Evolution of the thermoelectric performance in low Ca-doped layered cobaltite Bi2Sr2Co2Oy

• Published in: Solid state communications 2013-03, Vol.158, p.16-19
• Main Authors: Yin, L.H., Ang, R., Zhao, B.C., Huang, Y.N., Liu, Y., Tan, S.G., Song, W.H., Sun, Y.P.
• Format: Article
• Language: English
• Subjects: A. Cobaltite; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity phenomena in semiconductors and insulators; D. thermoelectric; Electronic transport in condensed matter; Exact sciences and technology; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Physics; Saturation moments and magnetic susceptibilities; Thermoelectric and thermomagnetic effects
• ISSN: 0038-1098; 1879-2766
• DOI: 10.1016/j.ssc.2013.01.002

We have synthesized a series of layered cobaltite Bi2Sr2−xCaxCo2Oy (0≤x≤0.3). Reduced resistivity was observed with x≤0.2 due to the possible chemical pressure induced charge transfer between the Bi2Sr2O4 layer and CoO2 layer. Enhanced thermoelectric power S was also observed in the Ca-doped samples with the largest S as for x=0.2. The variation of S(T) could reflect the change of electronic correlation or the modification of local density of states and band structure near the Fermi energy. In addition, magnetic measurements show that the samples with x=0.0 exhibit abnormal and abrupt changes, revealing a possible thermally excited spin-state transition. It is found that the thermoelectric performance is obviously enhanced by the low Ca-doping. ► Reduced resistivity was observed in low Ca-doped Bi2Sr2Co2Oy. ► Enhanced thermopower and ZT was observed in low Ca-doped Bi2Sr2Co2Oy. ► A possible thermally excited spin-state transition was found in Bi2Sr2Co2Oy.