Key Engineering Materials Vols. 421-422

Abstract: Thin films of Si-added-MoSi2 were deposited on Si3N4 or alumina substrate using an RF magnetron sputtering with a target made of MoSi2 and Si powders. The thin film consisted of a mixture of Si and MoSi2. The resistance of MoSi2-thin-film heaters fabricated using Si3N4 substrate heated for a long time in air increased with increasing heating-time at temperatures near 420°C due to generation of MoO3, which is an insulator, in thin film due to the oxidation of Mo in MoSi2. On the other hand, oxidation-resistant capability of thin-film heater fabricated by adding Si to MoSi2 was drastically improved compared with MoSi2 thin-film heater, because Si particles or the Si layer on a MoSi2 particle prevented the oxidation of MoSi2. The oxidation-resistant capability was excellent in air at high temperatures near 480°C for a long heating-time exceeding 950h.

Abstract: TiO2-nanoparticles of anatase-type were synthesized and deposited using the electrophoresis depo-sition method. All of TiO2-nanoparticles were positively charged in colloidal aqueous solution and were attracted toward ITO glass as the negative electrode as same as nanoparticles (P25) whose diameter is larger than that of TiO2-nanoparticles. Many of the TiO2-nanoparticles were connected with each other and formed clusters, although single TiO2-nanoparticles were also observed. The cracks generated in the thin film with increasing the deposition time and thin film was flaked off from substrate. High optical transparency TiO2-nanoparticles-thin film without cracks was deposited when the deposition time was short. Moreover, the thickness of TiO2-thin film, which has high optical transparency and no cracks, could be increased using mixture of TiO2-nanoparticles and P25.

Abstract: In this work, the ferroelectric hysteresis in thin films was investigated with Monte Carlo simulation using the DIFFOUR Hamiltonian and the Metropolis algorithm. The field frequency, the filed amplitude and the thickness dependence of hysteresis properties were found. For instance, at high enough field, the area increases, maintains and reduces with increasing frequency. However, with increasing the film’s thickness, the area increases over the whole considered frequencies, and the frequency at maximum area shifts to a lower frequency due to the stronger ferroelectric coupling in thicker films. This strongly indicates the thickness dependence of the ferroelectric hysteresis. In addition, the power law scaling relation between the hysteresis properties and input parameters, which are the film’s thickness and the field parameters, were proposed. The scaling exponents were compared and discussed with previous investigations on thin ferroelectric films.

Abstract: Li(Ga1-xMx)O2 (M: B or Al) single crystals are grown by Floating zone method. These crystals are characterized from the viewpoint of the substitution of M, such as lattice parameter (lattice volume) change, piezoelectric properties and nonlinear optics. The lattice volume is decreased with the increase of Al content for Al-substitution largely, but the change is a little for B-substitution.

Abstract: The ferroelectric glass-ceramic of the composition Na2O-Nb2O5-Al2O3-SiO2 was prepared by controlling crystallization of the glass that added with small amount of TiO2. The effect of TiO2 content on crystallization behavior and the dielectric property were determined. X-ray diffraction studied indicated that NaNbO3, NaNbO8 and a compound of alkali alumino silicate composition were readily formed in the as-quenched glass as the product of phase separation. After treatment at 700oC for various times, NaNbO3 volume fraction was found to increase with time. Crystalline size of the NaNbO3 was lower than 300 nm and it was developed with treatment time. Presence of TiO2 had considerably effect on NaNbO3 volume fraction when treatment time shorter than 1.0 h. The dielectric response of the glass-ceramic samples was found to arise from all contributions of crystalline phases and glass matrix responds.

Abstract: Zinc isotopic heterostructured zinc oxide thin films of 64ZnO/68ZnO/64ZnO were synthesized using pulsed laser deposition. The pulsed laser was first irradiated onto a polycrystalline target of 64ZnO to deposit the 64ZnO layer, then onto the 68ZnO target to prepare the 68ZnO layer and finally, the 64ZnO target was used again. The 64ZnO/68ZnO/64ZnO layered thin film was thus obtained. The thin films were annealed at various diffusion annealing temperatures. Diffusion profiles of the zinc isotopes due to the annealing were evaluated using secondary ion mass spectrometry (SIMS). The diffusion coefficients were slightly higher near the interface between the thin film and the substrate (the inner region) compared to the near surface (the outer region).

Abstract: Diffusion behaviors of aluminum (Al) in zinc-oxide (ZnO) single crystals were measured by means of ion implantation technique and SIMS depth profiling. It was found that Al concentration profile had a peculiar shape with a constant-concentration region and a steep tail, which was also found in profiles of other donors such as Ga and In. Detailed analysis of the profiles revealed that the diffusivity of Al was proportional to the square of Al concentration and its intrinsic diffusivity was much smaller than previously reported values. Oxygen diffusion experiments were also performed and the implantation of Al ions enhanced the oxygen diffusion coefficients by about 20 times. This result indicates that oxygen interstitial diffusion occurs in n-type ZnO.

Abstract: The relationship between the defect structure and luminescence property of ZnO ceramics implanted with Ar of 2×1015 – 60×1015 ions/cm2 was studied. After annealing, the heavy dose-implanted sample (Ar ≥ 30×1015 ions/cm2) was characterized by a luminescence peak at the 730-nm wavelength. Defects in the implanted region formed voids during post-annealing. Oxygen tracer experiments indicated that grain boundary diffusion in the implanted region was enhanced significantly.

Abstract: The gas pressure and the types of ambient gas dependence of X-ray intensity were investigated for LiNbO3 single crystals polarized in the c-axis direction at pressures of approximately 1 to 30 Pa. The integrated X-ray intensity showed a local maximum value at the pressure Pmax. Pmax moved to the high-pressure side in the ambient with a large first ionization energy. Pmax was proportional to the Boltzmann factor using the first ionization energy of each ambient gas molecule. The X-ray intensity was approximated using the quadratic function, which was convex upward for the pressure. It was found that one of the causes of the decrease in X-ray intensity on the pressure side higher than Pmax was the adsorption of positive ions on the crystal electric surface.

Abstract: ZnO varistors of the excellent tolerance characteristics for electrical degradation were made by adding Bi2O3-MnO2-Co3O4-Cr2O3-SiO2-Sb2O3-NiO in ZnO. The tolerance characteristics for electrical degradation were evaluated by changing amount of ZrO2-additive. The evaluation methods are voltage-current characteristics, X-ray diffraction, scanning electron microscope, and energy dispersion X-ray spectroscopy. Monoclinic and tetragonal ZrO2 and the compounds originated in Zr were observed at both grain boundaries and triple points. Moreover, the compounds originated in both Zr and Sb improved the tolerance characteristics for electrical degradation. On the other hand, especially monoclinic ZrO2 deteriorated the tolerance characteristics for electrical degradation. It is one key factor of the improvements of the tolerance characteristics for electrical degradation that the mobility of oxide ions or interstitial Zn2+ ions was hindered by forming the compounds contained Zr, Sb, Si, and, Bi atoms.