Novel n‐type Zintl phase thermoelectric materials: The Ca5−xRExAl2Sb6 (RE = Pr, Sm) system

Abstract

AbstractTwo novel n‐type Zintl thermoelectric materials of Ca4.97(1)Pr0.03Al2Sb6 and Ca4.94(2)Sm0.06Al2Sb6 were synthesized with the addition of two types of trivalent rare‐earth metals dopants and characterized by powder and single crystal x‐ray diffraction analyses. Two title compounds adopted the orthorhombic Ca5Ga2As6‐type phase and contained seven crystallographically unique atomic positions including one particular Ca/Pr or Ca/Sm mixed‐site. The crystal structure can be described as a combination of the one‐dimensional (1D) infinite chains and the cationic elements in between the 1D chains. Electrical transport property measurements proved that Ca4.97(1)Pr0.03Al2Sb6 and Ca4.94(2)Sm0.06Al2Sb6 were indeed novel n‐type Zintl phase semiconductors with the maximum electrical conductivities of 69.51 and 75.51 S/cm at 846 K and the Seebeck coefficients of −43.26 and − 29.00 μV/K at 703 K, respectively. Density functional theory calculations proved that the successful n‐type doping should be attributed to a small margin of slight antibonding states near EF on the Sb1Sb1 crystal orbital Hamilton population (COHP) curve.