Key Engineering Materials Vol. 485

Abstract: The resistivity of transparent conductive thin film formed by sputtering exhibits a dependence on film thickness. In this study, an analysis by electromagnetic field simulation of resistance effect on the transmission characteristics was carried out. The overall resistance of the signal waveguide governs the transmission characteristics, and variation of the resistance at the interface between the substrate and the thin film has no significant effect. We evaluated a structure in which fine metal wiring that is not visible to the eye is placed on transparent conductors to reduce the resistance of the transmitting waveguide. Electromagnetic field simulations suggest that this structure improves the transmission characteristics while keeping high transparency.

Abstract: Equipment was designed for the application of Al₂O₃ thin films by the aerosol deposition method (ADM) at room temperature. Al₂O₃ film could be deposited on Pyrex-glass, indium tin oxide (ITO), polyvinyl chloride (PVC) plastic, single crystal silicon, and sapphire substrates. The films had the same crystal structure as the raw material particles and were highly transparent. The breakdown electric field of the Al₂O₃ film for the ADM was more than 35 kV/mm.

Abstract: The processes for polishing a ZnO surface were investigated with the aim of establishing a process for obtaining an atomically flat surface with high crystalline quality. The defects in a layer undergoing mechanical polishing were monitored through photoluminescence measurements, and the purity of the polished surface was characterized by SIMS. An atomicallyfishing process.

Abstract: This study examined effects of applying a magnetic field (up to 2 kG) on the magnetic properties of epitaxial NiFe₂O₄ (NF) thin films during deposition. The NF films were deposited on Y_0.15Zr_0.85O1.93 (YSZ) buffered Si (001) substrates using pulsed laser deposition (PLD). Although application of magnetic field during deposition affected neither the crystal structure nor orientation of the NF thin films, it improved magnetic properties. The saturation magnetization (Ms) of NF thin films deposited at 500°C and 600°C without application of a magnetic field was as low as 40 emu/g. However, that of NF deposited under magnetic field of 2 kG got to bulk Ms (50.3 emu/g). The TEM observation results revealed that the anti-phase boundary (APB) density decreased by application of the magnetic field during deposition. Results show that magnetic properties of NF thin films are controllable using the magnetic field during deposition.

Abstract: The effect of Al₂O₃ addition on the temperature dependence of the initial permeability and microstructure of NiCuZn ferrites is investigated. The temperature dependence of initial permeability decreases with an increase in Al₂O₃ addition. EPMA analysis reveals that Al₂O₃ dissolves in the NiCuZn ferrite grains but is not uniformly dispersed. Separation of the initial permeability into two components, one due to spin rotation and the other due to domain wall motion, reveals that with an increase in the Al₂O₃ addition, the temperature dependence of the domain wall motion component decreases, while that of the spin rotation component shows no notable change. This indicates that the decrease in the temperature dependence of initial permeability may be attributed to the influence of Al₂O₃ on the domain wall motion.

Abstract: In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μ_r^*, the relative complex permittivity ε_r^*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO₂. When ferrite particles were dispersed and isolated in an SiO₂ medium, the frequency dependence of μ_r^* was different from that for a composite made of SiO₂ particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO₂ was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO₂ particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO₂ medium.

Abstract: The magnetic properties of an artificial multiferroic material, a Cr₂O₃/LiNbO₃/Cr₂O₃ hetero structure with various-thickness LiNbO₃ layers, were investigated. All samples showed ferromagnetism due to the existence of oxygen deficiency or an excess of the Cr₂O₃ layer in the LNO/Cr₂O₃ interface. The ferromagnetism of the samples was affected by the crystal orientation of the LiNbO₃ layer, and seemed to have a major impact on the magneto-electric behavior of this hetero system.

Abstract: We investigated the electrical properties of the perovskite R(Cr,Mn)O₃ (where R is selected from various rare earth elements and Y), which is suitable for use in negative temperature coefficient (NTC) thermistors. The substitutions of Mn for Cr in La(Cr,Mn)O₃ and larger ions for R³⁺ decreased both the resistivities (r) and thermistor constants (B values) estimated from measurements at 25°C and 50°C according to r = r₀exp(B/T). The activation energies of the carrier number (E_g) and carrier mobility (W_H) were estimated by measuring the thermoelectric power and resistivity. A change in W_H corresponded to a change in the B value. We discussed the relationship between the grand state electronic configuration of the M³⁺ ions and the local lattice distortion around the M³⁺ ions. The change in W_H could be qualitatively linked to the M3d– O2p transfer energy, which is corresponding to the hybridization between the M3d and O2p orbital (M: transition metal elements, O: oxygen).

Abstract: BaTiO₃–(Bi_1/2K_1/2)TiO₃ (abbreviated as BT-BKT) solid solution ceramics, as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C, has been synthesized by sintering in N₂ atmosphere and after annealing in air over 1200°C. In the BT-BKT ceramics with PTC property, the impedance/modulus spectroscopic plots have revealed that a third resistance-capacitance (RC) response besides grains and grain boundaries. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers in the BT-BKT semiconducting ceramics.

Abstract: BaTiO₃–(Bi_1/2Na1/2)TiO₃ (abbreviated as BT-BNT) solid solution ceramics, as a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor material usable over 130°C, were synthesized in air atmosphere. By conventional processes, La-doping was not effective in giving semiconducting property to the BT-BNT ceramics because of volatilization of sodium and bismuth during sintering. By preventing the volatilization by lowering the sintering temperature using very fine TiO₂ powder and by adding calcium oxide to calcined BT-BNT powders, we obtained BT-BNT semiconducting ceramics which shows a resistivity change near Curie temperature.