Key Engineering Materials Vol. 566

Abstract: ron fluoride (III) anhydrate fine particle was prepared by drying in vacuum from FeF₃·3H₂O, a mechanical milling process and a calcination at 473 773 K. Particle size of FeF₃·3H₂O was ca. 3 5 μm and that of FeF₃ anhydrate was 100 500 nm after drying and milling. FeF₃ sample only after drying and milling was hygroscopic and became FeF₃·3H₂O under atmosphere. FeF₃ became stable under atmosphere after oxidation at 673 K for more than 20 minutes. It was found that Fe₂O₃ was produced by calcination and covered the surface of FeF₃ particles. In Charge-discharge measurements, the discharge capacity of these FeF₃ samples was 150 - 200 mAh/g at a discharge rate of 0.1 C. The oxidation could improve the discharge properties of FeF₃ cathode.

Abstract: Ce_0.8Sm_0.2O_1.9 (Samaria-doped ceria: SDC) precursors were synthesized by carbon-assisted spray pyrolysis. SDC thin films were prepared by electrophoretic deposition using the SDC precursor particles. The as-prepared SDC thin films were sintered at 1600 °C for 10 h. Uniform films with a thickness of approximately 20 μm were obtained. A fuel cell using the prepared thin films showed a maximum power density of 60.6 mW/cm² and an open circuit voltage (OCV) of 0.63 V at 700 °C.

Abstract: All contributions to the total conductivity, electrolyteelectrode interfaces, grain boundaries, ion-hopping, and optical phonons, were determined on the 8 mol% yttria-stabilized zirconia (8YSZ) and 8 mol% ytterbia-stabilized zirconia (8YbSZ) ceramics using the wideband conductivity spectroscopy. Complex conductivity spectra from 10¹ Hz to 10¹⁴ Hz were successfully obtained. The higher total conductivity of the 8YbSZ ceramics compared to the 8YSZ in wideband frequencies was mainly attributed to difference in the DC conductivity due to universal dielectric response (UDR), σ_dc; σ_{dc (8YbSZ)} > σ_{dc (8YSZ)}. Other parameters in the UDR and the optical phonon parameters did not greatly influence on the difference in their intrinsic conductivities.

Abstract: The electrochemical capacitors (ECs) have attracted a great attention as a rechargeable strage device with a high power density and high safety. An increase in specific capacity is demanded to use ECs in various applications. MnO₂ are expected as electrodes of ECs because of their large oxidation state change (Mn⁴⁺ Mn²⁺), low cost and environmental compatibility. When all manganese ions in the MnO₂ are completely reduced to Mn²⁺ from Mn⁴⁺ over a potential window of 1.1 V, the theoretical capacity is estimated to about 2000 Fg^-1. However, the reported capacity of MnO₂ electrodes are 100250 Fg^-1 [1-2] for powders and around 700 Fg^-1 [3] for thin films. Tunnel structured MnO₂ are expected to show high capacities by utilizing high ionic mobility in the tunnel and high surface area of tunnel walls. Fig. 1 shows crystal structures of (a) Pyrolusite (Tunnel size: 1×1), (b) Hollandite (Tunnel size: 2×2) and (c) OMS-5 (Tunnel size: 2×4) and (d) MnO₆ unit. In the present study, the relationship between the tunnel size and the specific capacity was investigated for those tunnel structured MnO₂. In addition, Hollandite /carbon composites were synthesized to improve the electrode properties of Hollandite.

Abstract: We evaluated the surface area, pore size distribution, and electrical characteristics of titanium oxide films formed under different sintering and cleaning conditions. In addition, we examined the microstructure of the titanium oxide films by forming cross-sectional surfaces. The necking structure of the titanium oxide films strongly influenced the conversion efficiency of the dye-sensitized solar cell. And, the conversion efficiency was improved by the increasing firing temperature and treating with TiCl₄ and ozone water.

Abstract: The effects of processing conditions on the morphologies of Mn-doped BiFeO₃ thin films have been investigated. BiFeO₃ thin films were prepared on a SrTiO₃ (001) substrate by CSD method. BiFeO₃ grew epitaxially on SrTiO₃ and Bi₂Fe₄O₉ has also orientation relationships with BiFeO₃. It was found that the formation of Bi₂Fe₄O₉ was promoted in an O₂ atmosphere. Island morphologies were observed in the BiFeO₃ thin films after post-annealing at 1023K both in N₂ and O₂ atmospheres. The formation of the islands is promoted in an O₂ atmosphere.

Abstract: Ferroelectric 0.7BiFeO₃-0.3BaTiO₃ and 0.7BiFe_0.95Mn_0.05O₃-0.3BaTiO₃ thin films were prepared by the chemical solution deposition. Perovskite single-phase thin films with homogeneous surface morphology were successfully fabricated at 700°C on Pt/TiO_x/SiO₂/Si substrates. Although typical polarization (P)-electric field (E) hysteresis loops were observed for 0.7BiFeO₃-0.3BaTiO₃ thin films, their insulation resistance was relatively low at room temperature. Mn doping for Fe site of the 0.7BiFeO₃-0.3BaTiO₃ was very effective in improving leakage current properties. In 0.7BiFe_0.95Mn_0.05O₃-0.3BaTiO₃ thin films, the abrupt increase in leakage current was suppressed even at high electric fields, leading to the well-shaped P-E hysteresis loops at ambient temperatures. Remanent polarization and coercive field of the 0.7Bi (Fe_0.95Mn_0.05)O₃-0.3Bi_0.5Na_0.5TiO₃ films at room temperature were approximately 26 μC/cm² and 130 kV/cm, respectively.

Abstract: Bi-based perovskite-type oxide materials such as BiFeO₃ (BFO) and Bi (Zn_1/2Ti_1/2)O₃ and the related compounds receive much attention and have been developed actively as important candidates for Pb-free ferroelectric materials instead of toxic Pb-based perovskite oxide materials. Recently, many researches have been reported for thin films of Bi-based materials by various film-deposition techniques for actual application of semiconductive devices, microactuators, etc. In this study, we tried preferential crystal growth of BFZT films on semiconductive silicon substrates using uniaxial-(100)-oriented LaNiO₃ (LNO) buffer layer. BFO films were fabricated via chemical solution deposition (CSD) technique on platinized silicon wafer [(111)Pt/TiO₂/(100)S and (100)LNO-coated platinized silicon [(100)LNO/(111)Pt/TiO₂/(100)S substrates. XRD analysis indicated that the films fabricated on (111)Pt/TiO₂/(100)Si substrate consisted of randomly-oriented BFZT crystal with lower crystallinity. On the other hand, the films on (100)LNO/(111)Pt/TiO₂/(100)Si consisted of uniaxial-one-oriented BFZT crystal with higher crystallinity. The crystallization temperature these films were 500°C, respectively. These results suggest that the BFZT crystal was grown successfully on uniaxial oriented (100)LNO plane which also had perovskite-type crystal structure. Consequently, one-oriented BFZT films were prepared on Si substrate successfully using (100)LNO buffer layer.

Abstract: We have elucidated the elastic interaction between the 90° domains and misfit dislocations in PbTiO₃/SrTiO₃ (001) epitaxial thin films by the local strain mapping based on high-resolution transmission electron microscopy. The novel mechanism of the nucleation and growth of 90 ̊ domain has been proposed based on the results, including the introduction of the additional dislocation perpendicular to the misfit dislocation and the dissociation of these dislocations into two pairs of partial dislocations with an anti-phase boundary.

Abstract: The microstructure of an epitaxial PbTiO₃ thick film was investigated by using transmission electron microscopy (TEM). An analysis of bright-field TEM (BFTEM) images revealed the existence of displacements along the [00 direction of PbTiO₃. High-resolution TEM (HRTEM) observation indicated that stacking faults parallel to the (001) plane of PbTiO₃ are formed in the thick film. Local strain fields around the stacking faults were quantified by geometric phase analysis of the HRTEM image. The measured strain suggested the presence of a pair of extrinsic and intrinsic stacking faults. The distance between an extrinsic stacking fault and an intrinsic one corresponds to two unit cells along the [00 direction of PbTiO₃. The formation of these stacking faults is considered to be associated with the strain relaxation of the film.