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Bi 2 Sr 2 Co 2 O y ceramic samples have a structure similar to phonon glass electronic crystals, and their thermoelectric properties can be effectively adjusted through repeated grinding and sintering. The results show that multi-sintering can make their grain refined and increase their grain boundary, which will effectively increase density and phonon scattering. Finally, multi-sintering can reduce the resistivity and thermal conductivity, thus obviously improve thermoelectric figure of merit (Z T) of Bi 2 Sr 2 Co 2 O y . The optimum Z T value of 0.26 is achieved at 923 K by the third sintered sample. [ABSTRACT FROM AUTHOR]

Grains, grain boundaries, magnetic domain distributions, and their correlations in Fe81Ga19 alloys as-cast, annealed, and under compressive and grinding stresses were investigated using scanning electron acoustic microscopy (SEAM) and magnetic force microscopy (MFM). For as-cast and annealed samples, the main domain structure obtained using SEAM is not clear. For samples under stresses, the main domains are obvious and regular. For the sample under compressive stress, its stripe domains array orderly and perpendicularly to the stress direction. The subdomains of as-cast sample observed using MFM show a clear dendritic structure. However, for the sample under compressive stress, the subdomains are irregular. These results may be helpful to understand the magnetostrictive behavior of Fe–Ga alloys under stress. [ABSTRACT FROM AUTHOR]

Contrast origin of magnetic domain structure imaged by scanning electron acoustic microscopy (SEAM) is studied by analyzing qualitatively the interaction between an incident electron beam and a sample. Some parameters related to the acoustic signal detected by a piezoelectric transducer are obtained through solving a vibration equation. Contrasted with magnetic domain structures of Terfenol-D and Fe81Ga19 alloys obtained by SEAM in linear and nonlinear (second harmonic) modes, imaging mechanism of magnetic domains is attributed to piezomagnetic coupling mechanism, magnetostrictive coupling mechanism, and thermal-wave coupling mechanism. [ABSTRACT FROM AUTHOR]

The oscillations of excitonic and nuclear spin polarizations in an optically pumped single self-assembled In0.8Al0.2As/Al0.35Ga0.65As quantum dot (QD) were clearly observed under the excitation of a wetting layer edge at B=5 T. This indicates that an exciton pair with opposite spins is alternatively created via the half-localized state only by changing the delay time between cross-linearly polarized pulse pair. Furthermore, periodic modulation of Zeeman energy synchronizes the degree of circular polarization of photoluminescence from a single QD, indicating that the Overhauser field follows the optically created electron spin polarization in half-localized states of a QD, and the half-localized state in a QD consists of a confined electron in a discrete state and hole in the continuum state. [ABSTRACT FROM AUTHOR]

Cu1.98−xNaxSe nanopowders were synthesized using a hydrothermal method and hot-pressed into bulk pellets to assess the effects of Na doping on the thermoelectric properties of Cu1.98Se. The original layered microstructure was maintained at low doping levels, although nanopores, together with point defects, appeared to decrease the thermal conductivity. The thermoelectric properties of the material were improved by Na doping, resulting in a maximum ZT value of 1.32 for Cu1.94Na0.04Se at 973 K. The experimental data indicate that an optimal level of Na doping effectively improves the thermoelectric performance of non-stoichiometric Cu1.98Se. [ABSTRACT FROM AUTHOR]

The nanopowders of Cu2Se were synthesized by the hydrothermal method, and then were hot-pressed into bulk pellets. The effects of different preparation conditions on the structure and thermoelectric properties of Cu2Se nanocrystalline bulk alloys were investigated. The resistivity and Seebeck coefficients increase with the increment of hot-pressing temperatures, while they decrease with the increment of hot-pressing time, except for the Seebeck coefficients of the sample hot-pressed for 30 min. Based on the power factors and dimensionless thermoelectric figure-of-merit (ZT) values, the optimum hot-pressing parameters are 700°C and 30 min. [ABSTRACT FROM AUTHOR]

Presents a study which measured room-temperature photoluminescence spectra using a two-band structure from porous silicon (PS) as a function of excitation wavelengths. Details of experimental techniques used; Assumption of the quantum confinement/luminescence centers model.

The Na doping effects on the high temperature thermoelectric properties of ( = 0, 0.05, 0.10, 0.15, 0.20 and 0.30) ceramics were investigated from 343 K to 973 K. When , the electrical resistivity of decreases with increasing Na doping amount due to the hole-doping effect, which exhibits metallic electrical conductivity behavior. While, at the temperature range of 480-830 K, the samples with exhibit semiconductor electrical conductivity behavior instead. The Seebeck coefficients are improved by Na doping at lower temperature, but they decrease slightly at higher temperature except for . Roughly, the thermal conductivity is depressed by the doping defects. As an overall result, the dimensionless figure of merit of reaches the maximum value of 0.3 K at 973 K, which is nearly twice the value of the undoped sample . [ABSTRACT FROM AUTHOR]

The influence of ion sizes on the electrical resistivity, Seebeck coefficients, thermal conductivity and values of prepared by the solid-state reaction method was investigated from 373 K to 973 K. The electrical resistivity decreases with decreasing ion sizes. Both the electrical resistivity and the Seebeck coefficients have a transition at about 630 K. Especially, the transition phenomenon disappears gradually with decreasing ion sizes, and is attributed to the oxygen adsorption of . The values increase with rising temperature or decreasing ion sizes. The with the smallest size has the maximum value that reaches 0.1 at 973 K. [ABSTRACT FROM AUTHOR]