Measurements of the dielectric constant κ in high-purity BaTiO3 ceramics as a function of temperature show that κ is quite dependent on grain size in the ferroelectric state while it is almost independent of grain size in the paraelectric state. In the ferroelectric orthorhombic and rhombohedral phases, κ decreases rapidly with lowering temperature when grain size is reduced smaller than 3 μm. It is also observed that the Curie temperature Tc is decreased very slightly, but the lower two transition points are shifted to higher temperatures as grain size decreases.

Discharge and charge characteristics of cathode‐active materials for lithium batteries were studied. Electron acceptors of charge transfer complex with high electron affinity were examined as cathode‐active materials because they were expected to have high cell voltage. These electron acceptors are 2,4,7‐trinitro‐9‐fluorenone (TNF), 2,4,5,7‐tetranitro‐9‐fluorenone, 7,7,8,8‐tetracyanoquinodimethane, 9,10‐phenanthrenequinone, and 13 other compounds. Among these compounds, TNF showed the highest discharge capacity (1050 A‐hr/kg) and the highest energy density (2030 W‐hr/kg). Cycle lives of TNF were 400 and 54 times at charge‐discharge capacity of 100 of A‐hr/kg (1.2 electron transfer per 1 mol TNF) and 200 A‐hr/kg (2.4 electron transfer per 1 mol TNF), respectively. The cycle tests indicate reversibility of TNF up to two‐electron transfer.

Discharge and charge characteristics of various phthalocyanine cathodes coupled with lithium metal are studied. The best capacity based only on cathode active material weight is 1440 A‐hr/kg in the lithium/iron phthalocyanine system, and the cycle life of the lithium/Cu phthalocyanine system is more than 100 times at the discharge depth of 157 A‐hr/kg. The cathode reaction mechanism is supposed to be lithium intercalation between phthalocyanine molecules. The results indicate that these phthalocyanines are promising cathode active materials for lithium secondary batteries.

The effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is <3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO3 ceramics. Lattice constant c decreases with increasing Dy concentration whereas a increases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO3 ceramics are cooled below Tc, strongly influences the effects of grain size.

Preliminary results of quantitative analysis of volcanic ash clouds observed over the Sakurajima volcano in Kagoshima, Japan, were obtained by using weather radar and surface instruments. The Ka-band Doppler radar observations showed the inner structure of a volcanic ash column every two minutes after an eruption. Operational X-band polarimetric radar provides information on three-dimensional ash fall amount distribution. The terminal fall velocity of ash particles was studied by using optical disdrometers, together with the main specifications of observation instruments.

No abstract

No abstract

No abstract