Crystal Structure and Transport Properties of the Homologous Compounds (PbSe)₅(Bi₂Se₃)_3m (m = 2, 3)

Selma Sassi (1) , Christophe Candolfi (1) , Gaëlle Delaizir (2) , Sylvie Migot (1) , Jaafar Ghanbaja (1) , Christine Gendarme (1) , Anne Dauscher (1) , Bernard Malaman (1) , Bertrand Lenoir (1)

1 IJL - Institut Jean Lamour
2 IRCER-AXE3 - IRCER - Axe 3 : organisation structurale multiéchelle des matériaux

We report on a detailed investigation of the crystal structure and transport properties in a broad temperature range (2–723 K) of the homologous compounds (PbSe)₅(Bi₂Se₃)_3m for m = 2, 3. Single-crystal X-ray diffraction data indicate that the m = 2, 3 compounds crystallize in the monoclinic space groups C2/m (No. 12) and P2₁/m (No. 11), respectively. In agreement with diffraction data, high-resolution transmission electron microscopy analyses carried out on single crystals show that the three-dimensional crystal structures are built from alternating Pb–Se and m Bi–Se layers stacked along the a axis in both compounds. Scanning electron microcopy and electron-probe microanalyses reveal deviations from the nominal stoichiometry, suggesting a domain of existence in the pseudo binary phase diagram at 873 K. The complex atomic-scale structures of these compounds lead to very low lattice thermal conductivities κL that approach the glassy limit at high temperatures. A comparison of the κ_L values across this series unveiled an unexpected increase with increasing m from m = 1 to m = 3, in contrast to the expectation that increasing the structural complexity should tend to lower the thermal transport. This result points to a decisive role played by the Pb–Se/Bi–Se interfaces in limiting κ_L in this series. Both compounds behave as heavily doped n-type semiconductors with relatively low electrical resistivity and thermopower values. As a result, moderate peak ZT values of 0.25 and 0.20 at 700 K were achieved in the m = 2, 3 compounds, respectively. The inherent poor ability of these structures to conduct heat suggests that these homologous compounds may show interesting thermoelectric properties when properly optimized by extrinsic dopants.

Mots clés: thermoelectricity; transport properties; crystal structure

Domaines: Matériaux; Cristallographie

Selma Sassi, Christophe Candolfi, Gaëlle Delaizir, Sylvie Migot, Jaafar Ghanbaja, et al.. Crystal Structure and Transport Properties of the Homologous Compounds (PbSe)₅(Bi₂Se₃)_3m (m = 2, 3). Inorganic Chemistry, 2018, 57 (1), pp.422-434. ⟨10.1021/acs.inorgchem.7b02656⟩. ⟨hal-02180362⟩