High-performance n-type YbxCo4Sb12: from partially filled skutterudites towards composite thermoelectrics

Abstract

The filling fraction limit (FFL) of skutterudites, that is, the complex balance of formation enthalpies among different species, is an intricate but crucial parameter for achieving high thermoelectric performance. In this work, we synthesized a series of Yb x Co 4 Sb 12 samples with x = 0.2-0.6 and systemically studied the FFL of Yb, which is still debated even though this system has been extensively investigated for decades. Our combined experimental efforts of X-ray diffraction, microstructural and quantitative compositional analyses clearly reveal a Yb FFL of~0.29 in CoSb 3 , which is consistent with previous theoretical calculations. The excess Yb in samples with x40.35 mainly form metallic YbSb 2 precipitates, significantly raising the Fermi level and thus increasing the electrical conductivity and decreasing the Seebeck coefficient. This result is further corroborated by the numerical calculations based on the Bergman's composite theory, which accurately reproduces the transport properties of the x40.35 samples based on nominal Yb 0.35 Co 4 Sb 12 and YbSb 2 composites. A maximum ZT of 1.5 at 850 K is achieved for Yb 0.3 Co 4 Sb 12 , which is the highest value for a single-element-filled CoSb 3 . The high ZT originates from the high-power factor (in excess of 50 μW cm-K − 2 ) and low lattice thermal conductivity (well below 1.0 W m-K − 1 ). More importantly, the large average ZTs, for example,~1.05 for 300-850 K and~1.27 for 500-850 K, are comparable to the best values for n-type skutterudites. The high thermoelectric and thermomechanical performances and the relatively low air and moisture sensitivities of Yb make Yb-filled CoSb 3 , a promising candidate for large-scale power generation applications.

Resonant level-induced high thermoelectric response in indium-doped GeTe

“…[1][2][3] The lattice thermal conductivity κ L can typically be reduced via a low sound velocity, 4 a large lattice anharmonicity, [5][6][7][8] rattling atoms in lattice voids, [9][10][11] or even liquid-like sublattices, [12][13][14][15] and multi-scale microstructures. [16][17][18][19][20] The electronic properties can be improved by band convergence, [21][22][23][24][25][26] dimensionality reduction, 1,27-29 and resonant levels. 2,30 By modulating the electronic and thermal terms, the figure of merit and energy conversion efficiency of thermoelectric materials can be optimized for widespread applications.…”

Effects of partial La filling and Sb vacancy defects on CoSb3 skutterudites

“…5 La is a unique filler atom to study in the sense that it is the lightest lanthanide element and the only one without f-electrons compared with other studied rare earth filler atoms such as Ce [34,35], Pr [36], Eu [37], and Yb [38,39,40]. The studies on La filling may shed light on the role of f-electrons in filling and rattling when compared with studies on other elements.…”

Термоэлектрические свойства скуттерудитов Ce-=SUB=-x-=/SUB=-Nd-=SUB=-y-=/SUB=-Co-=SUB=-4-=/SUB=-Sb-=SUB=-12-=/SUB=-

“…Октапоры могут быть заполнены тяжелыми элементами -раттлерами, которые ведут себя как независимые осцилляторы, взаимодействие которых с фононными модами кристаллической решетки приводит к существенному уменьшению фононного вклада в об-щую теплопроводность скуттерудитов. Большое количе-ство научных работ посвященo улучшению термоэлек-трических свойств скуттерудитов за счет добавления в кристаллические пустоты таких элементов как Ce, Ba, Yb и La [10][11][12][13][14][15]. Поскольку было отмечено, что наи-большего рассеяния фононов удается достигнуть, если раттлеры будут иметь разные массы и, как следствие, разные частоты колебаний, ряд работ был посвящен исследованию термоэлектрических свойств заполненных скуттерудитов, где в качестве раттлеров выступала ком-бинация редкоземельных материалов, таких как Сe−La и La−Yb−Ba [16,17].…”