Thermoelectric Properties of Dual Doped Bi2Sr2Co2Oy-Based Ceramics

We have investigated the crystal structure and high temperature thermoelectric properties of polycrystalline Bi2–2xNa2xSr2Co2−xWxOy (0 ≤ x ≤ 0.075) samples. Powder x-ray diffraction data show that all samples are phase pure consisting of misfit-layered structure of alternately stacked hexagonal CoO2 and double rock-salt BiSrO2 layers. It is found that dual doping of Na and W in Bi2Sr2Co2Oy system is fairly effective in improving the thermoelectric properties owing to simultaneous decrease of electrical resistivity (ρ) and thermal conductivity (κ) of samples. All samples exhibit a large Seebeck coefficient (S), which seems not to be affected by the level of doping. As a result, a very high power factor (PF) of 2.82 × 10−4 W/m K2 has been obtained for x = 0.025 sample at 1000 K. The corresponding dimensionless figure of merit (zT) for this sample has been determined to be 0.35 at 1000 K, which is ∼ 2.2 times higher than zT value of the pristine sample providing a promising class of material for high-temperature thermoelectric applications.