We simulate Nernst generation system with using the theory on thermo-electro-magnetic phenomena and the measured data of sintered Bi2Te3 semiconductors. Now, this is the one-dimensional analysis. As a result, it was shown that the performance of Nernst generation system was well improved by using the thermal difference at low temperature near liquid nitrogen temperature.
A new class of thermoelectric materials, skutterudites and filled skutterudites, has become a topic because the materials have a dimensionless thermoelectric figure of merit ZT of 1 at 800K. Skutterudites are binary semiconducting compounds with the general formula MX3 (where M is Co, Rh, Ir; and X is P, As Sb). Within these materials, the three isothermal antimonides such as IrSb3, RhSb3, and CoSb3 exhibit excellent electronic transport properties, including a high value of the hole mobility (8000cm2/Vs). For example, p-type CoSb3 has a hole mobility value of 3000cm2/Vs at room temperature, and ZT of Pd/Pt-doped CoSb3 is 0.85. Filled skutterudite alloys with the general formula of RM′4X12, where R is La, Ce, Pr, Nd or Eu and M′ is Fe, Ru or Os, are particularly interesting, because formally they are isoelectric (that is, have the same number of valence electrons per unit cell) with the binary skutterudites such as CoSb3. Relative to CoSb3, the filled skutterudites exhibit a remarkable factor-of-ten decrease in the lattice thermal conductivity, which reaches a value at room temperature equal to that of vitreous silica (SiO2). This is believed to be due to the “rattling” effect of the rare earth atoms that scatters the heat-carrying phonons. For example, CeFe3CoSb12 or LaFe3CoSb12 has a low lattice thermal conductivity value of about 0.015W/cmK at near room temperature.
Double doping of Pd and Pt in the skutterudite CoSb3 as donor impurities has been studied to produce a prominent effect on improving the thermoelectric figure of merit values. The double doping was found to have a beneficial effect on increasing the carrier concentration, causing a large increase of electrical conductivity as compared with that for the single doping of Pd or Pt. The electrical conductivity of about 2000 S/cm was obtained at room temperature for hot-pressed samples with Pd and Pt of 5 atomic per cent (Co0.9Pd0.05Pt0.05Sb3). In addition, the double doping significantly affected the lattice thermal conductivity, resulting in a large reduction of thermal conductivity to 0.05W/cmK. As a result, the dimensionless thermoelectric figure of merit reached about 0.85 at 800K.
The thin film growth of CoSb3 on a GaAs(100) substrate (the resistivity: 107Ωcm) was made by using magnetron rf-sputtering, and the electrical and thermoelectric properties of the films were studied with relation to annealing temperature and film thickness. Polycrystalline films with the skutterudite structure were successfully grown on the GaAs (100) substrate. The obtained films were found to be p-type, and their hole mobility, electrical conductivity, and Seebeck coefficient depended significantly on the annealing temperature and the thickness. The Seebeck coefficient of 600μV/K, which is about three times as large as that for a p-type single crystal, was obtained for the thin film annealed at 750°C with thickness of 71nm, and the power factor reached about 2×10-4 Wcm-1K-2.
Thick films of Bi2Te3 system thermoelectric materials were prepared by printing processes, and thermoelectric cooling modules were also prepared using the n- and p-type films. Seebeck coefficients and electric conductivities of the films increased up to sintering temperatures of 470-500°C, and showed the maximum values at the temperatures. The values of thermoelectric properties decreased over 470-500°C, which are related with microcrucks and reduction of the amount of Te in the films. The maximum values of the Seebeck coefficients of the films were similar to those of the corresponding bulk elements. The electrical conductivities of the films, however, were lower than the bulk elements. The microcrucks in the films caused the reduction of the conductivities. The thermoelectric properties of the modules corresponded with those of the n- and p-type thick films.
Si-Ge elements and Mo electrodes were tried to braze with 4 kinds of Ti-base brazes. Aπ-shaped module used for thermoelectric generator was constructed from one couple of p and n-type Si-Ge elements and Mo electrodes. The maximum electrical power Pmax and the internal resistivity Rin of the modules were evaluated as a function of temperature difference between the hot side and cold side of the module. The module using TZCN braze (TZCN-module) showed the highest Pmax and the lowest Rin After annealing treatment at 700°C in vacuum for 5hr, the Rin of the TZCN-module was increased to 1.5-2 times of the initial value before annealing. After the first 5hr annealing, the Rin was found to be stable for 53hr. Before and after annealing treatment at 700°C in vacuum for 3hr, the optical and the X-ray images of Si-Ge/Mo joint section brazed with TZCN were not observed to be changed. We thought that the increase of Rin during the first 5hr annealing is due to the fine cracks between Si-Ge and brazing layer.
Oxidation of contaminants in air and water was achieved by immobilized photocatalysts irradiated with low-intensity UV light which is inexpensive and poses less human health risk. Tiles and glass coated by TiO2, which are applicable as building materials, have the ability to kill E. coli and other bacteria and to break down foul odor, stains, endotoxin of E. coli under irradiation at low intensity. Photocatalytic oxidation of 3-chlorophenol was also achieved using a ceramic honeycomb coated with TiO2 powder in the circulated flow system under the irradiation at the intensity of 1.7mW/cm2 at 360nm of light wavelength.
The magnetic field strength is calculated numerically for three types of coils, i.e., a cylindrical, a cubic and a wave-like coils. It is possible from the calculated results to test whether each coil meets two requirements of the coil winding which is free from the magnetic force and the configuration of coil winding for providing the high β value or not. The cylindrical coil fulfills the requirement of coil winding which is free from the magnetic force, while the cubic coil fulfills the requirement of providing high β. It should be stressed that the port distorts markedly the initially intended magnetic field.
The formation and decomposition of metal hydrides can be described by reaction models with one rate determining partial step. The rate and time laws derived depend on the individual partial process which is considered to be rate determining. Relevant formulas are compiled in this paper and compared with experiments performed with LaNi4.7Al0.3 and Mg(Ni) powder samples.
The duality transformation is applied to the anisotropic charged layered XY lattice model (ACLXY model) that can be considered as the model of the high Tc superconducting Oxide. We derive the dual ACLXY model which is the dual representation of the ACLXY model and the disorder field theory which is the dual version of the anisotropic charged Lawrance-Doniach model. The disorder transition temperature as a function of the dual transition temperature is evaluated using the numerical calculation.
A good quality of Zn2SiO4:Mn phosphors were prepared by the solid state reaction method using MnCO3 as activators. The luminance properties, color purity and crystalline qualities were investigated as a function of the heating temperature and activator concentrations. In the Mn doping range from 0.005 to 0.15(g-atom/mol) in Zn2SiO4:Mn, the phosphors doped with Mn concentration of 0.08(g-atom/mol) showed the highest intensity of emission spectra and good color purity at the heating temperature of 1300°C for 4hrs under N2 atmosphere. The CIE chromaticity diagram showed that the more saturated color could be obtained for the phosphors with the Mn concentration of 0.08(g-atom/mol). As the Mn content increased, the maximum of emission spectra shifted slightly toward longer wavelength. From the SEM micrograph, it was found that the phosphors were composed of a great number of small grains about 3-8μm. The XRD analysis showed the typical rhombohedral crystal structure.