Phase diagram of In–Co–Sb system and thermoelectric properties of In-containing skutterudites

Abstract

In-containing skutterudites have long attracted much attention and debate partly due to the solubility limit issue of indium in CoSb 3 . The isothermal section of the equilibrium phase diagram for the In-Co-Sb system at 873 K is proposed using knowledge of the related binary phase diagrams and experimental data, which explains the debated indium solubility that depends on Sb content. In this paper, a series of In-containing skutterudite samples (In x Co 4 Sb 12Àx/3 with x varying from 0.075 to 0.6 and In 0.3 Co 4Ày Sb 11.9+y with y changing from À0.20 to 0.20) are synthesized and characterized. X-ray analysis and scanning electron microscopy images indicate that, up to x ¼ 0.27, single-phase skutterudites are obtained with lattice constant increasing with In fraction x. A fixed-composition skutterudite In 0.27AE0.01 Co 4 Sb 11.9 was determined for the Co-rich side of In-CoSb 3 which is in coexistence with liquid InSb and CoSb 2 . Indium, like Ga, is expected, from DFT calculations, to form compound defects in In-containing skutterudites. However, relatively higher carrier concentrations of In-containing skutterudites compared to Ga-containing skutterudites indicate the existence of not fully charge-compensated compound defects, which can also be explained by DFT calculations. The net n-type carrier concentration that naturally forms from the complex defects is close to the optimum for thermoelectric performance, enabling a maximum zT of 1.2 for the fixed skutterudite composition In 0.27 Co 4 Sb 11.9 at 750 K. Broader contextIn-containing skutterudites have long attracted much attention due to the high thermoelectric efficiency and proposed application in automotive waste heat recovery. However there has been much debate over how much indium is actually soluble in CoSb 3 or whether it simply precipitates out as nanoparticles. In this study, we provide both theoretical and experimental evidence for the presence of compound defects in skutterudites with indium impurities. The isothermal section of ternary phase diagram of In-Co-Sb system at 873 K is proposed, which naturally explains the solubility debate and the confusion concerning the various reports of maximum solubility of indium in the skutterudite phase. The phase relations allow us to identify a stable skutterudite composition In 0.27 Co 4 Sb 11.9 with high zT values greater than 1. A wide range of nominal compositions will produce the same skutterudite material as the majority phase which will enable the exibility needed to produce commercial quantities of reliable, uniform quality.

Defect-Controlled Electronic Structure and Phase Stability in Thermoelectric Skutterudite CoSb3

“…into the lattice cages of the CoSb 3 structure to remarkably reduce the κ thermal conductivity. [10][11][12][13][14][15][16] For example, Shi et al proposed a simple electronegativity rule to determine whether a skutterudite phase with guest atoms can stably form. 16 The filling fraction limit (FFLs) of guest atoms was predicted in CoSb 3 by considering not only the interaction between the guest and host atoms but also the formation of secondary phases.…”

Influence of Nanopores on the Tensile/Compressive Mechanical Behavior of Crystalline CoSb3: A Molecular Dynamics Study

“…Skutterudite CoSb 3 thermoelectric material has been recognized as one of the most potential highperforming material in the medium temperature range. [5][6][7] Compared with other thermoelectric materials, the thermal conductivity of skutterudite CoSb 3 k is relatively a little too high. The CoSb 3 research focuses on how to decrease the thermal conductivity.…”

Thermoelectric Properties of In<i>_x</i>FeCo₃Sb₁₂ Consisting Mainly of In-Filled <i>p</i>-Type Skutterudites

“…[15][16][17] Among the ller candidates, we selected In as an appropriate ller element, because group 13 elements were reported to cause excellent TE properties for n-type lled skutterudites. [18][19][20][21] In deed, an indium (In) lled CoSb 3 exhibits the highest zT exceeding unity. 18) Besides, the positive sign of Seebeck coef cient was reported for In-lled (Co,Fe)Sb 3 by several different groups.…”

“…[18][19][20][21] In deed, an indium (In) lled CoSb 3 exhibits the highest zT exceeding unity. 18) Besides, the positive sign of Seebeck coef cient was reported for In-lled (Co,Fe)Sb 3 by several different groups. Leszczynski et 4 Sb 12 (y > 1/3), these impurity phases lead to the reduction of Seebeck coefcient.…”