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

Abstract

Exchanging one Ge(2+) 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".

Increasing Seebeck Coefficients and Thermoelectric Performance of Sn/Sb/Te and Ge/Sb/Te Materials by Cd Doping

“…As a consequence, stable modifi cations with decreased σ and almost unchanged S are obtained; they reach ZT values of up to 1.0 at 450 °C for Li 2 Ge 11 Sb 2 Te 15 . [ 14 ] Li atoms probably act as pseudovacancies as corroborated by values of κ p similar to those of vacancy-containing GST materials. Isovalent cation substitution, e.g., the partial replacement of Sb 3+ by In 3+ , yields solid solutions like Ge 12 (Sb 1x In x ) 2 Te 15 (0 ≤ x ≤ 1) with increased ZT values for T ≤ 200 °C compared to the unsubstituted GST compounds.…”

Thermoelectric Enhancement of Different Kinds of Metal Chalcogenides

“…[105][106] Another big issue for utilizing GeTe based materials lies in their narrow optimum operating temperature, ranging from 680 K to 780 K, because a phase transition between the rhombohedral lattice (R3m) and the cubic phase (Fm-3m) occurs at about 700 K. The instability of the cubic phase is probably due to their high concentration of vacancies, which involves "incomplete" coordination spheres and a large energy gain when ordered structures are formed. [107] precipitates was achieved with good reproducibility. [108] The pseudo-binary PbTe-GeTe phase diagram shows unlimited mutual solubility of its end members in both liquid and solid states at high temperature, but phase separation driven by spinodal decomposition (miscibility gap) exists below 860 K. [103,109] …”

Realizing a stable high thermoelectric zT ∼ 2 over a broad temperature range in Ge1−x−yGaxSbyTe via band engineering and hybrid flash-SPS processing

“…Some of the strategies for GeTe based materials to enhance the power factor and/or to suppress latt have been adopted on compositions such as GeTe-AgSbTe2 (TAGS), 31 GeTe-LiSbTe2, 32 GeTe-AgInTe2, 33 GeTe-AgSbSe2, 34 (GeTe)nSb2Te3, 35 Ge1-xPbxTe, 36 Ge1-xBixTe, 37 (Bi2Te3)nGe1-xPbxTe, 38 Ge1-xInxTe, 39 GeTe1-xSe, 40 Ge1-…”