Epitaxial tetragonal PZT films with (100)/(001) and (110)/(101) and (111) orientations were grown on various kinds of single crystal substrates having different thermal expansion coefficient. Volume fractions of (001) and (101) orientations in respective (100)/(001)- and (110)/(101)-oriented films were almost linearly increased with increasing thermal strain of the films that was generated under the cooling process after the deposition from the growth temperature to the Curie temperature. Perfectly (001)- and (101)-oriented films were grown on (111) CaF₂ substrates with large thermal expansion coefficient. Observed saturation polarization values linearly changed with the volume fractions of (100) and (101) orientations.

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The BiScO₃–PbTiO₃ binary system is known to have a morphotropic phase boundary (MPB) and a higher Curie temperature than Pb(Zr,Ti)O₃ and to exhibit excellent dielectric and ferroelectric properties. Perovskite BiScO₃–PbTiO₃ powders and thin films were synthesized via a chemical process using metal-organic precursor solutions. Homogeneous and stable precursor solutions, perovskite BiScO₃–PbTiO₃ single-phase powders and thin films on Pt/TiO_x/SiO₂/Si substrates were successfully prepared by optimizing the processing conditions. The 0.35BiScO₃–0.65PbTiO₃ composition was close to the MPB and had a Curie temperature of around 470°C. The electrical properties of BiScO₃–PbTiO₃ thin films showed a maximum at this composition. The dielectric permittivity of the 0.35BiScO₃–0.65PbTiO₃ thin film at the MPB was approximately 1700, with a dielectric loss tangent of less than 5% at room temperature. Furthermore, BiScO₃–PbTiO₃ thin films showed a typical ferroelectric polarization (P)–electric field (E) hysteresis loop. The remnant polarization (P_r) and coercive field (E_c) of the 0.35BiScO₃–0.65PbTiO₃ film were approximately 23 µC/cm² and 70 kV/cm, respectively.

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The Zr/Ti ratio dependence of refractive index and electrooptic coefficient of epitaxial (Pb,La)(Zr,Ti)O₃ (PLZT) films were investigated. PLZT films were fabricated on La-doped SrTiO₃ (La-STO) substrates by a chemical solution deposition (CSD) method. Optical properties in TE- and TM-modes were measured individually using a prism coupling method. The refractive indexes both in TE- and TM-modes were as large as that of the polycrystalline film, and increased with increasing Ti/(Zr + Ti) ratio. The refractive index in TE-mode was larger than that in TM-mode because the PLZT films received compressive stress from the La-STO substrates due to lattice mismatch. The refractive index in TM-mode almost linearly decreased with increasing applied an electric field while that in TE-mode slightly increased and saturated around at 200 kV/cm. The Pockels coefficient in TM-mode r₃₃ showed large change for compositions, while that in TE-mode r₁₃ showed little change. The maximum Pockels coefficient r_c of 156 pm/V was obtained for the epitaxial PLZT film with Ti/(Zr + Ti) ratio of 50%.

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Endurance properties of piezoelectric-induced longitudinal displacement for lead zirconate titanate (PZT) thick films were investigated to develop microelectromechanical systems (MEMS). A 5-µm-thick film was prepared using chemical solution deposition (CSD). Square and triangle waveforms and various frequencies of unipolar or bipolar electric fields were applied to the film. The effects of applied field switching cycles on the ferroelectric properties and longitudinal displacements were measured using a twin-laser interferometer system. Under the bipolar applied field switching condition, the remanent polarization and piezoelectric displacement decreased concomitantly with increasing applied field switching cycles, similar to fatigue behavior. The applied field switching waveform and frequency affect the fatigue profile. The piezoelectric displacement did not decrease when the unipolar square and triangle waveform were applied to the samples. These results suggest that the unipolar driven PZT thick films are applicable to MEMS devices.

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The crystal structure and strain in a (100)/(001)-oriented PZT micro cantilever under applied voltage were characterized by in-situ Raman spectroscopy. A Pt/LaNiO₃/(100)/(001)PZT/LaNiO₃/Pt/Ti/SiO₂/silicon-on-insulator (SOI) multilayer structure was fabricated in a process based on a microelectromechanical system (MEMS). The volume fraction of the domain switching from a-domains to c-domains was monotonously increased with increases in the applied voltage. No compressive in-plane lattice strain was induced in the PZT film with the increases in the applied voltage. These results show that Raman spectroscopy is a useful method for in-situ observation of PZT micro cantilevers.

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Amorphous Bi–Fe–O_x films prepared on SrTiO₃ (100) substrates using a conventional r.f. magnetron sputtering system were crystallized by post-annealing at 873 K in an atmosphere. Microstructural observations by X-ray diffraction and cross-sectional transmission electron microscopy revealed that the crystallized Bi–Fe–O_x films were well-epitaxially BiFeO₃ fabricated without interfacial layer although as-prepared film was amorphous structure with excess Bi. The crystallized BiFeO₃ films have fairly epitaxial compatibly ([001](001)BiFeO₃ // [001](001)SrTiO₃). These results indicate that (1) BiFeO₃ has good epitaxial compatibility with SrTiO₃ and (2) crystallizing amorphous Bi–Fe–O_x is one possible method that can be used to fabricate high-quality multiferroic barriers for tunnel junctions.

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Pr and Mn co-substituted BiFeO₃ (BFO) thin films were fabricated on a Pt-coated (100) SrTiO₃ substrates by pulsed laser deposition (PLD) method. X-ray diffraction patterns indicated that the formation of impurity phases was suppressed by Pr substitution in the BFO thin films. Furthermore, by combining with small amount of Mn substitution, Pr substitution was effective for reducing the leakage current density. The polarization vs electric field curves showed well-saturated hysteresis loops with measurement frequency of 20 kHz at room temperature. The remnant polarization at a maximum electric field of 1500 kV/cm was approximately 50–70 µC/cm².

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A measurement system with a high driving frequency of 100 kHz is effective for measuring the ferroelectricity of leaky ferroelectric materials such as multiferroic BiFeO₃ films. A high driving frequency reduces the measurement time, leading to a drastic reduction in the influence of the leakage current density on ferroelectric hysteresis loops. Phase-delay compensation is essential in a system with a driving frequency of 100 kHz; in this study a standard capacitor was used for phase-delay compensation. The value of remanent polarization of a BiFeO₃ film measured by the 100-kHz system was confirmed by a positive, up, negative and down measurement.

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Epitaxial xBi(Zn_1/2Ti_1/2)O₃–(1 − x)BiFeO₃ films were grown on (100)_cSrRuO₃//(100)SrTiO₃ substrates by metal organic chemical vapor deposition (MOCVD). The effects of x value on the crystal structure and the electrical properties were investigated. Constituent phase changed from rhombohedral symmetry to two types of tetragonal ones with different unit cell volume and tetragonality. Rhombohedral phase and the tetragonal phase with smaller tetragonality were not ascertained to transform to cubic phase up to 800°C from high temperature XRD results. Relative dielectric constant measured at room temperature showed the maximum value at x = 0.21 near the phase boundary between tetragonal and rhombohedral symmetries. Leakage current became small when the measurement temperature decreased at 80 K and the ferroelectricity monotonously decreased with increasing x values and was not ascertained above 0.26.

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We propose a calculation model that can predict the influence of interface on capacitance–voltage characteristics of metal-insulator-metal type thin film capacitor with perovskite type oxide. The simulation could successfully describe the results of capacitance–voltage measurements of the barium strontium titanate thin film capacitors with top electrodes of Pt, Au, and Ag. It is found that the electrode dependent on the tunability is derived from the work function of the electrode metal. The simulation model is base on the Schottky model that can be employed to explain the dielectric properties of metal/perovskite type oxide junction. The modified Schottky model considers the electric field dependence of permittivity and the back flow of electrons from metal to defect states located in the band gap of the perovskite oxide. This flow forms negatively charged space at the interface and affects the electric properties of the thin film capacitors.

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BaTiO₃ (BT) based perovskite films are expected as ferroelectric and piezoelectric materials alternating Pb(Zr,Ti)O₃ (PZT) films which involve toxicity of the lead. In the present study, we focus effects of bottom electrode structures on electrical properties of the BT films fabricated by Chemical Solution Deposition (CSD) method. The BT films were fabricated on 1–6 layered LaNiO₃ (LNO) bottom electrode on Si or Pt/Ti/SiO₂/Si substrate. The dielectric constant of the BT films fabricated on LNO/Pt/Ti/SiO₂/Si substrate showed higher values than that on the LNO/Si substrate. The dielectric constant and piezoelectric properties increased with increasing layer numbers of the LNO. The microstructure and crystal structure of the BT films was studied by means of X-ray diffraction, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM).

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This paper reports on two topics regarding nanosized barium titanate (BaTiO₃) prepared by the sol–gel method using a highly concentrated alkoxides precursor solution. One topic concerns the crystallographic features of the BaTiO₃ nanoparticles. In the case of using a highly concentrated precursor solution, non-core–shell BaTiO₃ nanocrystals with a small amount of intraparticle voids, lattice hydroxyl groups and remaining alkoxy groups were efficiently generated by the addition of less excess water during aging at room temperature. The generation of the high-quality BaTiO₃ nanocrystals is considered to be due to the hydrolysis and polycondensation reaction of the alkoxides being well promoted in such a concentrated solution. The lattice volume of the BaTiO₃ nanocrystals with a crystallite size of 15 nm fired at 600°C was approximately 1 vol % larger than that of bulk crystal. This lattice expansion is more likely to be caused by an intrinsic size effect than an extrinsic effect due to the lattice defects, such as lattice hydroxyl groups. The other topic concerns the dielectric properties of dense nanograin free-standing films with a grain size of 57 nm after applying the same sol–gel method. Significant frequency dispersion behavior of dissipation factor was observed at temperatures less than the Curie temperature. This finding may indicate that the dielectric properties reflect an intrinsic grain size effect without any influence being attributed to the film/substrate interface or lattice defects.

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Analysis of asymmetric Raman line shape disclosed the variation of phonon correlation length in A₁(3TO) mode, L_A1(3TO), with temperature in the ceramics of BaTiO₃ (BT), Ba_0.6Sr_0.4TiO₃ (BST-0.6) and BaZr_0.25Ti_0.75O₃ (BZT-0.25), namely normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics) and relaxor ferroelectrics, respectively. In BT, L_A1(3TO) exhibited steep increase at the Curie temperature (T_c) on cooling. This is attributed to the formation of the ferroelectric domains at the T_c. Both BST-0.6 and BZT-0.25 showed gradual increase in L_A1(3TO) on cooling across the dielectric maximum temperature (T_m), indicating the continuous increase in the average size of the polar nanoregions (PNRs). Normal ferroelectrics can be distinguished from DPT and relaxor ferroelectrics in this point. L_A1(3TO) of BZT-0.25 was longer than that of BST-0.6 near the T_m. This suggests the size of PNRs in BZT-0.25 is larger than that in BST-0.6. Huge dipole polarization of BZT-0.25, giving rise to the strong relaxor behavior, could be originated from the contribution of the large PNRs near the T_m. DPT ferroelectrics can be also differentiated from relaxor ferroelectrics in terms of the average size of PNRs.

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Barium titanate (BaTiO₃, BT)–bismuth magnesium titanium oxide (Bi(Mg_0.5Ti_0.5)O₃, BMT) solid solution system ceramics were prepared using nanoparticles in atmosphere to enhance Curie temperature (Tc) of BT, 132°C, to much higher temperature. Optimization of calcination and sintering conditions resulted in a formation of a perovskite single-phase, and their densities were always greater than 94%. The synchrotron XRD measurement revealed that the all ions in the ceramics had almost homogeneous distribution. Temperature dependence of dielectric property revealed that the BT–BMT system ceramics was typical relaxor materials, and for the 0.5BT–0.5BMT ceramics, the dielectric maximum was clearly observed at 360°C. Finally, their apparent piezoelectric constant (d^*) were measured by electric-field dependence of strain at room temperature, and the d^* value was measured at around 60 pm/V for the 0.4BT–0.6BMT ceramics.

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Barium titanate (BaTiO₃, BT) and strontium titanate (SrTiO₃, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST.

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Barium titanate (BaTiO₃, BT)–potassium niobate (KNbO₃, KN) solid solution system (0.5BT–0.5KN) ceramics with various microstructures were prepared by two-step sintering method, and their piezoelectric properties were investigated. For 0.5BT–0.5KN ceramics, two phases, ferroelectric tetragonal and ferroelectric orthorhombic, coexisted in different grains at room temperature, owing to the limited solid solution system. The volume fraction of interface region between BT-rich tetragonal and KN-rich orthorhombic grains was controlled by sintering temperatures, and increased with decreasing sintering temperatures. Apparent piezoelectric constant d₃₃^* was measured using slope of strain vs. electric field curves. As the results, the d₃₃^* increased with decreasing sintering temperatures, which revealed that interface region between tetragonal and orthorhombic grains could contribute to enhancement of piezoelectric properties.

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Platelet KNbO₃ particles having perovskite single phase have been successfully synthesized by a new simple procedure based on the dry-mixing technique and self-flux method using KNO₃ source that required no washing and filtration process. Well-crystalline edge-shaped platelet KNb₃O₈ particles were first obtained by the reaction between KNO₃ and Nb₂O₅. Next, they were reacted with second KNO₃ to form platelet KNbO₃ particles by the topochemical conversion method. The platelet KNbO₃ particles synthesized at 800°C demonstrated a relatively high aspect ratio of around 5 with edge lengths of about 2–10 and 10–40 µm in size for the tabular and thickness directions, respectively. The topochemical conversion mechanism from KNb₃O₈ to KNbO₃ was also proposed in this study.

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Rhombohedrally distorted perovskite BiFeO₃–K_0.5Na_0.5NbO₃ ceramics with ferroelectricity and ferromagnetism were synthesized by solid-state reaction. The effect of K_0.5Na_0.5NbO₃ content on the crystal structure, electrical and magnetic properties of a BiFeO₃–K_0.5Na_0.5NbO₃ system was examined with a view to achieving multiferroic BiFeO₃-based ceramics. Perovskite BiFeO₃–K_0.5Na_0.5NbO₃ single phase was obtained by formation of solid solution with K_0.5Na_0.5NbO₃, whereas pure BiFeO₃ ceramics contained a small amount of a second phase, such as Bi₃₆Fe₂O₅₇. The crystallographic symmetry of BiFeO₃–K_0.5Na_0.5NbO₃ changed from rhombohedral to cubic when the content of K_0.5Na_0.5NbO₃ exceeded 15 mol %. The rhombohedrally distorted BiFeO₃–K_0.5Na_0.5NbO₃ showed a high Curie temperature (>770°C) and weak ferromagnetism at room temperature. Dielectric properties of the resultant ceramics were improved by controlling the amount of Mn doping to facilitate ferroelectric measurements.

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We report the structure and electric properties of La₃Ta_0.5Ga_5.5−xAl_xO₁₄ (LTGAx, x = 0.0 (LTG), 0.3 and 0.5) single crystals, with a Ca₃Ga₂Ge₄O₁₄-type structure, suitable for high temperature piezoelectric application. A single-crystal X-ray structure analysis reveals that Al atoms are distributed in all cation sites except for the decahedral site occupied by La, which favors instead the octahedral site. The piezoelectric moduli d₁₁ kept a constant, whereas |d₁₄| increased 14% with the increasing Al content, x, up to 0.5. The LTGA0.5 crystals showed a low temperature dependence (2% deviation from room temperature to 400°C) of d₁₁ and a higher electric resistivity ρ than those of the LTG crystals. The Al substitution is effective for improving the electrical properties of the LTG.

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Single crystals of K_0.14Na_0.86NbO₃ (KNN) and Mn-substituted KNN (Mn-KNN, K_0.14Na_0.86Mn_0.005Nb_0.995O_y) were grown by a flux method, and the effects of Mn substitution on the leakage current, polarization and dielectric properties were investigated along [100]_cubic. As-grown and annealed (850°C in air) crystals did not show an apparent polarization hysteresis loop due to its large leakage current density (∼10⁻³ A/cm²). The annealing at 1100°C in air led to a marked decrease in leakage current density of the order of ∼10⁻⁶ A/cm² for KNN crystals. Mn-KNN crystals annealed at 1100°C in air exhibited a low leakage current density of ∼10⁻⁸ A/cm². Electron spin resonance measurements and defect chemistry analysis show that the average valence increase of Mn by oxidation treatment (the annealing in air) absorbs electron hole, the carrier of the leakage current, which is suggested to be the origin of the low leakage current observed for Mn-KNN crystals.

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This paper reports on the piezoelectric anomalies at the temperature or composition-induced ferroelastic phase transitions of tungsten bronze ferroelectrics. First, the temperature-dependent piezoelectric properties of Sr_1.9Ca_0.1NaNb₅O₁₅ (SCNN) ceramics were characterized using a resonance/anti-resonance method. SCNN has a ferroelastic phase transition manifested by a broad dielectric peak in the temperature range of −60°C to 20°C. The electromechanical coupling factor and elastic compliance showed the maximum at −40°C, increasing the transverse piezoelectric constant (d₃₁) by 38% compared with the room temperature value. Tungsten bronze ferroelectrics follow a trade-off relationship between the longitudinal piezoelectric constant (d₃₃) and the Curie temperature, while SCNN deviates significantly from the trend curve. This deviation is attributed to the ferroelastic phase transition close to room temperature.
Second, the ferroelastic phase transition was investigated for epitaxial films of (1 − x)(Sr₃Ba₂)Nb₁₀O₃₀–xBa₄Bi_2/3Nb₁₀O₃₀ as a function of the composition. A careful structural analysis by X-ray diffraction revealed that there is a ferroelastic phase boundary between tetragonal and orthorhombic crystals at x = 0.06–0.3. The electric field-induced strain and the relative dielectric constants characterized at 80 K for the epitaxial films increased in the vicinity of the phase boundary composition. These results suggest that engineering the ferroelastic phase transition is an approach to improving the piezoelectric properties of lead-free tungsten bronze ferroelectrics.

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Fabrication and property of c-axis-oriented KSr₂Nb₅O₁₅ (KSN) ceramics were examined. Particle-oriented KSN was fabricated by using a rotating magnetic field and subsequent sintering. KSN fine powder was prepared by conventional solid-state reaction and grinding processing. C-axis-oriented KSN green compact was fabricated in a rotating magnetic field 10 Tesla. The resulting green body was sintered at 1473 K for 6 h and then at 1525 K for 2 h to prevent exaggerated grain growth. C-axis-oriented KSN ceramics with relative density 92% was obtained. In XRD, peaks from the c-planes, such as 001 and 002, were very strong at the horizontal cross section of the sintered specimens. The ferroelectric and piezoelectric property along to c-axis was also improved to 21 µC/cm² and d₃₃ = 101 pC/N by orientation structure.

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Multilayer prototype actuators were demonstrated using (Bi_1/2Na_1/2)TiO₃ [BNT]-based ceramics as active layers and Pt as internal electrodes. One of the BNT-based solid solutions, 0.68(Bi_1/2Na_1/2)TiO₃–0.04(Bi_1/2Li_1/2)TiO₃–0.28(Bi_1/2K_1/2)TiO₃ (BNLKT4–28) has been selected as the an active layer and it showed a relatively large piezoelectric strain constant d₃₃ of 130 pC/N and a high depolarization temperature T_d of 226°C. The total number of layers was 10 and the active layer thickness was 125 µm for the sintered body. The final compact dimensions were approximately 5 × 5 × 2 mm³. From the SEM observation, there were no apparent delaminations around the interface between Pt electrodes and active BNLKT layers. The large electric-field-induced strain at 70 kV/cm was 0.17% and the longitudinal dynamic displacement at the same electric field was 2.1 µm.

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We propose use of a liquid phase deposition method (LPD) to prepare the composite ceramics with no chemical reaction between the two phases. Mg₂SiO₄–TiO₂ composite ceramics is desirable for microwave/millimeter-wave dielectric devices, because the appending TiO₂ into Mg₂SiO₄ improves the temperature coefficient of resonant frequency (τ_f) to 0 ppm/°C. However, there is a problem that the secondary phases: MgSiO₃ and MgTi₂O₅ are created during sintering at elevated temperatures. The presence of the secondary phase results in decrease of the quality factor (Q·f). To prevent the production of the secondary phase, we try to investigate another route to prepare the Mg₂SiO₄–TiO₂ composite ceramics using a liquid phase deposition (LPD) process as follows: Porous Mg₂SiO₄ ceramics were prepared by sintering Mg₂SiO₄ with pore-forming agents. Then, TiO₂ was deposited into the pores using LPD. In particular, this study focused on two conditions to deposit TiO₂ in porous Mg₂SiO₄: (1) the firing temperature after depositing TiO₂ in the porous Mg₂SiO₄ and (2) the concentration of the precursor solution for the LPD.

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Thin films of Ba(Zr_0.2Ti_0.8)O₃ (BZT) were prepared on Pt/Ti/SiO₂/Si and Pt/TiOx/SiO₂/Si substrates by chemical solution deposition. The alkoxide–hydroxide method was applied. The temperature dependence of the electrical and electromechanical properties of the BZT thin films was investigated. Application of a Pt/TiOx/SiO₂/Si substrate is effective in suppressing the unknown phase formation and in obtaining high permittivity of 1080 and tunability under 400 kV/cm of 84%. The XPS depth profile reveals that titanium and oxygen are richly present close to the BZT/Pt interface of the films on a Pt/TiOx/SiO₂/Si substrate. The temperature dependences of permittivity, tunability and field-induced strain are slight between −100°C and 100°C. The piezoelectric coefficient at room temperature estimated from the slope of the displacement loop is 35 pm/V.

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Tetragonal BaTiO₃ was prepared by reaction of a layered K₂Ti₂O₅ and mixed barium salts (BaCl₂ + Ba(NO₃)₂) at above 700°C. The morphology of the particle was cubic shape and the particle size of the products prepared at 700–1000°C was ∼10 µm, and that of the products prepared at higher temperatures (1100–1200°C) was smaller than that of the products prepared at 700–1000°C. From the chemical analysis no potassium atom was detected and the Ba/Ti ratio in the tetragonal BaTiO₃ was 1.00. In the cubic particle of the tetragonal BaTiO₃ surface 90° domain boundaries were observed. Lattice parameters and Curie temperature of the tetragonal BaTiO₃ were a = 3.995(1) and c = 4.036(1) Å and 130°C, respectively.

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Needle-like NaNbO₃ has been prepared in two steps by a molten NaOH method. First, Na₇(H₃O)Nb₆O₁₉·14H₂O precursor was synthesized by the reaction of Nb₂O₅ with a molten NaOH at 450°C for 50 h in air. The Na₇(H₃O)Nb₆O₁₉·14H₂O precursor was a needle-like single crystal 0.25–1.5 µm wide and >3 µm long. Then, the Na₇(H₃O)Nb₆O₁₉·14H₂O precursor crystal transformed to NaNbO₃ through an intermediate Na₇(H₃O)Nb₆O₁₉ by a heating above 500°C. The NaNbO₃ was a needle-like polycrystal with a perovskite-type structure.

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We have successfully fabricated non-firing porous ceramics from Black paper sludge ash (BPSA, waste materials). It is an alternative ecological and economic waste recovery technique for waste pulp materials from pulp and paper industries. It has been gradually affecting our environment. In this study, black paper sludge ash (solid waste, BPSA obtained from a waste material from pulp and paper industries) was investigated for the fabrication of porous ceramics. The BPSA was activated with mechano-chemical process. Then, KOH solution was added and reacted to the paste (waste composite) until completely solidified. The structural properties of the porous ceramics were investigated using X-ray CT and mercury porosimeter. Results show increasing the concentration of KOH solution and reaction temperature created an observable pore size of specimen and a number of noticeable pores in the specimen increased.

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Hydroxyapatite (HA: Ca₁₀(PO₄)₆(OH)₂) ceramic coating on magnesium (Mg) alloy (AZ31; Mg–3Al–1Zn) was achieved simultaneously by using a double layered capsule hydrothermal hot-pressing (DC-HHP) method at the low temperature as low as 150°C with no special surface treatment on the surface of the Mg alloy. A mixture of calcium hydrogen phosphate dehydrate (DCPD) and calcium hydroxide (Ca(OH)₂) was used as a starting powder material for solidifying HA. Pull-out tests were conducted in order to obtain an estimate of adhesive properties for the HA coating to the Mg alloy. Average value of maximum shear stress was determined to 6.1 ± 1.0 MPa. After the pull-out fracture tests, it was revealed that HA ceramics remained on the surface of the Mg alloy. The Mg alloy could be bonded to HA ceramics with good adhesive properties.

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Recently, regeneration therapy has been developed and uses a cellular activity to cure bone defects, requiring HAp with porous spaces for the cells. We have developed superporous HAp (HAp-S). The macro pore size of HAp-S was approximately 50 to 300 µm. The macro pores were very uniform. Moreover, HAp-S had many interconnecting pores and micro pores on the pore wall. HAp-S showed regenerative bone tissue, integration with the surrounding tissue and recovery of the compression strength of the defect area in the early stage. These results strongly suggest that the controlled triple pore structure, namely, uniform macro pores, many interconnecting pores and micro pores on the pore wall, advances osteogenesis. HAp-S was confirmed to have the most suitable pore structure for bone regeneration as the bone substitute material, and as being a useful material for application to bone disease.

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The synthesis and emission spectrum control of novel Eu²⁺-activated amorphous alkaline earth silicate phosphors from the reduction of Eu³⁺-activated amorphous alkaline earth silicate phosphors is reported. The as-prepared Eu³⁺-activated amorphous alkaline earth silicate phosphors emitted red. Reduction using Ni-metal powder in a H₂ (5%)/Ar (95%) atmosphere produced Eu²⁺-activated amorphous barium silicate phosphor that emitted green. Eu²⁺-activated amorphous calcium silicate was produced by reduction with ammonium chloride in air and emitted purple-blue. It was possible to control the emission spectrum by changing the reduction time. These results suggest the possibility to use three-band type phosphors for the fabrication of white light emitting diodes using one host crystal.

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Hydroxyapatite (HA) particles synthesized by hydrothermal treatment of octacalcium phosphate (OCP) particles were characterized in detail and the reaction mechanism was discussed. The calcium-deficient HA particles were firstly formed and their compositions gradually closed to the stoichiometric composition with reaction progress. While their compositions closed to the stoichiometric composition, split of plate-shaped HA particles into smaller strips and subsequent crystal growth of HA particles were observed. The [001] direction of synthesized HA was parallel to the [001] direction of starting material of OCP. The hydrothermal treatment of OCP particles is useful for synthesis of plate-shaped HA particles with different morphologies and compositions.

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Recently, zirconia films have attracted considerable attention because of their potential applications in solid oxide fuel cells and as thermal barrier coatings and oxygen sensors. Herein, we report that high-density zirconia films can be formed at room temperature by using the aerosol gas deposition (AGD) technique and discuss the conditions required for film formation. The experimental results indicate that the particle size and specific surface area of the zirconia powder used determine the success of film fabrication by AGD. Films are successfully formed when the mean particle size and specific surface area of the powder are in the range 2.1–3.5 µm and 4.4–6.5 m²/g, respectively.

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Geopolymer–zeolite hybrid bulk materials were formed in-situ from as-received coal fly ash powder by a simple two-step treatment: (1) immersing the coal fly ash powder packed within a cylindrical acrylic pipe into a 3.5 mol/l Na(OH) solution at 80°C and (2) subsequent curing in a temperature–humidity-controlled chamber at a fixed condition: 50°C and 50% relative humidity. The content of the formed Na-X type (conversion ratio from the starting coal fly ash) in the sample was optimized to be approximately 10% when the duration of the immersion in Na(OH) solution reached 72 hours. The compressive strength at room temperature of the in-situ formed bulk samples exhibited a clear tendency to increase with both alkali immersion time and curing time, which could be due to the increase of the amount of the in-situ formed geopolymer. As a result, after the 96-hour-alkaline immersion followed by the 21 days curing, the average compressive strength at room temperature achieved 5.4 MPa. This value was found to be more than four times higher than that of the samples without curing treatment (1.3 MPa).

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