Medium Entropy‐Enabled High Performance Cubic GeTe Thermoelectrics

Abstract

The configurational entropy is an emerging descriptor in the functional materials genome. In thermoelectric materials, the configurational entropy helps tune the delicate trade‐off between carrier mobility and lattice thermal conductivity, as well as the structural phase transition, if any. Taking GeTe as an example, low‐entropy GeTe generally have high carrier mobility and distinguished zT > 2, but the rhombohedral‐cubic phase transition restricts the applications. In contrast, despite cubic structure and ultralow lattice thermal conductivity, the degraded carrier mobility leads to a low zT in high‐entropy GeTe. Herein, medium‐entropy alloying is implemented to suppress the phase transition and achieve the cubic GeTe with ultralow lattice thermal conductivity yet decent carrier mobility. In addition, co‐alloying of (Mn, Pb, Sb, Cd) facilitates multivalence bands convergence and band flattening, thereby yielding good Seebeck coefficients and compensating for decreased carrier mobility. For the first time, a state‐of‐the‐art zT of 2.1 at 873 K and average zTave of 1.3 between 300 and 873 K are attained in cubic phased Ge0.63Mn0.15Pb0.1Sb0.06Cd0.06Te. Moreover, a record‐high Vickers hardness of 270 is attained. These results not only promote GeTe materials for practical applications, but also present a breakthrough in the burgeoning field of entropy engineering.

(GeTe)1–x(AgSnSe2)x: Strong Atomic Disorder-Induced High Thermoelectric Performance near the Ioffe–Regel Limit

“…Interestingly, all elements are homogeneously distributed in the GeTe matrix after further Sb alloying (Figure S3, Supporting Information), demonstrating the gradual dissolution of Ge, Ag-rich, and Se-rich precipitates in our high-entropy Ge 0.8– y Sb y Te 0.8 (AgSnSe 2 ) 0.2 series. The precipitates to be dissolved into the matrix, as well as the resultant cationic and anionic site disorders in light of the random distribution of all elements, may be ascribed to the high entropy effect, which is similar to the previous results. , …”

“…It is proverbial that GeTe is intrinsically off-stoichiometric with Ge vacancies and Ge-precipitations . According to the result of the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), we found that Ag-rich and Se-rich second phases coexist in the AgSnSe 2 alloying sample (Figure S2, Supporting Information).…”

“…Doping or alloying yields atomic disorder, and the level of such disorder can be quantified approximately according to the configurational entropy Δ S = – R ∑ i = 1 n x i ln x i , where n is the number of alloying components, x i is the mole fractions of the i th component, and R is the gas constant. , Thermodynamically, increasing atomic disorder and hence Δ S is an effective strategy to stabilize the thermoelectric favorable cubic structure. − Apparently, the Δ S significantly increases from 0 R for GeTe to 1.5 R for (GeTe) 0.8 (AgSnSe 2 ) 0.2 and then to 1.92 R for Ge 0.55 Sb 0.25 Te 0.8 (AgSnSe 2 ) 0.2 , reaching the high entropy region with Δ S > 1.5 R (Figure a). As shown in Figure b, the room-temperature powder X-ray diffraction patterns of pristine GeTe can be exclusively indexed to the rhombohedral phase.…”

“…Specially, the high α values over the whole temperature range (157–216 μVK –1 ) are attained for Ge 0.55 Sb 0.25 Te 0.8 (AgSnSe 2 ) 0.2 . In addition to n H , α is also related to m * . Hence, we calculated the Pisarenko plot according to the single parabolic band (SPB) model to investigate the influence of AgSnSe 2 and Sb co-alloying on m * and the result is plotted in Figure c.…”

Phase Modulation Enabled High Thermoelectric Performance in Polycrystalline GeSe0.75Te0.25

“…IV-VI compounds such as PbTe, [1][2][3][4] SnSe, [5][6][7][8][9] and GeTe, [10][11][12][13][14][15] are exceptional TE materials with zT ≥2 and very promi sing in practical application. [16] Although these compounds crystalize in different structures at room temperature, namely cubic, orthorhombic and rhombohedral structures for PbTe, SnSe, and GeTe, respectively, they still can be regarded as derivatives originating from the NaCl structure, where cations and anions are separated from each other.…”