Impurity phase elimination enabled high thermoelectric and mechanical performance in GeTe alloyed with AgSbSe2

Alloying IV-VI group materials with ternary chalcogenides (ABX 2 , A = Ag, Cu, Na; B = Sb, Bi; X = Te, Se, S) has been employed as an effective strategy for optimizing thermoelectric performance. Yet, on one hand, when using ABX 2 alloying, the emergence of the second phase is extremely likely, which may lead to material instability at high temperatures. On the other hand, research on the mechanical properties of these solid solutions is lacking, which is crucial for practical applications of thermoelectric device. In this work, taking alloying GeTe with AgSbSe 2 as a case study, the Ag-rich second phase is successfully eliminated by precisely regulating the Ag/Sb ratio. More importantly, we found that the mechanical properties of Ag-rich free (GeTe) 80 (Ag 0.8 Sb 1.2 Se 2 ) 20 are better than that of Ag-rich (GeTe) 80 (AgSbSe 2 ) 20 , and the Vickers hardness, compressive strength and fracture toughness increase from 230 HV, 105 MPa, and 1.49 MPa m 1/2 for (GeTe) 80 (AgSbSe 2 ) 20 to 250 HV, 166 MPa, and 1.75 MPa m 1/2 for (GeTe) 80 (Ag 0.8 Sb 1.2 Se 2 ) 20 . Furthermore, nanoindentation results demonstrate that the deterioration of mechanical properties in (GeTe) 80 (AgSbSe 2 ) 20 originates from Ag-rich second phases. Moreover, due to the introduced band convergence and significant mass and strain fluctuations by Ag and Sb substituting Ge and Se substituting Te, the thermoelectric performance is enhanced over the measured temperature range, and an average ZT ave of 1.07 within 300 - 773 K in (GeTe) 80 (Ag 0.8 Sb 1.2 Se 2 ) 20 is achieved. Our work highlights the importance of the absence of second phases in enhancing mechanical properties in alloying IV-VI group materials with ternary chalcogenides.