Synthesis, crystal structure, and thermoelectric properties of layered antimony selenides REOSbSe₂ (RE = La, Ce)

Inspired by the recent first-principles calculations showing the high thermoelectric performance of layered pnictogen chalcogenides, we experimentally characterise the crystal structure and high-temperature transport properties of the layered antimony selenides REOSbSe₂ (RE = La, Ce). The crystal structure of REOSbSe₂ was the tetragonal P4/nmm space group, consisting of alternate stacks of SbSe₂ and REO layers. These two compounds were n-type semiconductors. The optical band gaps of LaOSbSe₂ and CeOSbSe₂ were evaluated to be 1.0 and 0.6 eV, respectively. The room-temperature thermal conductivity was 1.5 W m⁻¹ K⁻¹ for RE = La and 0.8 W m⁻¹ K⁻¹ for RE = Ce. These relatively low thermal conductivities were comparable to those of isostructural layered bismuth chalcogenides. We substituted O²⁻ with F⁻ ions to introduce electrons as charged carriers to optimize the thermoelectric performance, but increasing the electrical conductivity was still challenging. (author)