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Strontium titanate is a model quantum paraelectric in which in the region of dominating quantum statistics the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero-point motion contribution. The enhancement of atomic masses by the substitution of 18O for 16O decreases the zero-point atomic motion and low-T ferroelectricity in SrTi18O3 is realized. In this study we report on the local structure of Ti in SrTi16O3 and SrTi18O3 by Ti K-edge extended x-ray absorption fine structure measurements in temperature range 6 – 300 K.

The average structure and microstructure of a lithium-ion conducting perovskite La2/3−xLi3xTiO3 (x = 0.12) were investigated using neutron diffraction and transmission electron microscopy (TEM). The obtained results were compared with those of previous studies on La2/3−xLi3xTiO3 series compounds, and the relationship between their structures and ionic conduction was discussed. The Rietveld refinement using neutron diffraction data reveals that the average structure (space group: Cmmm) of furnace-cooled Li-rich La2/3−xLi3xTiO3 (x = 0.12) involves alternative ordered arrangement of La along the c-axis and anti-phase-tilt of TiO6 octahedra along the b-axis as with Li-poor La2/3−xLi3xTiO3(x = 0.05). It was found that the strong correlation between structure and percolative diffusion pathways in the perovskites is primarily referred to the ordered arrangement of La ions, and the “bottleneck” square—surrounded by four oxygen ions determined by the distortion and tilt of TiO6 octahedra. In addition, the 90°-oriented micro-domain structure, which also influences the percolative diffusion pathways in La2/3−xLi3xTiO3, was observed by TEM.

We have performed high field magnetization measurements on the quasi onedimensional (1D) antiferromagnet BaCo2V2O8, which shows a curious field-induced orderdisorder transition, in pulsed magnetic fields up to 55 T. The observed magnetization curves up to the saturation field show non-linear increases, suggesting a strong quantum fluctuation. We analyze the magnetization curves in terms of the S = 1/2 1D XXZ model.

We report the investigation of frequency dependence of dielectric responses of lead magnesium niobate (PMN) in the range from 1 mHz to 10 MHz at various temperatures (200 K–350 K). Three relaxations were obsereved in PMN single crystal, one at high frequency, one at intermediate frequency, and one at low frequency. The high frequency relaxation falls into the frequency range over 1 MHz. The spectral width of the intermediate frequency (range from ∼ 1 Hz to ∼ 1 MHz) relaxation, which dominates the dielectric behaviors in the so-called “diffuse phase transition” region (260 K–280 K), broadens rapidly at about 270 K, and is almost independent on temperature for T < 260 K. These facts are not in agreement ith the glass freezing picture. The low frequency relaxation shows an Arrhenius-type behavior with barrier height of 0.38 ± 0.01 eV.

Parallel capacitors of BaxSr1–xTiO3 (x = 0.01 and 0.05) were fabricated, and their characteristics as a capacitance thermometer were investigated. The dimensionless temperature sensitivities at 2.5 K for x = 0.01 and 0.05 were found to be 0.041 and 0.026, respectively. Particularly, the value for a capacitor with x = 0.01 is five times larger than those of commercially available ferroelectric doped SrTiO3 capacitance thermometers. These results reveal that a parallel-plate capacitor using quantum ferroelectric BaxSr1–xTiO3 has a potential application as a capacitance thermometer for monitoring cryogenic temperatures in a high magnetic field. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermometric properties of the capacitance temperature sensor with polycrystalline (Sr1−x Cax)TiO3 (x = 0.05) have been investigated at cryogenic temperatures. Ferroelectric state appeared at 31.8 K due to Ca doping. Temperature sensitivity S and dimensionless temperature sensitivity Sd at 2.5 K were 90 pF/K and 0.045, respectively. This capacitance temperature sensor could improve the accuracy of temperature sensing at cryogenic temperatures due to its large dimensionless temperature sensitivity.

An effective method of synthesis of tin phosphide Sn{sub 4}P{sub 3} starting from metallic tin and amorphous red phosphorus by a low-temperature (200 {sup o}C) solvothermal reaction in ethylenediamine is offered. The key parameters of this process - duration, temperature, and the ratio of initial components (Sn/P) are studied. The structure, phase composition, and morphology of the products are investigated using powder X-ray diffraction and scanning electron microscopy. Different synthetic ways for tin phosphide are discussed and compared with the proposed one. The mechanism of solvothermal preparation of tin phosphide in ethylenediamine is discussed. It is shown that the proposed solvothermal method opens up the possibility of preparing other metal-rich phosphides. - Graphical abstract: SEM microphotograph of the sample of layered tin phosphide Sn{sub 4}P{sub 3}, which can be simply solvothermally synthesized from metallic tin and red phosphorus.

To elucidate mechanisms responsible for the enhanced piezoelectric properties in the potassium-sodium niobate-based solid solutions, phase diagram of the (1 − x) (Na0.5K0.5)NbO3-xATiO3 (A = Sr, Ba, and Pb) systems has been established according to the dielectric constant measurement and the crystal structure analysis results. A tetragonal/orthorhombic morphotropic phase boundary (MPB) is found around x∼ 0.05, where the piezoelectric properties were enhanced. Rietveld refinements show that the tetragonal/orthorhombic MPB is the same as that found in the lead zinc niobate-lead titanate system.

We report on the growth condition and magnetic properties of SrCo 2 V 2 O 8 crystal. High-quality single crystals with dimensions 3×3×6 mm 3 have been successfully grown from its stoichiometrical melt in air by spontaneous nucleation method. Preliminary magnetic measurements show large canted ferromagnetism and unusual paramagnetic anisotropy of the grown crystals.

Vacancies have been introduced to the perovskite A- and B-site to study their effects on the dielectric and the piezoelectric properties of the (Na 0.5 K 0.5 )NbO 3 -SrTiO 3 solid solution. It is found that, rather different from in the case of PZT ceramics, both A- and B-site vacancies do not soften piezoelectric properties of (Na 0.5 K 0.5 )NbO 3 -SrTiO 3 solid solution.

A 2-mm-diameter glass sphere of ferroelectric BaTi2O5 was fabricated from melt using containerless processing. The glass structure was analyzed by high-energy X-ray diffraction using an incident ph...

Magnetic properties of peculiar structural-type borate Cu 2 NiB 2 O 6 are investigated by means of ac susceptibility, dc magnetization, and heat capacity measurements. This material is isostructural to Cu 2 CoB 2 O 6 , of which the structural configuration is composed of quasi-one-dimensional six-columns ribbons. Our experimental results show that this material displays an antiferromagnetic phase transition at ∼15 K, which differs from Cu 2 CoB 2 O 6 showing spin-glass behavior below 5 K. The different magnetic ground states in these compounds may be attributed mainly to the subtle balance of the exchange energy in the scalene triangles.

The parallel capacitors of YBa 2 Cu 3 O 7 −δ/SrTiO 3 /YBa 2 Cu 3 O 7 −δ for SrTiO 3 with film thickness of 300 nm and 600 nm were fabricated by means of Pulsed Laser Deposition (PLD) and Chemical Mechanical Planarization (CMP) method. In order to investigate the polarization mechanism in the SrTiO 3 films, the frequency dispersions of dielectric constant and tan δ were studied. For 600 nm SrTiO 3 film, the dielectric frequency dispersion occurred at frequency above 10 5 Hz and tan δ at 1 kHz and 10 kHz are 0.001 and 0.015, respectively. These results revealed that the oxygen deficiency in the SrTiO 3 crystals is very small and polarization mechanism is dominated by dipoles polarization.

Properties and the crystal structures of novel complex oxides were introduced based on the recent experimental results of the author's group. Results of lithium ion conductor, ferroelectrics, magnetic conductor, and quasi-one-dimensional magnet were explained from the viewpoints of the structure and the chemical bond.

Magnetic properties of BaCu2V2O8 single crystals obtained by the spontaneous nucleation method using V2O5 as a self-flux are investigated. Singlet ground states with spin gaps of 215 and 223 K are observed along the directions parallel and perpendicular to the c-axis of the crystal, respectively, being in good agreement with powder sample measurements. Reinvestigation of the crystal structure reveals that the whole structural framework of BaCu2V2O8 crystal can be described as an assembly of alternating chains, which are built by edge-sharing pairs of CuO4 square-plaquettes and VO4 tetrahedra along the c-axis. The magnetic nature of BaCu2V2O8 is well understood based on this structural interpretation.

The temperature dependences of the non-linearity coefficient and the third order susceptibility are investigated on crystals of ordinary (STO16) and oxygen isotope substituted (STO18) strontium titanate. The strong nonlinear dielectric response is described within the framework of a classic equation of state involving a non-linearity coefficient with non-classic temperature dependence after correction for a contribution due to random-field induced polar nanoregions. The temperature dependences of the third order susceptibility display a very sharp peak at the phase transition of STO18 and a monotonic increase for STO16 when temperature decreases, respectively.

A central peak (CP) has been found mainly in the VH light scattering spectra of SrTi(18 O 0.87 16 O 0.13)3 (87% 18O-exchanged SrTiO3). Both of the intensity and relaxation time of the CP show broad peaks around T m ≈ 22 K (below the transition temperature T c ≈ 25 K). The physical origin of the CP is determined not to be the polarization fluctuation, representing that this CP is not a sign of a phase transition of order-disorder type. The stochastic fluctuation of the spatial derivatives of the polarization would be the physical origin of the CP.

Some novel features of strontium titanate are presented. First, it reveals secondary ferroicity when exposed to an external electric field in its tetragonal paraelectric state. It is shown on isotopically doped SrTi 18 O 3 (STO18) that odd-oriented ferroelastic domains can be switched under anomalously large electrostriction such as to create a perfect axially orientated state. Second, the strong non-linear dielectric response of STO18 can be described within the frame of a classic equation of state involving a nonlinearity coefficient with non-classic temperature dependence after correction for a contribution to random-field induced polar nanoregions. Third, static nonzero-external field scaling analysis reveals a non-classic exponent a = δ/(δ −1) = 1.62 when respecting the validity of the quantum temperature concept in the vicinity of Tc≈25 K. Fourth, polarized microscopy confirms that the isotope-induced ferroelectric low temperature phase is probably triclinic rather than orthorhombic. This results fr...

We report the results of a neutron powder diffraction study of the La(0.62)Li(0.16)TiO3 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.

Due to its close-shelled electron configuration, perovskite structured oxide Cd 3 TeO 6 was originally regarded as an electric insulator. When Cd 3 TeO 6 was electron-doped by the substitution of trivalent cations (In 3+ , La 3+ and Bi 3+ ) and the introduction of oxygen vacancies, all samples showed bright changes on thermoelectric properties. A substantial negative temperature dependence of resistivity was observed in non-substituted Cd 3 TeO 6 , while substituted samples showed a slight dependence on temperature. Obviously resistivity degradation was found on air-sintered samples after nitrogen treatment. The negative Seebeck coefficient and Hall coefficient obtained indicated that electrons were the charge carriers. Among the three types of substituted cations, indium exerted the largest effect on the decrease of resistivity down to 1.3 mΩ cm at room temperature. The best thermoelectric power factor of 1.35 × 10 −4 W m −1 K −2 was obtained for Cd 2.97 In 0.03 TeO 6 at 300 K.

To study the factors affecting the dielectric and piezoelectric properties of bismuth-containing complex perovskites, the solid solution (1− x )Pb(Mg 1/3 Nb 2/3 )O 3 – x Bi(Mg 2/3 Nb 1/3 )O 3 was prepared by the solid state reaction method and its dielectric and piezoelectric properties were investigated. It is found that (1) at room temperature, the nonlinearity of the DE -loop for Pb(Mg 1/3 Nb 2/3 )O 3 is completely suppressed at a rather low x ( T d much higher than the dielectric constant peak temperature T m and T m − T d decreases considerably with increasing x ; and (3) frequency dispersion Δ T m = T m (1 MHz)− T m (10 kHz) increases with increasing x . Possible factors responsible for the variation of the dielectric and piezoelectric properties with x are discussed.

A parallel capacitor of epitaxially grown YBa 2 Cu 3 O 7− δ /SrTiO 3 /YBa 2 Cu 3 O 7− δ was fabricated by a chemical mechanical planarization method and its characteristics as a capacitance thermometer were investigated. The capacitance, temperature sensitivity, and dimensionless temperature sensitivity of the elements were found to be 1.7 nF, 10 pF/K, and 0.01 at 2.2 K, respectively. These values are of the same order as that of a commercially available bulk doped-SrTiO 3 capacitance temperature sensor. These results reveal that the parallel capacitor with quantum paraelectric SrTiO 3 film has potential for use in capacitance thermometers for monitoring cryogenic temperatures under high magnetic fields.

In an YBa 2 Cu 3 O 7− δ /SrTiO 3 /YBa 2 Cu 3 O 7− δ parallel capacitor fabricated by a chemical mechanical planarization method, the dielectric constant and loss in the presence of electric fields at 2.2 K were more than 26,000 and less than 0.027, respectively. We propose a multilayer model that explains this behavior. The model assumes that the SrTiO 3 film is composed of single-crystal-like SrTiO 3 layers with a dielectric constant e r = 30,000 and degraded SrTiO 3 layers with dielectric constants that vary continuously from 25, the dielectric constant of YBa 2 Cu 3 O 7− δ , to 30,000. Results of a numerical calculation revealed that the thickness of the single-crystal-like SrTiO 3 layer was more than 92% of a 600-nm-thick SrTiO 3 film.

The ferroelectric microregion (FMR) in quantum paraelectric SrTiO 3 is studied by Raman scattering using an optical cryostat with a 3 He refrigerator. By the partial exchange of the oxygen atom for its isotope 18 O, broad FMR spectra change drastically to underdamped Lorentzian-type spectra with decreasing temperature below 10 K. The peak is assigned to the ferroelectric soft Eu mode. The intense and sharp spectra of the Eu mode, which are nominally Raman inactive, indicate that the symmetry is lowered to a non-centrosymmetric symmetry in FMR. Furthermore, the softening characteristic of the soft Eu mode in a low-temperature region implies that the symmetry is not necessarily ferroelectric. The local symmetry breaking is enhanced by the substitution of the isotope 18 O.

Based on the hypothesis that long-term fetomaternal microchimerism is associated with acquired immunologic hyporesponsiveness to noninherited maternal antigens (NIMAs) or inherited paternal antigens (IPAs), several groups have recently reported successful cases of non-T-cell-depleted hematopoietic stem cell transplantation (SCT) from HLA-haploidentical family members mismatched for NIMAs. In this study, we examined the outcomes of 35 patients with advanced hematologic malignancies who underwent HLA-2-antigen- or HLA-3-antigen-incompatible SCT from a microchimeric NIMA-mismatched donor. After standard-intensity or reduced-intensity preparative regimens, all patients had sustained hematopoietic recovery with tacrolimus-based graft-versus-host disease (GVHD) prophylaxis. Grade II/IV acute GVHD occurred in 19 (56%) of 34 evaluable patients, while extensive chronic GVHD developed in 13 (57%) of 23 patients who could be evaluated. Multivariate analysis demonstrated that NIMA mismatch in the GVH direction was associated with a lower risk of severe grade III-IV acute GVHD when compared with IPA mismatch (P = .03). Fifteen patients were alive and 14 of them were disease-free with a median follow-up of 20 (range, 8 to 37) months. These results indicate that T cell-replete SCT from an HLA-haploidentical NIMA-mismatched donor can offer durable remission with an acceptable risk of GVHD in selected patients with advanced hematologic malignancies who lack immediate access to a conventional stem cell source.

CuCr 2 S 4 shows a p-type metallic conductivity and ferromagnetism with Curie temperatures T c of 375 K, and exhibit magnetic anomaly at 84 K (= T m ). CuCr 2 S 4 exhibits the coexistence of both the ferromagnetism and spin-glass with the irreversible magnetic effect below T m . The partial 20% Mg-substitution for Cu in CuCr 2 S 4 slightly reduces the T c and T m . Magnetorsistance of Mg x Cu 1− x Cr 2 S 4 can be expressed as Δ ρ = aH 2 − bH n below T m . a , b , and n are temperature-dependent adjustable parameters. These unique MR behavior would be attributed to the coexistence of the ferromagnetism and spin-glass-like order below T m . Mg-substitution decreased the conducting carrier, which forms the conduction band whose orbital motion gave the positive MR contribution. Therefore, Mg-substitution gave smaller positive MR contribution and consequently gave larger negative MR (maximum 7% at 10 K) in Mg 0.2 Cu 0.8 Cr 2 S 4 . These results suggest that Cr 3 d band filling control can be expected to give functional magnetoelectric transport properties in CuCr 2 S 4 .

Photoconductivity and various photo-magnetotransport properties have been studied in quantum paraelectric SrTiO3 crystals. SrTi16O3 shows giant photoconductivity, as reported before. The photodoped carrier in the 16O system is of electron type and has high mobility beyond 104 cm2 V-1 s-1 at 5 K. Its number can reach the order of 1015 cm-3. In contrast, isotope-substituted SrTi18O3 is not a good photoconductor. In addition, the photocarrier's mobility in the 18O sample is negligibly small. These results suggest a strong correlation between the quantum fluctuation and the giant photoconductivity in this quantum paraelectric system. In other words, the study of photocarrier dynamics is a novel approach to the investigation of quantum fluctuation in dielectric materials. 2004 The Physical Society of Japan

Optical second-harmonic generation (SHG) in SrTi16O3 (STO16) and SrTi18O3 (STO18) was investigated using the SHG microscope. While no-biased STO16 exhibits weak and almost temperature-independent SHG signals, a marked SHG is observed under the electric field in the quantum paraelectric region. In STO18, strong SHG signals appear spontaneously below 36K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, and STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar-order, the combined studies reveals that the long-range order of polar phase does not develop on the both crystals and is frozen in local regions.

The oxygen isotope exchange of 16O by 18O in SrTiO3 causes a drastic change from paraelectric to ferroelectric, due to the suppression of quantum fluctuation. The phase transition and origin of the huge domain wall response were evaluated by dielectric, magnetic (NMR), and optical measurements (SHG, light scattering). The results obtained corroborate (1) smeared ferroelectric transition at Tc due to quenched random field, (2) a quite large dielectric contribution from domain walls, (3) incomplete softening of the transverse optic mode, and (4) a large contribution from the relaxational mode to the phase transition. Quantitative explanations, given to individual results, may give hints to grasp the mechanism for the evolution of ferroelectricity, in which quantum fluctuation and random fields are dominant perturbations. Finally, some of the news studies on the SrTiO3 were also introduced.

Hyper-Raman scattering experiment has been performed in SrTi(18Ox 16O1-x)3 single crystal with exchange rate x = 0.87. A polar F1u Slater mode is detected in the cubic phase. This mode becomes an Eu mode in the tetragonal phase and softens toward the phase transition temperature Tc = 26 ± 3 K. Electric field induced light scattering experiment has also performed in SrTi(18Ox 16O1-x)3 single crystal with x = 0.96 under electric field of 120 kV/m. The softening behavior of the Eu mode (Raman-inactive mode) is observed clearly not only below Tc = 27 ± 1 K but also above Tc. However, the softening is confirmed to be incomplete (minimum frequency is about 200 GHz). These experimental facts strongly support the reported conclusion that the phase transition mechanism of SrTi(18Ox 16O1-x)3 is of displacive type (the instability of the Eu soft mode of Slater type causes the ferroelectric phase transition) but is not of ideal one.

The observation of A1-symmetry phonon-polariton of SrTi(18Ox 16O1-x)3 was carried out by impulsive stimulated Raman scattering with optical heterodyne detection. By the fit of the phonon-polariton dispersion relation, the static dielectric constant along the polar axis and the soft mode frequency were obtained at once. The present results well associated the previous Raman scattering and dielectric measurement study each other.

An optical birefringence study was carried out on the quantum ferroelectric phase transition in oxygen isotope exchanged system SrTi(16O1-x 18Ox)3. The ferroelectric ordering in (110)c and (001)c plates for x > 0.33 brought about a marked enhancement in the temperature dependence of birefringence. Tetragonal symmetry is considered to be broken into a lower symmetry, i.e. orthorhombic one, below Tc. The antiferrodistortive phase transition Ta was found to increase quadratically with an increase in temperature from 105 K for x = 0 to 108 K x = 1.0.

We report the Mn doping effect in FeCr2S4, which does not possess heterovalency, or static Jahn-Teller distortion, but exhibits large magnetoresistance. In order to see the effects of substituting Fe2+ for Mn2+ on the conduction, magnetism, and magnetoresistance, we carried out an experimental study of the electrical and magnetic properties of Fe0.5Mn0.5Cr2S4. FeCr2S4 has a spin-glass phase below 60 K ( = Tg) and a ferrimagnetic phase in the temperature range 60-170 K (Tc = about 170 K). In Fe0.5Mn0.5Cr2S4, both the spin-glass and ferrimagnetic transitions are observed in lower temperature regions (Tg = 45 K, Tc = 140 K). FeCr2S4 is a semiconductor, but exhibits metallic-like behavior in the temperature range 150-170 K. Fe0.5Mn0.5Cr2S4 does not exhibit such metallic behavior, but anomalous transition of the temperature dependence of resistivity is observed in the temperature range 100-180 K. Fe0.5Mn0.5Cr2S4 exhibits a larger maximum negative magnetoresistance (MR) than FeCr2S4. Thses experimental data can be well explained on the basis of the polaron model.

A photo-induced effect in the quantum dielectric system, such as SrTiO3, KTaO3, and CaTiO3, has been investigated under rather small external DC electric field. The dielectric measurement was performed under ultraviolet (UV) laser excitation combined with DC electric field. The gigantic photo-induced effects of dielectric properties of the quantum paraelectric systems have been firstly observed in the perovskite-type materials. The photoinduced dielectric effect was obtained as a function of DC electric field under constant UV irradiation.

Correlation between magnetic properties and Mn/Co atomic order in LaMn0.5Co0.5O3+δ was investigated by powder X-ray diffraction, dc magnetization, ac magnetic susceptibility, and heat capacity measurements. The Mn/Co atomic order was controlled by annealing at some temperatures and successive quenching. The qualitative and quantitative magnetic properties depend on whether the annealing temperature is above or below 1400 K. The samples annealed below 1400 K showed a clear heat capacity anomaly and deviation from Curie−Weiss law due to ferromagnetic critical fluctuation. On the other hand, the samples quenched from above 1400 K showed an unclear heat capacity anomaly, downward deviation from Curie−Weiss law, and asymmetric M−H loop after high-field cooling. These results suggest that the long-range ordering of the Mn/Co atomic configuration occurs at around 1400 K, that the long-range ferromagnetic ordering occurs only when the long-range order of Mn/Co atomic configuration is present, and that ferromagnet...

The relaxation phenomenon around 1300K in LaMn 0.5 Co 0.5 O 3+δ and their valence states of Mn and Co atoms were investigated by TG-DTA, powder X-ray diffraction, magnetic susceptibility, and XANES of two samples cooled at 10Kh -1 in the range 1673-973K and quenched from 1673K. DTA clarified that the relaxation phenomenon is not due to a first-order phase transition and that the temperature dependence of relaxation time is a thermal activation type, which suggests that the order-disorder phase transition of Mn/Co atomic ordering is second-order type. The results of lattice parameters, XANES, and magnetic susceptibility measurements suggest that the ground valence state of the ordered phase is Mn 4+ /Co 2+ and that a fraction of Mn 3+ /Co 3+ is increased either by disordering the Mn/Co atomic configuration or by increasing temperature.

A new perovskite compound Gd2MnTiO6 was synthesized and its crystal structure, magnetic and thermal properties have been investigated. The XRD patterns were refined by the Rietveld method and the refined lattice parameters with the monoclinic space group P21/n (No. 14) were a=0.5398 (2), b=0.5704 (2), c=0.7767 (2) nm and β=89.68 (2)°. The antiferromagnetic behavior was observed below 16.0 K and λ-type heat capacity was measured near this temperature.

A gigantic enhancement of dielectric constant by UV light irradiation is reported for the first time in the quantum paraelectric family of perovskite oxides, such as SrTiO 3 and KTaO 3 , under a weak DC field. The enhancement has not been observed in ferroelectric SrTi 18 O 3 induced by substitution of 18 O for 16 O. The present result suggests a new class of light-switching phenomena controllable externally.

Femtosecond time-domain observations of SrTi( 18 O x 16 O 1 m x ) 3 [STO18] in ferroelectric phase transition have been conducted by impulsive stimulated Raman scattering (ISRS). The phonon-polariton of A 1 -symmetry can be detected at the first time by the use of the heterodyne detection method with an optical phase mask. The static dielectric constant, which is calculated from the dispersion relation of the observed phonon-polariton, agrees well with the value reported in dielectric measurement. This fact indicates that the observed mode is the phonon-polariton originated from the coupling system between the ferroelectric soft mode and photon.

Marked field-induced second harmonic generation was observed in SrTi 16 O 3 at liquid He temperature. The intensity decreased towards 35K with the increase of temperature but it still remained significantly above 35K and gradually diminished and vanished around 100K. This indicates that ferroelectric nano-regions exist in higher temperature region and grow under electric field. On the other hand, 18 O-replaced SrTiO 3 (SrTi 18 O 3 ) exhibited SHG below 30K without electric field and the intensity decreased steeply above the temperature. This corresponds to the appearance of ferroelectric phase. The point group of field-induced phase of SrTi 16 O 3 and ferroelectric phase of SrTi 18 O 3 is orthorhombic mm 2 with polar axis along the cubic {110} direction.

Single-crystal X-ray diffraction measurements at low temperature were carried out using the image-plate technique in the vacuum chamber at BL02B1 of SPring-8. The intensity data were collected at 20 K, 70 K, and 150 K, 36 photographs being taken at each temperature. The systematic extinctions observed at 20 K could be summarized as h = 2 n + 1 for ( hk 0) reflections. This observation together with the observations of the ferroelectricity at this temperature uniquely determine the space group as P 2 1 ma though a previous report suggested the space group to be Pn 2 1 a . The structure could be refined with this space group yielding R = 0.056 for 4359 reflections. The structure of CdTiO 3 at 150 K was found to be almost identical to the previously reported one, belonging to the space group Pnma .

Dielectric properties of spark-plasma-sintered solid solution (1 m x )(Na 0.5 K 0.5 )NbO 3 m x PbTiO 3 were studied. Both the cubic-tetragonal and the tetragonal-orthorhombic phase transitions become more and more diffuse with increasing x . The strong deviation of the cubic-tetragonal phase transition temperature versus composition curve from the Vegard's law is observed. It is considered that (1) the introduction of heterovalence ions to both the perovskite A and B sites, and (2) the change of the mass difference between the perovskite B- and A-site, m B - m A, are two main factors responsible for the observations.

Raman spectra in SrTiO 3 single crystals were measured. In the ferroelectric phase below T c = 24 K in SrTi 18 O 3, two modes were observed to soften on heating towards T c = 24 K. These modes are assigned as the two split components of the ferroelectric soft E u -symmetry mode in the tetragonal phase above T c . The existence of the soft modes suggests that the ferroelectricity in SrTi 18 O 3 is intrinsic in nature. In SrTi 16 O 3, external electric field significantly increases the Raman intensity of the E u mode and induces the interaction with different symmetry modes. In the ferroelectric phase of SrTi 18 O 3, the electric field has much smaller influence on the soft modes.

The light scattering experiment has been performed in SrTi( 18 O x 16 O 1 m x ) 3 single crystal with the exchange rate of x = 0.86. The ferroelectric E u optical soft mode can be observed above the ferroelectric phase transition temperature T c , 27 K. It splits into two modes below T c . One of these two modes, which is supposed to be the A 1 (or B 2 ) mode, hardens with decrease in temperature. This experimental result implies that the phase transition of SrTi 18 O 3 is of the displacive type.

The gigantic photo-induced effect of dielectric property in the quantum dielectric material SrTiO 3 has been observed under rather small external DC electric field. The dielectric measurement was performed under UV laser excitation with energy above the band gap combined with a DC electric field. The photo-induced effect without a DC electric field has been enhanced with increasing of the AC electric field.

Oxygen isotope exchange for quantum paraelectric SrTiO 3 induces ferroelectricity whose T c is given by T c = 30.4(x - 0.33) 1/2 for SrTi( 16 O 1-x 18 O x ) 3 . Small frequency dispersion of e', large amplitude and bias dependences of e', polarization above T c for poled samples, and time relaxation of polarization below T c as well as the results of optical measurements by Raman, Brillouin and optical birefringence conclude that properties of oxygen-isotope exchanged strontium titanate resemble to those of Ca-doped samples, i.e., domain state. Difference between oxygen-isotope exchanged and Ca-doped strontium titanate was observed only in the pressure dependence of T c , which may be able to the difference in the random fields in the system.

In the search for high-performance piezoelectrics, (1-y)(Na0.5K0.5)NbO3–yPbTiO3 (y≤0.50) solid solution has been prepared using the spark-plasma-sintering method. Dielectric investigation reveals that both the ferroelectric phase transition temperatures and the peak value of the dielectric constant are strongly suppressed in the low y range. However, improved electromechanical coupling constants are observed at the same y range. These properties are explained by considering factors such as composition, crystal structure, ferroelectric domain microstructure, and poling conditions.

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 dielectric permittivity e′ - i\(\) of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In e′vs.T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.