The Solid Solution Series (GeTe)x(LiSbTe2)2 (1 ≤ x ≤ 11) and the Thermoelectric Properties of (GeTe)11(LiSbTe2)2

Exchanging one Ge2+ with two Li+ per formula unit in (GeTe)(n)(Sb2Te3) (n = 1, 2, 3, ...) eliminates cation vacancies, because it leads to an equal number of cations and anions. This substitution results in the solid solution (GeTe)(x)(LiSbTe2)(2) (with x = n - 1, but n not necessarily an integer). For x < 6, these stable compounds crystallize in a rock-salt-type structure with random cation disorder. Neutron data show that a small fraction of Ge occupies tetrahedral voids for x = 2 and 3. For x> 6, (GeTe)(x)(LiSbTe2)(2) forms a GeTe-type structure that shows a phase transition to a cubic high-temperature phase at ca. 280 degrees C. The thermoelectric properties of (GeTe)(11)(LiSbTe2)(2) have been investigated and show that this compound is a promising thermoelectric material with a ZT value of 1.0 at 450 degrees C. The high ZT value of the thermodynamically stable compound is caused by a low phononic contribution to the thermal conductivity; probably, Li acts as a "pseudo-vacancy".