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Thermoelectric properties of Sm-doped BiCuSeO oxyselenides fabricated by two-step reactive sintering

Among layered oxygen-containing compounds, BiCuSeO is one of the most promising candidates for thermoelectric applications due to its intrinsically low thermal conductivity and good thermal stability. However, the rather poor electrical conductivity of pristine BiCuSeO hinders its potential. Further enhancement of the thermoelectric performance by single doping at Bi site is limited mainly due to dramatic decrease of carrier mobility. Thus, new strategies, such as dual doping or doping with variable-valence elements seem to be promising. Along with that, the development of a fast and scalable synthesis route is essential for the industrial-scale fabrication of thermoelectric materials. Hence, in this paper, Bi$_{1-x}$Sm$_{x}$CuSeO samples (0 $\leq$ $x$ $\leq$ 0.08) have been synthesized with a simple and scalable reactive sintering process. For comparison, Bi$_{1-x}$Sm$_{x}$CuSeO oxyselenides were also obtained by the conventional solid-state route. Our results highlight that, Sm for Bi substitution increases the electrical conductivity by 1.5 - 2 times and decreases the Seebeck coefficient by ~1.4 times at 873 K for both series. Overall, considering the increase of lattice thermal conductivity upon doping and not optimized power factor, the figure of merit $zT$ is reducing upon doping.