Improved Synthesis Method and Thermoelectric Properties of the YbCuSb Zintl Phase

YbCuSb was synthesized via an improved quasi-solid-state synthesis method for this compound using either an open carbon crucible or a sealed stainless steel crucible. The former crucible led to a total fraction of secondary phases of 25% whereas the latter one led to less than 2% of secondary phases. Densification was performed by spark plasma sintering to reach relative density values larger than 94%. These densified YbCuSb samples are air- and water-stable at room temperature. Combined electronic transport measurements and ab initio electronic structure calculations led to the conclusion that YbCuSb is a semiconductor and can be classified as a Zintl compound. The present samples showed p-type conduction with large values of electronic mobility (78 cm2 V–1 s–1 at 300 K) and a small density of states effective mass (0.4 m0, with m0 the bare electron mass). They also displayed small values of Seebeck coefficient (9–14 μV K–1 at 300 K) and power factor (0.04–0.07 mW m–1 K–2 at 300 K) due to too large hole concentrations (2.9–7.6 × 1020 cm–3). The lattice thermal conductivity was small (λL = 1.5 W m–1 K–1), as expected from the overall trend in the ACuSb series (A = Ca, Sr, Ba, Eu, and Yb) and from the heavy atomic mass of Yb. Nonetheless, the modest values of power factor led to small values of thermoelectric figure of merit: maximum ZT = 0.09 at 700 K.