Papers by Author: Minoru Osada

Abstract: We prepared a niobiophosphate-glass-crystallizing tungstenbronze-type Ba₂NaNb₅O₁₅ and measured elastic light scattering spectra in situ in the glass-ceramics fabrication regime. We found that the studied glass possesses a strong tendency for phase separation into Al₂O₃P₂O₅ and Nb-rich regions prior to crystallization. It is suggested that the tungstenbronze phase crystallizes in the Nb-rich region separated from the supercooled liquid phase. This study demonstrated that in situ Raman spectroscopy is also useful for observing the phase separation dynamics in glass.

Abstract: We investigated the crystallization and resulting morphology of a stoichiometric barium-silicate glass 1BaO-2SiO₂ (glassy sanbornite) by using transmission electron microscope and Raman spectroscopy. A crystalline aggregate structure consisting of a Ba₅Si₈O₂₁ phase (trunk) and a β-BaSi₂O₅ phase (branch) was observed in the heat-treated glassy sanbornite. The Ba-richer phase of Ba₅Si₈O₂₁ precipitated prior to the formation of the stoichiometric β-BaSi₂O₅ phase, suggesting the presence of the region in which the Ba ions are enriched or cohesively distributed. A considerable structural similarity between the glassy sanbornite and the Ba₅Si₈O₂₁ phase was also suggested in this study.

Abstract: (100)/(001)-oriented PZT thick films were grown on SrRuO3//(100) SrTiO3 and (100) MgO substrates by matel organic chemical vapor deposition (MOCVD) with different volume fraction of (001) orientation, and were compared with (001) single-oriented epitaxial PZT thick films grown on SrRuO3//LaNiO3//(100) CaF2 by polarized Raman spectroscopy. The spectra from (100)-oriented domain and (001)-oriented domain can be individually observed for the films with the mixture orientation of (100)/(001). Raman analysis revealed the different strain state of (100)-oriented and (001)-oriented domains. Moreover, the rotation dependence of A1(1TO) mode could be explained by the calculation using the volume fraction of (001)-oriented domains obtained from X-ray reciprocal space mapping analysis for the films with the mixture orientation of (100)/(001). These results suggest the local structure characterized by Raman spectroscopy almost agreed with the structure characterized by XRD analysis for the films with the mixture orientation of (100)/(001).

Abstract: We report a fabrication of high-density nanodots by photodoping in overdoped Bi2Sr2CaCu2O8+d thin film (Tc = 80 K). A scanning near-field optical microscope probe is used to locally excite carrier, and photodoped region is associated with lower Tc phase (Tc = 75 K) via overdoping. Nanoscale characterizations with optical reflectivity reveal that nanodots (30-nm diameter) are regularly distributed in 50-nm step. The resultant films with photoinduced nanodots enhance Jc, a situation being similar to strong pinning effects observed in films modified by either ion irradiation or sputtered nanoparticles. These results suggest that photoinduced nanodots with lower Tc act as effective pinning centers.

Abstract: High-resolution photoluminescence (PL) measurement was carried out for copper aluminum disulfide (CuAlS2) powder at 12 K. Several sharp PL lines were observed in the range from 3.580 to 3.320 eV. The emission peaks at photon energies from 3.566 to 3.459 eV were attributed to free-exciton (FE) and bound-excitons (BE). The several weak emissions at below 3.476 eV were clarified to be phonon replicas (PR) by Raman scattering and in the viewpoint of exciton-phonon interaction. We observed the one, two and three-phonon replicas related to E(LO, TO) and B2(LO, TO) vibrational modes in chalcopyrite structure. It was suggested that the strong interaction between excitons and optical phonons took place in obtained CuAlS2 powder.