2:1.8:1:2 which decreased linearly at a rate of dT(c)/dP = -3.6 K/GPa, although both intercalated crystals are overdoped compounds. (C) 1997 Elsevier Science B.V.

A perovskite La0.59+/-0.01Li0.27+/-0.01TiO3.02+/-0.02 single crystal was grown by the floating zone method and its lithium ion conductivity was measured. The conductivity was found to be predominantly ionic. The ionic conductivities at 300 K parallel and perpendicular to the c-axis are 5.8 x 10(-4) and 6.8 x 10(-4) S.cm(-1), respectively. The anisotropy of the ionic conductivity corresponds to that of the structure, i.e., of the distribution of La ions. Furthermore, the ionic conductivity and activation energy for ion conduction are almost the same as those of a grain in polycrystalline samples, indicating that the evaluation of the ionic conductivity of polycrystalline samples was appropriate.

The effect of substitution and hydrostatic pressure on lithium ion conductivity in polycrystalline Ln(1/2)Li(1/2)TiO(3) (Ln = La, Pr, Nd and Sm) were investigated and the ion conduction mechanism in perovskite-type oxides was elucidated. The lithium ion conductivity was found to decrease, accompanied by an increase of the activation energy and volume for the ion conduction when the ionic radius of Ln ions was decreased or high pressure was applied for these compounds. A simple energetic calculation using a two-body central force has confirmed the importance of the bottle-neck size for ion conduction, which effectively determines the value of the repulsion potential between oxygen and lithium ions. (C) 1997 Elsevier Science Ltd.

A detailed study of annealing and pressure effects on structural phase-transition temperature (T-s) and ferromagnetic transition temperature (T-c) was investigated for single crystal La0.85Sr0.15MnO3. T-s and T-c, respectively, decrease and increase with increasing pressure and annealing time, which indicated that the lattice distortion is relaxed and the double-exchange interaction is enhanced by annealing and pressure. Three states, orthorhombic phase state, orthorhombic and rhombohedral phases coexisting state, and rhombohedral phase state, can be induced by controlling annealing time at high temperature and by hydrostatic pressure. Tn the La0.85Sr0.15MnO3 compound, T-c was found to increase about 15 K when the orthorhombic phase transforms to the rhombohedral phase.

A detailed study of annealing and pressure effects on structural phase-transition temperature ((Formula presented)) and ferromagnetic transition temperature ((Formula presented)) was investigated for single crystal (Formula presented)(Formula presented)(Formula presented). (Formula presented) and (Formula presented), respectively, decrease and increase with increasing pressure and annealing time, which indicated that the lattice distortion is relaxed and the double-exchange interaction is enhanced by annealing and pressure. Three states, orthorhombic phase state, orthorhombic and rhombohedral phases coexisting state, and rhombohedral phase state, can be induced by controlling annealing time at high temperature and by hydrostatic pressure. In the (Formula presented)(Formula presented)(Formula presented) compound, (Formula presented) was found to increase about 15 K when the orthorhombic phase transforms to the rhombohedral phase. © 1997 The American Physical Society.

The La3+ ion of a quantum paraelectric perovskite La1/2Na1/2TiO3 was substituted with the smaller tripositive lanthanide ions Ln(3+). The X-ray structural study and Rietveld refinement of Ln(1/2)Na(1/2)TiO(3) 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 Ln(1/2)Na(1/2)TiO(3) for Ln = La similar to Eu.

Dielectric properties of quantum paraelectric materials, SrTiO3, CaTiO3 and (La1/2Na1/2)TiO3, were presented and discussed since they show the titled dielectric properties in the lowest temperature range. In order to show our strategy to obtain the titled materials for microwave resonator applications, dielectric properties of several solid solution systems, SrTiO3-LaAlO3, Sr2TiO4-SrLaAlO4 and BaTiO3-Ba(Mg1/3Ta1/3)O-3 were exemplified. Concerning about relaxer ferroelectric materials, it is pointed out that a drastic broadening of ferroelectric phase transitions in the KNbO3-BaTiO3 and BaTiO3-Ba(Fe1/2Ta1/2)O-3 solid solution systems is caused by a strong local field fractuation come from the randomly oriented permanent electric dipoles produced by the heterogeneous cationic charge distribution in the solid solution.

Hall coefficients and resistivities have been measured on oxygen-annealed Bi2.2Sr1.8CaCu2O8+y single crystals under hydrostatic pressure up to 1.6 GPa and the results are compared with those on as-grown and iodine-intercalated ones. Under pressure, the Hall coefficient of the oxygen-annealed crystal decreases and the pressure derivative of the Hall coefficient is - 0.12 x 10(-3) cm(3)C(-1)GPa(-1). The variation of T-c, contrary to the iodine-intercalated crystal, shows a linear increase at the rate of dT(c)/dP = 2.3 K GPa(-1), whereas the Hall coefficient at ambient pressure is 2.15 x 10(-3) cm(3)C(-1), very close to the value of the iodine-intercalated one. The positive behavior of dT(c)/dP is an indication that the hole concentration in the CuO2 layers is located at the underdoped region and holes derived from extra oxygen are probable in other layers, e.g., Bi2O2 layers. The resistivities along the c-axis direction are semiconductor-like, indicating the holes from extra oxygen are two-dimensional.

Cooperative Interaction of Oxygen Octahedra for Dielectric Properties in the Perovskite-related Layered Compounds Sr<i><sub>n</sub></i><sub>+1</sub>Ti<i><sub>n</sub></i>O<sub>3<i>n</i>+1</sub>, Ca<i><sub>n</sub></i><sub>+1</sub>Ti<i><sub>n</sub></i>O<sub>3<i>n</i>+1</sub> and Sr<i><sub>n</sub></i><sub>+1</sub>(Ti<sub>0.5</sub>Sn<sub>0.5</sub>)<i><sub>n</sub></i>O<sub>3<i>n</i>+1</sub> (<i>n</i> =1, 2, 3 and ∞)