Rare earth metal‐doped Zintl phase thermoelectric materials: The Yb5−xRExAl2Sb6 (RE=Pr, Nd, Sm) system

Abstract

AbstractThree Zintl phase solid solutions in the Yb5 − xRExAl2Sb6 (RE = Pr, Nd, Sm) system have successfully been synthesized by arc melting followed by annealing. The isotypic crystal structure of these compounds was characterized by PXRD and SXRD analyses, and their Ca5Al2Bi6‐type structure (space group Pbam, Z = 2) was described as a combination of (1) the 3‐dimensional anionic [Al2(Sb4Sb4/2)] frameworks and (2) the space‐filling cations Yb2+ and RE3+ located in between the anionic frameworks. In particular, the anionic frameworks were originally built from the two neighboring tetrahedral [AlSb4] moieties via the Sb1‐Sb1 bridges. The site‐preference of RE3+ for the Yb3/RE‐site with the mixed occupation ratio between ca. 9% and 16% of RE3+ was elucidated by the size‐factor criterion based on the size match between the cationic size and the site volume. The band structures, density of states, and crystal orbital Hamilton population curve analyses were conducted by the tight‐binding linear muffin‐tin orbital method, and the results proved that the RE3+‐doping increased the band degeneracies and the number of resonance peaks near the Fermi level resulting in the improved Seebeck coefficients. The electrical transport property measurements proved that despite the successful addition of n‐type RE3+ dopants in the title Yb5 − xRExAl2Sb6 system, the electrical conductivity decreased due to the canceling off of the newly added n‐type carriers by the already existing p‐type carriers resulting in still the p‐type character. However, the enhanced Seebeck coefficients predicted by the increased effective mass from the DFT calculations eventually improved the overall power factor of the RE3+‐doped title compounds.