Thermoelectric properties of p-type skutterudites Yb _xFe _3.5Ni _0.5Sb ₁₂ (0.8 ≤ x ≤ 1)

p-Type skutterudites, with nominal compositions Yb _xFe _3.5Ni _0.5Sb ₁₂ (0.8 ≤ x ≤ 1), have been synthesized by induction melting with subsequent annealing, and their thermoelectric properties evaluated from 3.5 to 745 K to assess their suitability for thermoelectric-based waste heat recovery applications. We report results for the synthesis and measurements of Seebeck coefficient (S), electrical resistivity (ρ), thermal conductivity (κ), Hall coefficient (R _H) and effective mass (m/m ₀) of Yb _xFe _3.5Ni _0.5Sb ₁₂ (0.8 ≤ x ≤ 1). Powder X-ray diffraction and electron probe microanalysis show that this system has a narrow filling fraction range of x ∼ 0.84-0.86 for Yb in the crystallographic voids. All samples show positive R _H for the entire temperature range studied, with carrier concentrations ranging from 9.6 × 10 ²⁰ to 2.8 × 10 ²¹ cm ^-3 at room temperature. Relatively high values of S result in high power factors up to 17 μW cm ^-1 K ^-2 at room temperature. However, large values of κ and a sharp reduction in the S at high temperature due to bipolar conduction prevent the attainment of high thermoelectric figure of merit.