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 °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 °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”.