Thermoelectric powers (TEPs) of the pristine (Bi,Pb)2Sr2Can-1CunO 2n+4+δ(n=2 and 3) compounds and their iodine intercalates were measured as a function of temperature, in order to investigate the effect of intercalation on the conduction mechanism of the host compounds. From the comparative measurements, it is revealed that the iodine intercalation gives rise to different evolution of TEP depending upon the host lattice, i.e., a downward shift for Bi2Sr2CaCu2O8+δand an upward shift for Bi2-xPbxSr2Ca2Cu3O 10+δ. In order to elucidate an origin of such contrasting TEP behaviors in both intercalates, the evolution of electronic structure upon intercalation has been examined by performing the systematic micro-Raman and X-ray absorption near edge structure (XANES) analyses. According to the Raman and I LI-edge XANES studies, it is found that there is a partial electron transfer from host lattice to guest layer that is the same for both intercalates, which is in contrast with their opposite shifts of TEP. The present Cu K- and Bi LIII-edge XANES results also indicate the cooxidation of CuO2and BiO layers for both intercalates, whereas the Pb LIII-edge XANES analysis makes it clear that the Pb+IVion in Bi2-xPbxSr2Ca2Cu3O 10+δis completely reduced to Pb+IIion upon intercalation, leading to a decrease of hole contribution to TEP and consequently to an upward shift of TEP. From the present experimental findings, it becomes clear that a simple application of the universal plot of TEP (300 K) vs hole density may result in an inaccurate estimation of the oxidation state of CuO2layer.
Bibliographical noteFunding Information:
This work was supported in part by the Ministry of Education (BSRI-97-3413) and by the Korean Science and Engineering Foundation through the Center for Molecular Catalysis. Our thanks are extended to Prof. Y. W. Park for TEP measurements.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry