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Rare earth metal-doped Zintl phase thermoelectric materials:The Yb5xRExAl2Sb6(RE=Pr, Nd, Sm) system
Yeongjin Hong,Tae-Soo You,Seongbeom Yeon,Jiwon Jeong,Dohyun Moon 대한화학회 2022 Bulletin of the Korean Chemical Society Vol.43 No.10
Three Zintl phase solid solutions in the Yb5xRExAl2Sb6(RE=Pr, Nd, Sm)system have successfully been synthesized by arc melting followed by anneal-ing. The isotypic crystal structure of these compounds was characterized byPXRD and SXRD analyses, and their Ca5Al2Bi6-type structure (space groupPbam,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 frame-works were originally built from the two neighboring tetrahedral [AlSb4] moie-ties via the Sb1-Sb1 bridges. The site-preference of RE3+for the Yb3/RE-sitewith the mixed occupation ratio between ca. 9% and 16% of RE3+was eluci-dated by the size-factor criterion based on the size match between the cationicsize and the site volume. The band structures, density of states, and crystalorbital 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 peaksnear the Fermi level resulting in the improved Seebeck coefficients. The electri-cal transport property measurements proved that despite the successful addi-tion ofn-type RE3+dopants in the title Yb5xRExAl2Sb6system, the electricalconductivity decreased due to the canceling off of the newly addedn-type car-riers by the already existingp-type carriers resulting in still thep-type character.However, the enhanced Seebeck coefficients predicted by the increased effec-tive mass from the DFT calculations eventually improved the overall power fac-tor of the RE3+-doped title compounds.