Papers by Author: Yoshikazu Shinohara

Abstract: Laser medium for solar-pumped solid laser of 10MW-1GW power is a key to realize Laser Space Solar Power System (L-SSPS). Since it is an ultrahigh power system operated in space, the laser medium must satisfy the conditions such as high efficiency, high power per weight or volume, excellent durability and maintainability, thermal equilibrium operation, and excellent long-range propagation of oscillated laser. YAG (Y3Al5O12) ceramics doped doubly with Nd and Cr is considered to be a suitable laser medium for L-SSPS at present. There are the following important points for L-SSPS application: 1) Optimization of the doping amount, 2) Process, 3) Temperature control. Feasibility of YAG ceramics is discussed from a view point of material science and proposed a YAG ceramics structure with graded distribution of dopants.

Abstract: The concept of environmental conscious materials, ecomaterials, is reviewed. It has dispersed and recognized in the world as contributing to a sustainable society. Advanced models for secondary materials utilization, environmental benign processes and new material recycling systems are introduced.

Abstract: Typical conductive polymers of poly(3-alkylthiophenes) were synthesized by oxidative polymerization. Polythiophene with no side chain was also electrolyticaly polymerized. Alkyl side chains were CnH2n+1 with n=4, 6, 8, 12. The regioregularity with the HT linkage was larger than 99% based on NMR analysis. We have evaluated the effect of side chain size on the thermoelectric properties of Seebeck coefficient and electrical conductivity. The results were as follows: 1) Seebeck coefficient decreased with an increasing electrical conductivity. 2) High Seebeck coefficient >1mV/K was observed at low electrical conductivity <10-2S/cm. 3) Small side chains, especially no side chain caused higher thermoelectric properties of polythiophene series.

Abstract: In this paper, we reported that lead telluride (PbTe) with continuous carrier concentration gradient, in which PbI2, Al and Zr were doped, were successfully fabricated by the unidirectional solidification method. The carrier concentration was optimized by adjusting the relation between the dopants and the carrier concentration gradient. The carrier concentration for the ingots was estimated from the resistance results which were measured by the one-probe method. The result shows that the carrier concentration was large at the initiation side and small at termination side of the solidified ingots. The degree of the carrier concentration gradient can be controlled by the holding time at a liquid state and the cooling rate from the liquid state. The carrier concentration gradient can be largely affected by the Al-dopant. The samples 0.07mol%PbI2-0.05mol%Zr-0.07mol%Al-PbTe, which were made from a liquid phase at 1200K held for 1h and cooled at 98K/h, showed a carrier concentration gradient ranging from 2×1024 to 1.5×1025 /m3. The effective maximum power for this continuous FGM is 20% larger than that of jointed FGM.

Abstract: Typical conductive polymers of poly(3-alkylthiophenes) were synthesized by oxidative polymerization. Alkyl side chains were CnH2n+1 with n=4, 6, 8, 12. The regioregularity with the HT linkage was larger than 99% based on NMR analysis. Completely regioregular head-to-tail (HT) poly(3-alkylthiophenes) were obtained. We have evaluated the effect of side chain size on the thermoelectric properties of Seebeck coefficient and electrical conductivity. The results were as follows: 1) Seebeck coefficient decreased with an increasing electrical conductivity. 2) High Seebeck coefficient >1mV/K was observed at low electrical conductivity <10-2S/cm. 3) The small side chain caused the higher electrical conductivity in the range of electrical conductivity <10- 1S/cm.