Raman spectra of Sr2Nb2O7 have been successfully obtained at temperatures up to 1643 K for the first time, using a continuous-wave ultraviolet Raman spectroscopic system designed to measure the Raman scattering from materials at high temperature. The Raman spectra of Sr2Nb2O7 with a symmetry of Cmc21 are described in terms of the parameter related to temperature variation at constant pressure, defined in a similar way to the Gruneisen parameter. By means of comparing vibrational modes of Sr2Ta2O7, the higher frequency modes located above 210 cm-1 are assigned to NbO6 internal modes. The parameter of NbO6 internal modes is as large as that of lattice modes, reflecting the weak chemical-bond strength of Nb–O bonds.
We report on the fabrication and characterization of AlGaN-based PiN type UV photodiodes with and without the surface recessed electrode structures. It was confirmed that the device with the surface recessed structure showed a much higher responsivity of 202 mA/W at a wavelength of 272 nm under a reverse bias voltage of -5 V than that of the device without the surface structure. This responsivity corresponds to external quantum efficiency as high as 92%.
In order to improve the electromagnetic properties of 80wt%NiCuZn + 20wt% CaCu3Ti4O12 composites, Co2O3 as an additive was studied in this work. The effects of Co2O3 content on the electromagnetic properties were investigated, which confirmed that permeability of composites was decreased and cut-off frequency was improved with Co2O3. The nonlinear fitting of permeability dispersion have revealed the relationships between domain wall resonance, spin rotation relaxion mechanisms, and local induced anisotropy, the existence of local induced anisotropy caused by ordering of Co ions could influence the initial permeability. Meanwhile, the dielectric constant was increased with the addition of Co2O3, and all the samples kept a lower tanδ，which was less than 0.01 at the frequency between 107Hz to 108Hz.
Higher superconducting transition temperature Tc is achieved in longer Cu-Cu bond distance samples. In this study, indium-based cuprate compounds with long Cu-Cu bond distance were prepared via solid-state reaction. The parent compound InBa2CuO4.44 is not electrically conducting due to the lack of oxygen ions in the CuO2 layer. In order to make it conducting, the oxygen content should be increased. For this purpose, polycrystalline InBa2-xLaxCuOy samples were prepared. In case of x = 1.0, single-phase compounds were prepared. Unfortunately, it is not superconductor but semiconductor.
We conducted the biotransformation of 4-chromanone and 4-chromanol using two kinds of fungi, Botrytis cinerea and Colletotrichum acutatum, as biocatalysts. The biotransformation of 4-chromanone using B. cinerea yielded 98.6% 4-chromanol by day 3. This chiral compound was identified as (R)-4-chromanol (76.4% yield) and its enantiomer excess was 52.8%ee. The reaction was accelerated by the addition of the coenzyme NADPH. In contrast, the same reaction using C. acutatum was initially slow but increased from days 3 to 8, as indicated by the gradual reduction in the substrate and increased production of 4-chromanol. No rapid change was observed from days 12 to 18. The reaction generated 4-chromanol at 86.0% yield after 28 days. Conversely, there was no evidence of a reverse reaction with either biocatalyst when 4-chromanol was used as the substrate. Mimicking similarly natural environmentally friendly methods would be useful for the synthetic production of natural compounds.
We report the synthesis of a photocatalytic composite of spherical porous hydroxyapatite (sHAp) and TiO2. sHAp was prepared by a wet method using simulated body fluid as a slurry and was then mixed with a TiO2 sol to obtain the sHAp + TiO2 composite. The TiO2 content of sHAp + TiO2 was ~7.8 wt. %. sHAp+TiO2 showed photocatalytic activity that was more than ten times greater than that of TiO2 even under irradiation with the low-intensity ultraviolet (UV) light of a fluorescent lamp. Mb decomposition of 58.2% was achieved under UV light with an intensity of 7.60 ×102 μW cm-2 using the sHAp + TiO2 composite, which is significantly higher than the 8.05% achieved using only TiO2. Thus, the composite material showed higher activity than that of unsupported TiO2. Furthermore, sHAp + TiO2 could oxidize leucocrystal violet (LCV) to crystal violet (CV) even after being placed in the dark for 120 h. The positively charged holes are suggested to persist on TiO2 because of the electron withdrawing effects of sHAp and can contribute to LCV oxidation. Thus, the photocatalytic activity of TiO2 was improved by using sHAp as a support.