Kumar Anil, Vermeulen Paul A, Kooi Bart J, Rao Jiancun, Schwarzmüller Stefan, Oeckler Oliver, Blake Graeme R
Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4, 9747 AG Groningen The Netherlands
AIM Lab, Maryland NanoCenter, University of Maryland, College Park Maryland 20742 USA.
RSC Adv. 2018 Dec 19;8(74):42322-42328. doi: 10.1039/c8ra05768k.
The alloy (GeTe)(AgSbTe), commonly known as TAGS-85, is one of the best performing p-type thermoelectric materials in the temperature range 200-500 °C. In all reports thus far, TAGS-85 adopts a rhombohedral crystal structure at room temperature and undergoes a reversible transition to a cubic phase in the middle of the operating temperature range. Here, we report on a novel, metrically cubic polymorph of TAGS-85 that can be obtained at room temperature using a particular cooling protocol during initial synthesis. This polymorph transforms irreversibly on initial heating to a 21-layer trigonal structure containing ordered cation vacancy layers, driven by the spontaneous precipitation of argyrodite-type AgGeTe. We show that the precipitation of AgGeTe is detrimental to the thermoelectric performance of TAGS-85 due to an increase in the vacancy concentration, which makes the samples more metallic in character and significantly reduces the Seebeck coefficient. The precipitation of AgGeTe can be suppressed by careful control of the synthesis conditions.
合金(GeTe)(AgSbTe)，通常称为TAGS - 85，是200 - 500°C温度范围内性能最佳的p型热电材料之一。在迄今为止的所有报告中，TAGS - 85在室温下采用菱面体晶体结构，并在工作温度范围中间经历向立方相的可逆转变。在此，我们报告一种新型的、在初始合成过程中使用特定冷却方案可在室温下获得的TAGS - 85的立方多晶型体。这种多晶型体在初次加热时不可逆地转变为包含有序阳离子空位层的21层三角结构，这是由硫银锗矿型AgGeTe的自发沉淀驱动的。我们表明，由于空位浓度增加，AgGeTe的沉淀对TAGS - 85的热电性能有害，这使样品具有更多金属特性并显著降低塞贝克系数。通过仔细控制合成条件可以抑制AgGeTe的沉淀。
