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The responses of perovskite ferroelectrics to the applied electric field, such as strains and electric displacements, are not proportional to the strength of electric field but generally show a non-linear behavior. This paper reviews previous studies on non-linear piezoelectric and dielectric responses mainly done by the author's research group. The mechanism generating non-linear responses is the domain-wall motion and the dipole fluctuation in the polar nano-regions of relaxors. Some experimental results of the electric-field induced strains of PZT ceramics and the non-linear dielectric behaviors of relaxors including dielectric used in multi-layered ceramic capacitors (MLCCs) are presented. The non-linear piezoelectric and dielectric behaviors of perovskite ferroelectrics are discussed to find the key issues for piezoelectric actuators and MLCCs used in future applications.

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(K, Na, Li)NbO3 (KNN) ceramics was reported to show excellent piezoelectric properties and has been regarded as a candidate of lead-free piezoelectric materials. However, the effects of hard additives on the properties have not been studied intensively so far. In this study, KNN ceramics with hard character dopants doped have been prepared by a solid state reaction and their electrical properties were examined.

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Dielectric and electromechanical properties of Ba(Ti_0.8Zr_0.2)O₃ ceramics were investigated. The Ba(Ti_0.8Zr_0.2)O3</SUB ceramics are prepared by conventional solid state reaction from the powder synthesized by spray drying. The powders are pressed and sintered at 1300-1500C. With increasing sintering temperature, the relative density and dielectric constant of the samples increase, generally. BTZ ceramics sintered at 1350C exhibit the dielectric constant of 5840 and loss tangent of 0.006 at room temperature. The Ba rich samples are hard to be sintered relatively and exhibit lower dielectric constant and higher loss tangent.

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Almost impurity-free, defect-free and dense barium titanate (BaTiO3) nanoparticles with various sizes from 20 to 430 nm were prepared using the 2-step thermal decomposition method. The crystal structures of these particles were investigated using a synchrotron radiation X-ray diffraction method. The observed diffraction pattern was analyzed using a new particle structure model. As a result, it is found that the BaTiO3 nanoparticles have composite structures composed of (a) tetragonal core, (b) gradient lattice strain layer and (c) cubic surface layer. Despite particle sizes, lattice parameters of tetragonal core and cubic surface layer were almost constant. The dielectric constant of BaTiO3 particle was estimated on basis of the new composite model, and the size effect for BaTiO3 nanoparticles was explained.

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Ba(Sr,Ti)O3 (BST) dielectric films were deposited by rf magnetron sputtering because of interest of their microwave integrated circuit applications. The dependences of crystallinity and electrical properties of the films on sputtering conditions were investigated. Epitaxial BST films can be obtained on MgO and sapphire substrates at substrate temperature of 650oC. The crystallinity of films obtained depend on oxygen partial pressure in sputtering gas revealing that their electrical properties were improved at low partial pressure.

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This study investigates the effect of doping on the electrical properties of BST thin film capacitors. BST thin films were deposited by an RF magnetron sputtering technique on Si wafers. BST films were prepared with Y concentration of 0-5%. Lattice parameters were measured using synchrotron radiation and the zero strain state of the film for each composition determined from X-ray analysis. The results show that the film strain state strongly depends on Y composition with tunability decreasing with increasing tensile strain. Mechanisms for the observed changes in permittivity, tunability due to doping will be discussed.

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The electrooptic properties and the site occupancies of La ions in La-substituted Pb(Zr_0.65,Ti_0.35)O₃ films, hereafter La-PZT films, were investigated. The La-PZT films with La-contents ranging from 0 to 12% were prepared on (111)Pt/Ti/SiO₂/(100)Si substrates by Chemical solution deposition (CSD). The electrooptic property of the films was evaluated using a photospectroscope. Site occupation was determined by Raman spectroscopy. As a result, it is found that the resonant wavelength shift by applying DC bias voltage is maximum in the La-PZT film with a La content of 0%, not 8-9%, and La ions were also substituted for B-site at La-contents over 3% while La ions were selectively substituted only for A-site up to the La-content of 3% in our films.

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Recently, Effect of the residual stress in ferroelectric thin films has been focused because the residual stress affects electrical properties of the resultant films. Basically, phase transition and difference of thermal expansion coefficient between electrode and PZT thin film are the main origin for residual stress in the resultant films. Therefor in this study, we prepared PZT thin films and discussed the effect of crystal orientation in PZT thin film on the residual stress by Raman scattering spectroscopy. As a result, increasing c-axis orientation ascribed to the increased residual stress in films.

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In this study, we investigated the effect of plasma for low-temperature crystallization of Pb(Zr,Ti)O ₃ (PZT hereafter) thin films on SrTiO₃ seeds by plasma enhanced metalorganic chemical vapor deposition (PECVD). From the previous study, we found that the slow deposition rate of PZT film is critical factor for low-temperature crystallization of PZT films on SrTiO₃ seeds. To investigate the mechanism of low-temperature crystallization mechanism, it is necessary to investigate the source decompositions of MO sources for PZT film. The RF plasma is one of useful method for decomposition of MO sources at low-temperature. In-situ and ATR-FT-IR were used for observation of decomposition of MO sources during PZT deposition and final PZT films, respectively. The details of this study is still under investigation.

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ZnO-based thermoelectric oxide (Zn0.98Al0.02O) with nanoporous (nanovoid) structure was investigated in terms of the preparative conditions of the nanovoids by using monodisperse polymethylmethacrylate (PMMA) particles of 150, 425, and 1800 nm in average diameter as a void forming agent.The thermal conductivity of the samples with the PMMA particles of 5 – 7 wt% efficiently decreased with keeping the electrical performance almost intact, resulting in the larger Z values for the smaller PMMA amount.

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The highly c-axis oriented Al doped ZnO was prepared by a combination of high magnetic field and gelcasting techniques. Optimized gelcasting conditions made it possible to align the particles preferentially along the c-axis within a short exposure time in the high magnetic field. The particle orientation was not degraded and disturbed by the gelation and subsequent processing. The degree of orientation was increased after sintering at 1400oC. This study indicated that applying the magnetic alignment via gelcasting method provides effective and versatile techniques to fabricate large and dense grain oriented materials.

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Sr-Ru-O in various of Ru to Sr (R_Ru/Sr from 0.5 to 1.4) were prepared by spark plasma sintering (SPS) and the effect of composition on the Seebeck coefficient, electrical conductivity and thermal conductivity were investigated. All compositions had dense body around 90-100% of theoretical density. SrRuO₃ and Sr₂RuO₄ in a single phase were obtained at R_Ru/Sr=1.0 and 0.5, respectively. The second phases of RuO₂, Ru and Sr₃Ru₂O₇, Sr₂RuO₄ were identified at R_Ru/Sr>1.0 and R_Ru/Sr<1.0, respectively. The electrical conductivity increased with increasing R_Ru/Sr at room temperature and exhibited metallic-like behavior for all samples except the semiconducting behavior at R_Ru/Sr=0.5. The Seebeck coefficient was around 20-40 microVK^-1 independent of composition and temperature at R_Ru/Sr 0.7. Thermal conductivity was around 2-7 Wm^-1K^-1 at room temperature and slightly increased with increasing temperature and Ru/Sr.

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Reaction bonding and post sintering process were applied to fabricate SiAlON ceramics added with ZrO₂ to clarify the effect of ZrO₂ addition on nitridation behaviour and phase composition of the sintered ceramics. Added ZrO₂ was transformed to ZrN phase after reaction bonding process and then re-transformed to ZrO₂ phase at the post sintering process.

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The fracture resistance curve and Hertzian contact fatigue test of TiN particle dispersed Si3N4 ceramics were carried out. The Si3N4 ceramics without TiN showed a typical R-curve, that is the KR was initially around 5.5 MPam1/2, it increased during fracture and it achieved 6.5MPam1/2 at the crack extension of 300m. On the other hand, Si3N4 ceramics with TiN particles has higher initial KR value and their R-curve indicated less slop than that without TiN. Although the strength of the Si3N4 ceramics without TiN degraded after cyclic indentation, that of TiN particle dispersed Si3N4 ceramics maintained because of limited crack generation and extension. The cyclic contact fatigue was explained by the difference in R-curve behavior.

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SiC/BN nanocomposite powders were produced by heating the starting materials of boric acid, silica and carbon powders in nitrogen atmosphare. At 800 degree C, borosilicate glass was formed by reaction of boric acid with silica, and a SiC/BN nanocomposite powder was synthesized by carbothermal reduction and nitridation of borosilicate glass over at 1550 degree C. The SiC/BN composites sintered by hot-pressing the nanocomposite powders showed high strength and good machinability.

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