Thermoelectric properties in Bi_2-xPb_xSr_3-yY_yCo₂O_9-δceramics

Abstract

Thermoelectric (TE) properties (resistivity and thermopower) of polycrystalline ceramics in the Bi2-xPbxSr3-yYyCo2O9-δ system prepared by a solid-state reaction in air have been investigated as a function of temperature up to about 300 K, changing the combination of x and y. These oxides are chemically very stable, and TE properties and the lattice structures do not change even after they are heated at high temperatures. Y doping has a profound effect in reducing resistivity. When y (the amount of Y) is small, ligand holes created by O 2p-Co 3d hybridization are mainly responsible for insulating conduction. With increasing y, resistivity decreases rapidly and insulating conduction transfers to metallic conduction. This is due to the shrinkage in the lattice constant by the Y doping, which leads to band crossing of the O 2p and Co 3d levels. Measurements of TE properties including thermal conductivity have been carried out on the material with x = y = 0.5 in the high-temperature range up to 800 K. The TE figure of merit increases from 2×10-5 K-1 to 7×10-5 K-1 as the temperature increases from 400 K to 800 K, which indicates that this compound has high potential as a good TE material at high temperatures.

Thermoelectric Properties (Resistivity and Thermopower) in (Bi1.5Pb0.5Ca2−MCo2O8− (M=Sc3+, Y3+, or La3+)

“…1 (11,14,15). In XRD pattern in each specimen, there are also satellite peaks due to impurity phases but they are very weak in comparison with Bi 2Àx Pb x Sr 3Ày Y y Co 2 O 9Àd (7). These results coincide with the description in the Introduction.…”

“…The volume fractions of these impurity phases are never negligibly small and moreover, these phases interfere with the elucidation of TE properties of the bulks in the ceramics specimen very seriously as described in our previous report (7). Ceramic compounds of a single phase are, however, rather easy to produce in ðBi; PbÞ 2 Sr 2 Co 2 O 8Àd -system (6,13 ions and their amounts, i.e., x: After being ground very carefully and mixed well, powders were pressed into pellets and sintered finally in air at 830-8501C for 12-18 h.…”

“…Bi 2Àx Pb x Sr 3Ày Y y Co 2 O 9Àd also involves high potential for a high TE figure of merit Z; as our previous report indicates (7). Since our previous study on Bi 2Àx Pb x Sr 3Ày Y y Co 2 O 9Àd mostly concentrated only on developing of a high temperature material with a high TE figure of merit (7), an elucidation to clarify the reasons for the concomitant emergence of low resistivity and high thermopower is now required.…”

High Temperature Superconductors REBa2Cu3O7 (RE=Y, Gd and Eu) For Possible Thermo-electric Applications

“…Of course, these values are much smaller than those observed in good thermoelectric. Iguchi et al [5] have investigated the TE properties of Bi2-xPbxSr3-yYyCo2O9-δ and have reported that such ceramics show an increase in Z value with increase in temperature.…”

Magnetic States of the Co-ions in Ca and Y Doped (Bi,Pb)2Sr2Co2O8 Thermoelectric Materials

“…In subsequent efforts to further explore new thermoelectric materials, both (Bi,Pb)-Sr-Co-O and (Bi,Pb)-Ca-Co-O compounds with additional doping of trivalent Y, and other trivalent elements (Sc,La), were reported to exhibit favorable temperature dependent electric transport behaviors [13,14]. However, no explicit information was offered on the spin state of Co 3+ and Co 4+ .…”