Single-Phase Ba 2 Ti 9 O 20 Fabricated after Addition of 5% B 2 O 3
- PDF / 806,312 Bytes
- 1 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 192 Views
material film and the SiO2 /Si interface. The researchers said that the interface causes this behavior in two ways. First, the interface reflects some of the PL radiation, producing constructive and destructive interference between the directly emitted and reflected radiation. The PL intensity increases (and lifetime decreases) for samples in which the thickness of the SiO 2 layer allows mostly constructive interference. The opposite is true when destructive interference predominates. Second, the interface causes a damped oscillatory fluctuation in the local density of the optical modes that, in turn, has the same effect on the PL intensity and lifetime. This semiconductor-interfaceinduced optical-mode density fluctuation has been predicted by quantum mechanical calculations and previously observed for single-atom emitters. GREG KHITROV
Single-Phase Ba2Ti9O20 Fabricated after Addition of 5% B2O3 The compound Ba2Ti9O20 is known for its good microwave properties, including a high-dielectric constant. Synthesis of Ba2Ti9O20 by solid-state reaction is a challenging procedure because of the likelihood of the formation of intermediate stable compounds and of decomposition in different phases. Different techniques have been developed to obtain singlephase Ba 2Ti 9O 20, including the use of solid-state additives, chemical methods such as sol-gel fabrication, and the addition of precursors. Among other additives, B2O3, known for improving dielectric properties and optimizing sintering conditions in other materials, is a common addition in electronic glass applications. For these reasons, it was chosen by a group of scientists from the National Taipei University of Technology and the National Taiwan Ocean University as a solid-state additive in the fabrication of Ba2Ti9O20, as they described in the June issue of the Journal of the American Ceramic Society. S.-F. Wang of Taipei and co-workers started the fabrication of Ba2Ti9O20 from powders of 81.8% TiO2 and 18.2% BaO. After mixing in methyl alcohol for 6 h, the powders were dried and then calcined at 1000°C for 8 h. At this point, x-ray diffraction (XRD) analysis detected two phases: BaTi4O9 and BaTi5O11. Powders were then mixed again with different additions of Ba2O3 in methyl alcohol for 8 h. Further mixing with 3.5 wt% of a 15% poly(vinyl alcohol) solution allowed the fabrication of disks that were later sintered at different temperatures for 6 h. A liquid-displacement method permitted the measurement MRS BULLETIN/AUGUST 2002
of the density of the resulting materials. Powders with 5% addition of Ba 2 O 3 showed a higher density after sintering at temperatures below 1100°C, as compared with the material without additive. Results after differential thermal analysis show that the material with 5% Ba2O3 has an endothermic peak at 840°C. At this temperature, Ba2O3 forms a liquid eutectic that enhances the densification process. At temperatures higher than 1100°C, evaporation of Ba2O3 precludes the increasing densification, as compared with the material without Ba2O3 additio
Data Loading...
