Papers by Author: Shunichi Hishita

Abstract: The effect of the surface preparation in samarium doped semiconducting barium titanate [(Ba_1-xSm_x)TiO₃] ceramics with (Ba, Sm)/Ti ratio of 1.000 was studied by means of isotope tracer technique using a secondary ion mass spectrometer. The surfaces of specimens were prepared with the chemical mechanical polishing (CMP) with colloidal silica slurry or the mechanical polishing (MP) with diamond paste. The oxygen diffusion coefficients obtained in the CMP samples were small compared to those in the mechanical polished samples. This fact suggests that the surface prepared with CMP has less oxygen defect concentration. Moreover, it was also indicated that high temperature treatment over 1000 °C is required for annihilation of defects formed by MP. The oxygen diffusion study used CMP sample brings the useful information on the oxygen defect chemistry in Sm doped BaTiO₃.

Abstract: The a-axis oriented ZnO thin films deposited on sapphire substrates by pulsed laser deposition were studied to investigate the effects of pre-annealing on oxygen diffusion. The effect was as follows: the oxygen diffusion coefficient decreased, and the oxygen concentration in the tailing regions of the profiles reduced. Ion images of an oxygen tracer revealed the high-diffusivity paths for oxygen tracer diffusion. The temperature dependence of oxygen tracer diffusion coefficients (D_b) in as-deposited and pre-annealed thin films were determined to be D_b [cm²/ = 9.2x10² exp (- 405 [kJ/mo / RT) and D_b [cm²/ = 1.8x10³ exp (- 418 [kJ/mo / RT), respectively. On basis of these results, the crystal orientation on D_b and the mechanism for oxygen diffusion were discussed.

Abstract: The relationship between Al and Li during diffusion was studied using Al-implanted ZnO. The Al donor in ZnO acts to increase the concentration of Li contamination from the atmosphere during the annealing. It is difficult to decompose the relationship formed by diffusion between Al and Li during high-temperature annealing. The most effective method to decompose the relationship is to anneal the as-implanted ZnO at a pressure of 5×10-3 torr. This annealing increases the Al solubility limit because the ZnO surface evaporates.

Abstract: The effect of ion implantation leading to contamination and diffusion of lithium impurity in ZnO ceramics substrates was investigated. The diffusion coefficients of Li in the implanted ZnO annealed at 1000 and 850°C were in good agreement with those in the non-implanted ZnO. At 700°C, Li diffusion in the implanted ZnO was strongly enhanced. Our results show that the defects introduced by the implantation enhance the impurity diffusion at low temperature annealing.

Abstract: The defect structure of undoped ZnO and (Zn1-x,Mgx)O solid-solution films were deposited on YSZ substrate with pulsed laser deposition (PLD) to investigate defect equilibria in those films. In particular, the effects of thermal treatment on the structures and prosperities of (Zn1-x,Mgx)O
solid-solution films were examined. The films with high MgO concentration (x>0.12) decomposed to the wurtzite-type and rock-salt-type phase after thermal treatment, indicating that the solubility limit of Mg was about x=0.12 and the wurtzite-type (Zn,Mg)O films with x>0.12 were indicated to be non-equilibrium ones. The subsequent analyses of oxygen diffusivity in those films revealed that the films under non-equilibrium state, i.e., wurtzite-type (Zn1-x,Mgx)O with x>0.12, contained significantly high concentration of anion defects.