Thermoelectric performance of p-type skutterudites Yb_xFe _4-yPt_ySb₁₂ (0.8 ≤ x ≤ 1, y = 1 and 0.5)

Thermoelectric performance of p-type skutterudites currently lags that of the corresponding n-type materials, and improvement of this important class of materials has become the focus of considerable research effort world-wide. Recent calculations find promising band structure features in p-type skutterudite materials of the type AFe₃NiSb₁₂ (A =Ca, Sr, or Ba), which could potentially lead to excellent thermoelectric properties. Recent work on the Yb-filled analogs of these formulations (YbFe ₃NiSb₁₂) however, finds that the onset of intrinsic conduction at lower than expected temperatures deteriorates the performance above 500 K. This leads to performance in the temperature range of interest for automotive waste heat recovery applications. We, therefore, seek a way to increase the band gap in order to find a way to minimize the deleterious effects of intrinsic conduction on thermoelectric performance. Here, we present ab initio band structure calculations, the synthesis and thermoelectric properties of Yb_xFe_4-yPt_ySb₁₂ (0.8 x 1, y 1 and 0.5). Ab initio calculations find that the band gap increases for YbFe ₃PtSb₁₂ as compared to the Ni-containing analog, though no such increase in the band gap energy was found for YbFe_3.5Pt _0.5Sb₁₂ as compared to YbFe_3.5Ni _0.5Sb₁₂. The y 1 sample shows a characteristic transition to intrinsic conduction with a decrease in the Seebeck coefficient at temperatures above 700 K. The increased carrier concentration in y 0.5 virtually eliminates any evidence of intrinsic conduction, and the Seebeck coefficients for these samples increase monotonically up to 750 K, resulting in power factors approaching 27 μW/cm·K² at 750 K. These power factors combined with low thermal conductivity result in a ZT = 0.9 at 750 K for Yb _0.95Fe_3.5Pt_0.5Sb₁₂.