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Abstract:
Zintl compounds with chemical formula Yb5M2Sb6 (M = Al, Ga, and In) form
one of two known A(5)M(2)Pn(6) structure types characterized by double
chains of corner-linked MPn(4) tetrahedra bridged by Pn(2) dumb-bells.
High temperature electronic and thermal transport measurements were used
to characterize the thermoelectric properties of Yb5M2Sb6 compounds. All
samples were found to exhibit similar high p-type carrier
concentrations, low resistivity and low Seebeck coefficients in
agreement with the band structure calculations. These results, combined
with previous studies, suggest that Yb5M2Sb6 compounds are semi-metals
(i.e., they lack an energy gap between the valence and conduction
bands), in contrast to the semi-conducting alkaline earth (Ca, Sr, Ba)
and Eu based A(5)M(2)Sb(6) compounds. Yb5M2Sb6 compounds have very low
lattice thermal conductivity, comparable to other closely related
A(5)M(2)Sb(6) and A(3)MSb(3) phases. However, due to the semimetallic
behaviour, the figure of merit of investigated samples remains low (zT <
0.15).
