Effect of Cu Substitution on Thermoelectric Properties of Ge Clathrates

Abstract

We have prepared polycrystalline n-type Ba 8 Cu x Ga y Ge 46ÀxÀy (x ¼ 0{5, y ¼ 16 À 3x) clathrate compounds by arc melting and spark plasma sintering techniques and investigated the effect of Cu substitution for Ge on their thermoelectric properties. The Hall carrier concentration for Cu-substituted compounds is almost constant at the order of 10 20 cm À3 , which is comparable to that for Ba 8 Ga 16 Ge 30 stoichiometric compounds. The Seebeck coefficient for these compounds is comparable to that for n-Ba 8 Ga y Ge 46Ày compounds. From the analysis of the properties, the effective mass of the conduction band is estimated to be about 1.4 m 0 , which is equivalent to or slightly smaller than that of n-Ba 8 Ga y Ge 46Ày compounds. The Hall mobility increases as the Cu composition increases. Its temperature dependence obeys approximately T À1=2 dependence in the range of 80-300 K, indicating the dominance of the alloy disorder scattering. Two models are discussed to account for the reduction in the alloy disorder scattering by Cu substitution.

Theoretical and Experimental Study on Thermoelectric Properties of Ba8TM x Ga y Ge46–x–y (TM = Zn, Cu, Ag) Type I Clathrates

“…The discrepancy between the nominal composition and the electronic properties is a known issue in Ge clathrates. 31 In the case of Ni-containing clathrate, Johnsen et al 30 suggested formation of vacancies as a possible explanation for this disagreement, and this seems to be a reasonable explanation for the variations observed in our samples as well.…”

Crystal structure and thermoelectric properties of KxBa8−xZnyGe46−y clathrates

“…8,11,13,14 The weighted mobilities of the K x Ba 8Àx Zn y Ge 46Ày samples were not as large as those of the related clathrates, but the K 8 Zn 4 Ge 42 sample showed a relatively large value as a result of its larger effective mass. To sum up so far, we could not obtain increases in mobility and in weighted mobility for K x Ba 8Àx Zn y Ge 46Ày , including K 4 Ba 4 Zn 6 Ge 40 with a highly ordered framework.…”

“…1). [18][19][20][21][22][23][24][25][26] 13 where the observed increases in mobility were mainly as a result of a decrease in the number of substituting atoms. Johnsen et al characterized several Ba 8 Ni 6Àx Ge 40þx (0 x 0.6) samples.…”

“…223, Pm 3n) have been reported to possess ZT values of approximately 1 at elevated temperatures; 2,3,[7][8][9] the maximum ZT values of singlecrystal and polycrystalline samples are 1.35 at 900 K for Ba 8 Ga 16 Ge 30 (Ref. 7) and 1.2 at 1000 K for Ba 8 Ni 0.31 Zn 0.52 Ga 13.06 Ge 32.2 (Ref. 8).…”

First-Principles Study of Electronic Structure and Thermoelectric Properties for Guest Substituted Clathrate Compounds Ba<SUB>6</SUB>R<SUB>2</SUB>Au<SUB>6</SUB>Ge<SUB>40</SUB> (R=Eu or Yb)

“…[4][5][6][7][8][9][10][11][12][13] Anno et al 4,5,7,8) systematically investigated the thermoelectric properties of Ge clathrate compounds containing the transition elements (Cu, Ag, Au, Pd, Pt) in host. They have found that the Seebeck coefficient is enhanced due to the increased effective mass by Ag, Au, Pd, and Pt substitution.…”