Hajime Haneda

Evaluation of oxide ion diffusivity in YAG ceramics

Abstract Transparent yttrium aluminium garnet (YAG) polycrystal can be used as a host material for a solid state laser. In the present study, the authors prepared completely transparent YAG ceramics from active powder. The optical and mechanical properties of YAG ceramics are very sensitive to point defects. In order to examine the relationship between these properties and point defects, it is first necessary to characterise the defects. The authors report the effect of doping on oxygen diffusivity in several YAG ceramics, doped with various elements. Although Nd doping slightly increases the oxygen diffusion coefficient and the number of oxygen vacancies increases with increasing Nd concentration in as sintered materials, the variation of the oxygen diffusion coefficient in well annealed samples is small. These results suggest that the oxygen vacancies exist in non-equilibrium. However, grain boundary diffusivity was not influenced by preannealing before the oxygen diffusion experiments. The oxygen defect structure in transparent YAG ceramics is also discussed.

Compositional characterization of nano-materials and thin films with secondary ion massspectrometry

Characterizations of nanomaterials and nano-process are essential studies in order to establish fabrication processes of the nanomaterials and to optimize their conditions. The structural and compositional characterization is considered to be a first step for this kind of study. Secondary ion massspectrometry (SIMS) is one of the useful methods to analyze the composition, particularly trace elements. Advantages and disadvantages of SIMS analytical technique are discussed, comparing with other methods. Nano-particles patterning process is explained, using zinc oxide nano-particles. Its evaluation is carried out by means of a static SIMS, as example. Finally, the recent development of the novel Nano-SIMS is briefly mentioned, and then its application is reported, concerning with the grain boundary analysis of ceramics consisted with fine grains.

Elongated lattice relaxation on a ZnO(0001) surface

A ZnO single crystal has the (0001) polar surface terminated by Zn ions. The lattice relaxation of the surface was investigated on the basis of DV-X/spl alpha/ calculations. The covalent bond strength took a maximal value for the lattice elongation of 0.04 nm, being ascribed to the decrease in antibonding. The covalent bonding plays an important role in the lattice relaxation of the (0001) ZnO surface.

Oxygen diffusion and defect structure in PTCR-barium titanate

The diffusivities of oxygen along the grain boundary in the PTCR-samples were greater than those in non-PTCR samples. The grain boundary diffusion characteristics drastically changed at the oxygen partial pressure of appearing the PTCR effect. On the other hand, the volume diffusivities of oxygen ions in both samples have the same value. These results lead that the structural change at grain boundary in polycrystalline barium titanate occurred at the oxidizing prossece and enhanced oxygen grain boundary diffusion. The origin of the barrier layer of the PTCR effect is considered to be same.