Exotic reinforcement of thermoelectric power driven by Ca doping in layered Bi2Sr2-xCaxCo2Oy

We have systematically investigated thermoelectric properties of layered Bi2Sr2-xCaxCo2Oy (0.0 <= x <= 2.0) by a series of Ca doping. The resistivity presents a metal-insulator transition for lightly doped samples, while such behavior is not observed for heavily doped samples. Amazingly, the Ca doping induces an exotic reinforcement of thermoelectric power S in the whole x range. In particular, the Sommerfeld coefficient is dependent on carrier density and also as a function of density of states at the Fermi level which is responsible to the persistent enhancement of large S. Moreover, thermoelectric performance can be effectively modulated by temperature control. (C) 2013 AIP Publishing LLC.