Cahana Meital, Hayun Hagay, Gelbstein Yaniv
The Unit of Energy Engineering, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
Nuclear Research Center of the Negev, P.O.B. 9001 Beer-Sheva 84190, Israel.
Phys Chem Chem Phys. 2022 Sep 14;24(35):21223-21232. doi: 10.1039/d2cp02926j.
Phase separation by the spinodal decomposition or nucleation and growth mechanisms is an established method for the generation of thermodynamically stable sub-micron features, capable of both reducing the lattice thermal conductivity, , and stabilizing its value, while obtaining high and stable thermoelectric (TE) figure of merit values during practical applications. In the Mg(Si,Sn,Ge) class of TE materials, a miscibility gap and a thermodynamic tendency of phase separation were reported in the MgSi-MgSn quasi-binary section of the ternary phase diagram, capable of enhancing and stabilizing the TE performance, by minimization. Yet, no such tendency was ever reported for the MgSi-MgGe quasi-binary system, prohibiting the fulfillment of its TE potential. It is currently shown that a similar (yet, less pronounced) tendency of phase separation is also apparent in the MgSi-MgGe quasi-binary system, into MgSi- and MgGe-rich MgSiGe phases. This phenomenon is enhanced upon bismuth doping. Upon 1.5, 2, and 2.5% bismuth doping of MgSiGe, following induction melting and hot-pressing, the solubility limit of Bi was found as 1.5-2%, while increasing the bismuth content resulted in significant MgBi segregation into grain boundaries. The combined phase separation and segregation effects on reduction with the electronic effect of Bi doping resulted in a reasonably high maximal of 0.9, which was observed upon 2.5% Bi doping.
通过旋节线分解或成核与生长机制进行相分离是一种既定的方法，用于生成热力学稳定的亚微米特征，既能降低晶格热导率，又能稳定其值，同时在实际应用中获得高且稳定的热电（TE）优值。在Mg(Si,Sn,Ge)类TE材料中，在三元相图的MgSi-MgSn准二元截面中报道了混溶间隙和相分离的热力学趋势，通过最小化能够增强和稳定TE性能。然而，对于MgSi-MgGe准二元体系，从未报道过这种趋势，这阻碍了其TE潜力的实现。目前表明，在MgSi-MgGe准二元体系中也存在类似（但不太明显）的相分离趋势，形成富含MgSi和MgGe的MgSiGe相。铋掺杂会增强这种现象。在对MgSiGe进行1.5%、2%和2.5%的铋掺杂后，经过感应熔炼和热压，发现Bi的溶解度极限为1.5 - 2%，而铋含量的增加导致大量MgBi偏析到晶界。相分离和偏析对降低晶格热导率的综合影响与铋掺杂的电子效应导致了在2.5%铋掺杂时观察到的高达0.9的合理最大热电优值。
