N형 Skutterudite-나노카본 복합체의 열전 특성

Abstract

We report the effect of incorporation nanocarbone (NC) or porous nanocarbone (PNC) on thermoelectric properties in n-type skutterudite Yb0.2Co4Sb12 compound (N-SKD). The N-SKD powder was prepared by a combination of induction melting and melt-spinning processes. A high-energy ball milling process was employed to disperse the NC or PNC on the N-SKD powder, and then bulk composites (N-SKD/x wt% NC, PNC, x = 0.01 ~ 0.1) were prepared using spark plasma sintering (963 K, 50 MPa, 15 min). It was confirmed that the carbon additives were uniformly distributed in the composite by microstructural characterization. In the N-SKD/x wt% NC composites, the electrical conductivity (σ) exhibited a decreasing trend with increasing the NC content, while the Seebeck coefficient (S) increased. This behavior was attributed to the low-energy charge carrier filtering effect by introducing an energy barrier at interfaces between N-SKD and NC. The decrease in the carrier concentration by incorporating NC led to an increase in mobility, contributing to the optimization of the power factor. The maximum power factor (S2σ) of 47.9 x 10-4 W/mK2 was achieved at 664 K for the N-SKD/0.01 wt% NC composite. Moreover, the electronic thermal conductivity of the N-SKD/NC composites was effectively reduced due to the decrease in electrical conductivity. As a result, N-SKD/0.01 wt% NC composite exhibited a maximum ZT of 1.35 at 762 K. Additionally, we introduced porous structure into NC and fabricated the N-SKD/0.01 wt% PNC composite showing comparable electrical properties to the N-SKD/0.01 wt% NC composite. The N-SKD/0.01wt% PNC composite showed reduced lattice thermal conductivity by enhancing phonon scattering at porous structures in NC, achieving a maximum ZT of 1.5 at 716 K. Furthermore, the peak ZT in the composites moved toward the mid-temperature range (~523 K) by controlling carrier concentration. The SKD composite incorporating nanocarbon materials has been identified as a promising strategy for enhancing thermoelectric performance in the mid-temperature range.