Thermoelectric Properties Of Compounds Research Articles

Electric Power Sources Based on the Seebeck Effect of Manganese Sulfides with Rare Earth Substitution

The thermoelectric properties of compounds with variable valence Mn1-ХReХS (0 ≤ X ≤ 0.2) in the temperature range of (80 – 1100) K are studied. The maxima on the temperature dependences of the Seebeck coefficient (thermal EMF) for all substitution concentrations and the change of the sign of the Seebeck coefficient from positive to negative with an increase in the substitution concentration in Mn1-XYbXS are determined. A model of impurity donor 4f-states is proposed and a satisfactory agreement with the data on the thermal EMF is obtained.

Thermoelectric Properties of Bi2 –xLuxTe2.7Se0.3 Solid Solutions

The thermoelectric properties of compounds based on Bi2 –xLuxTe2.7Se0.3 solid solutions with x = 0, 0.05, 0.1, and 0.2 are studied. The samples for investigations are prepared by chemical-solution deposition (to synthesize the initial powders) and spark plasma sintering (to obtain bulk samples). The patterns of changes in the electrical resistivity, Seebeck coefficient, and total thermal conductivity of the samples are determined as a function of the lutetium content. It is established that the optimal combination of these thermoelectric characteristics is attained for the composition with x = 0.05, which demonstrates the highest thermoelectric figure of merit (ZT ≈ 0.9 in the temperature range of 400–480 K) among all the studied compositions.

Phase diagram, crystal chemistry and thermoelectric properties of compounds in the Ca–Co–Zn–O system

In the Ca–Co–Zn–O system, we have determined the tie-line relationships and the thermoelectric properties, solid solution limits, and structures of two low-dimensional cobaltite series, Ca 3(Co, Zn) 4O 9− z and Ca 3(Co,Zn) 2O 6− z at 885 °C in air. In Ca 3(Co,Zn) 4O 9− z , which has a misfit layered structure, Zn was found to substitute in the Co site to a limit of Ca 3(Co 3.8Zn 0.2)O 9− z . The compound Ca 3(Co,Zn) 2O 6− z ( n=1 member of the homologous series, Ca n+2 (Co,Z n ) n (Co,Zn)′O 3 n+3− z ) consists of one-dimensional parallel (Co,Zn) 2O 6 6− chains that are built from successive alternating face-sharing (Co,Zn)O 6 trigonal prisms and ‘ n’ units of (Co,Zn)O 6 octahedra along the hexagonal c-axis. Zn substitutes in the Co site of Ca 3Co 2O 6 to a small amount of approximately Ca 3(Co 1.95Zn 0.05)O 6− z . In the ZnO–CoO z system, Zn substitutes in the tetrahedral Co site of Co 3O 4 to the maximum amount of (Co 2.49Zn 0.51)O 4− z and Co substitutes in the Zn site of ZnO to (Zn 0.94Co 0.06)O. The crystal structures of (Co 2.7Zn 0.3)O 4− z , (Zn 0.94Co 0.06)O, and Ca 3(Co 1.95 Zn 0.05)O 6− z are described. Despite the Ca 3(Co, Zn) 2O 6− z series having reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical resistivity values of its members are too high to achieve high figure of merit, ZT.

Phase compatibility and thermoelectric properties of compounds in the Sr–Ca–Co–O system

Two low-dimensional cobaltite series in the Sr–Ca–Co–O system have been investigated for their solid solution limit, structure, and compatibility phase relationships (850 °C in air). Thermoelectric properties have been measured for selected members of these solid solutions. In (Ca,Sr)3Co4O9, which has a misfit layered structure, Sr was found to substitute in the Ca site to a limit of (Ca0.8Sr0.2)3Co4O9. Compounds in the homologous series, An+2ConCo′O3n+3 [where A=Sr, Ca, (Ca,Sr), or (Sr,Ca)], consist of one-dimensional parallel Co2O66− chains that are built from successive alternating face-sharing CoO6 trigonal prisms and “n” units of CoO6 octahedra along the hexagonal c-axis. In the Can+2ConCo′O3n+3 series, only the n=1 phase (Ca3Co2O6) could be prepared under the present synthesis conditions. Sr substitutes in the Ca site of Ca3Co2O6 to a limit of (Ca0.9Sr0.1)3Co2O6. In the Srn+2ConCo′O3n+3 series, Ca substitutes in the Sr site of the n=2, 3, and 4 members to a limit of (Sr0.7Ca0.3)4Co3O9, (Sr0.67Ca0.33)5Co4O12, and (Sr0.725Ca0.275)6Co5O15, respectively. While the members of the Can+2ConCo′O3n+3 and Srn+2ConCo′O3n+3 series have reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical conductivity needs to be increased in order to achieve high ZT values.