Patterns of effect of spark plasma sintering temperature on microstructure of thermoelectric composites based on Bi₂Te_2.1Se_0.9Bi₂ matrix with cobalt inclusions

Effect of spark plasma sintering temperature on the formation of Co filler particles in the Bi₂Te_2.1Se_0.9 matrix has been examined. Owing to high-temperature diffusion redistribution of atoms in the matrix and filler materials and chemical interaction between these materials, in the Bi₂Te_2.1Se_0.9 + 0.33 wt % Co, core–shell filler particles (Co@CoTe₂) are formed. With increasing the sintering temperature, fraction of the “CoTe₂ shell” in the particles increases, while fraction of the “Co core” decreases. This behavior is due to an increasing in the diffusion coefficient of Co in the Bi₂Te_2.1Se_0.9 matrix with increasing in the sintering temperature. The concentration profiles of the Co distribution of in the Bi₂Te_2.1Se_0.9 matrix, governed by diffusion, are well described using Fick’s second law for diffusion from a limited source of a diffusing substance. The diffusion coefficient of Co increases with increasing un the sintering temperature in accordance with the Arrhenius law and with an activation energy of ~0.61 eV.