Thermoelectricity is defined as the conversion of thermal energy to electrical energy.  We propose complex anisotropic structures based on heavy elements have high potential for thermoelectric properties.  Previously, K2RE2Bi2Se9 compounds (RE=La, Ce, Nd, Yb) were synthesized via a molten flux synthesis. The structural analysis revealed a symmetry reduction in space group from Pbam to P212121 as the size of the rare earth element becomes smaller.  The oxidation states were hypothesized to be K2+RE23+Bi23+(Se2-)5(Se22-)2 based on crystallography. X-ray photoelectron spectroscopy (XPS), however, indicated the presence of Bi+3 and Bi+5. We proposed bismuth disproportionate into +3/+5 oxidation states. SQUID magnetic measurements on K2Ce2Bi2Se9 show temperature independent paramagnetism, which could be due to the promotion of the bismuth 6s electrons into the conduction band, which would make these compounds intrinsic n-type semiconductors. The work lead to the synthesis of a new quaternary rare earth pnictogen telluride, K(RE)Pn2Te6 (RE=La, Ce, Nd; Pn=Bi, Sb).  The Sb analog has formed highly pure metallic crystals that would be suitable for resistivity and Seebeck coefficients measurements to study the thermoelectric properties.

New potassium rare-earth pnictogen chalcogenides with potential thermoelectric properties

248th National Meeting (2014)

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