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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]

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]

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]