2012/01/11 by Andrew F. May, A. F. May, M. A. McGuire +13 · 94 citations
Chemistry · Materials Science · Physics and Astronomy · #Advanced Thermoelectric Materials and Devices #Analytical Chemistry (journal) #Chemistry #Condensed matter physics #Crystallography #Electrical resistivity and conductivity #Heusler alloys: electronic and magnetic properties #Materials science #Physics #Rare-earth and actinide compounds #Seebeck coefficient #Thermodynamics #Thermoelectric effect #cond-mat.mtrl-sci #cond-mat.other
paper · pdf · doi:10.1103/physrevb.85.035202
published in Physical Review B 85(3) (American Physical Society)
openalex publication_date 2012/01/11 · arxiv created 2012/01/12 · arxiv updated 2012/01/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The thermoelectric transport properties of CaMg2Bi2, EuMg2Bi2, and YbMg2Bi2 were characterized between 2 and 650 K. As synthesized, the polycrystalline samples are found to have lower p-type carrier concentrations than single-crystalline samples of the same empirical formula. These low carrier concentration samples possess the highest mobilities yet reported for materials with the CaAl2Si2 structure type, with a mobility of \ensuremath∼740 cm2/V/s observed in EuMg2Bi2 at 50 K. Despite decreases in the Seebeck coefficient (\ensuremathα) and electrical resistivity (\ensuremathρ) with increasing temperature, the power factor (\ensuremathα2\ensuremathρ) increases for all temperatures examined. This behavior suggests a strong asymmetry in the conduction of electrons and holes. The highest figure of merit (zT) is observed in YbMg2Bi2, with zT approaching 0.4 at 600 K for two samples with carrier densities of approximately 2\ifmmode×\else\texttimes\fi1018 cm^\ensuremath-3 and 8\ifmmode×\else\texttimes\fi1018 cm^\ensuremath-3 at room temperature. Refinements of neutron powder diffraction data yield similar behavior for the structures of CaMg2Bi2 and YbMg2Bi2, with smooth lattice expansion and relative expansion in c being \ensuremath∼35% larger than relative expansion in a at 973 K. First-principles calculations reveal an increasing band gap as Bi is replaced by Sb and then As, and subsequent Boltzmann transport calculations predict an increase in \ensuremathα for a given n associated with an increased effective mass as the gap opens. The magnitude and temperature dependence of \ensuremathα suggests higher zT is likely to be achieved at larger carrier concentrations, roughly an order of magnitude higher than those in the current polycrystalline samples, which is also expected from the detailed calculations.