Optimization of thermoelectric properties in layered Bi2Sr2Co2Oy via high-magnetic-field sintering

Herein, we report the effect of the high-magnetic-field (HMF) sintering on the structural, electrical and thermal transport properties of the layered Bi2Sr2Co2Oy. Based on the results of x-ray diffraction and microtopography, we find the grains prefer to the oriented growth along the direction of applied magnetic field, leading to a higher textured degree and anisotropy. Correspondingly, the in-plane conductivity increases while the out-of-plane one reduces with increasing sintering magnetic field. At the same time, the in-plane thermopower shows an obvious enhancement after the HMF sintering, which mainly originates in the spin state transition of Co4+ ions. As a result, a remarkable enhancement of the in-plane thermoelectric figure-of-merit is obtained in the sample after the HMF sintering (8 T).