Enhancement of the Thermal Stability and Thermoelectric Properties of Yb₁₄MnSb₁₁ by Ce Substitution

Abstract

Yb14MnSb11 is a p-type high-temperature thermoelectric material with operational temperatures as high as 1273 K. Rare-earth (RE) substitution into this phase has been shown to increase the melting point further while also decreasing the sublimation rate. Solid solutions of 3+ RE elements with Yb2+ in Yb14MnSb11 have shown to have increased stability against oxidation. Ce is an abundant RE element, and the substitution of Ce3+ on the Yb2+ sites should increase the thermoelectric efficiency of the material due to a decrease in carrier concentration. Samples of Yb14–x Ce x MnSb11 (x ∼ 0.4) were synthesized using ball milling, followed by annealing and consolidation via spark plasma sintering. The systematic addition of a small increase of excess Mn and the resulting compositions were investigated. Small amounts of impurities in the samples, such as Yb2O3 and Mn, are correlated with negative attributes in the resistivity data. Hall effect measurements revealed a reduced carrier concentration of ∼44% at 600 K over Yb14MnSb11, and adjusting the stoichiometry toward Yb13.6Ce0.4MnSb11 leads to increases in resistivity and the Seebeck coefficient with a reduction in thermal conductivity. Yb13.6Ce0.4MnSb11 shows an improved average zT avg = 0.80 when compared to Yb14MnSb11 (0.71) and no degradation when exposed to ambient air for 77 days at room temperature. Thermogravimetric analysis of air oxidation shows that Yb13.6Ce0.4MnSb11 and Yb14MnSb11 do not oxidize until 700 K.

Complex Structural Disorder in the Zintl Phases Yb10MnSb9 and Yb21Mn4Sb18

“…These two phases will be difficult to analyze by other common analytical techniques such as microprobe analysis, especially in situations when unpolished samples are examined and proper calibration standards are unavailable. A casual survey of the literature revealed multiple works that dealt with the formation of the “Yb 11 Sb 10 ” phase, in the preparation and optimization of Yb 14 MnSb 11 samples for thermoelectric studies. − According to these reports, “Yb 11 Sb 10 ” was produced even with an excess of Mn, which appears to contradict the in-depth synthetic work carried out by us and described in this paper. Given the above, it is not unreasonable to expect that some of the literature may have mistakenly confused the Yb 10 MnSb 9 and Yb 11 Sb 10 phases.…”

Ultralow Thermal Conductivity and High Thermopower in a New Family of Zintl Antimonides Ca10MSb9 (M = Ga, In, Mn, Zn) with Complex Structures and Heavy Disorder

“…Since the crystals grow under constantly changing conditions (temperature, composition of the melt), different crystals from the same reaction or even different parts of a crystal may have inherent inhomogeneities, which result in irreproducible transport data. However, the absolute values of ρ­( T ) at room temperature for those crystals were always on the order of 1 Ω·cm, which is about 2–3 orders of magnitude higher than the corresponding values in benchmark thermoelectric materials, such as PbTe, Yb 14 MnSb 11 , and their derivatives. ,,, …”

“…However, the absolute values of ρ(T) at room temperature for those crystals were always on the order of 1 Ω•cm, which is about 2−3 orders of magnitude higher than the corresponding values in benchmark thermoelectric materials, such as PbTe, Yb 14 MnSb 11 , and their derivatives. 12,13,114,115 3.5. Magnetization.…”

p-Type to n-Type Conversion through the “Bypass” Phase Transition in the Zintl-Phase Thermoelectric Materials

“…Finding a sustainable clean energy source is an enduring issue for humankind in modern society. Despite our continuous efforts to discover and develop various energy sources, we easily overlook the fact that about 67% of the energy we use is wasted in the form of heat. , Since thermoelectric (TE) materials can directly convert wasted heat sources into electricity, these materials and devices adapting TE materials have been considered as one of the smartest solutions for energy-recycling purposes. − Among the numerous candidates for this TE application, the Zintl phase is considered an excellent candidate with respect to its intrinsically semiconducting property and complex crystal structure, both of which are required for good TE candidates. − In particular, the Zintl-phase A 5 M 2 Pn 6 (A = Ca, Sr, Eu, and Yb; M = Al, Ga, and In; Pn = As, Sb, and Bi) series has been extensively investigated by worldwide researchers for TE applications. − Our recent studies for the Zintl-phase Ca 5– x Yb x Al 2 Sb 6 (1.0 ≤ x ≤ 5.0) system revealed that some Yb-rich compounds having a particular range of composition initially adopted the Ca 5 Al 2 Bi 6 -type phase, but they underwent a phase transition to the Ca 5 Ga 2 As 6 -type phase through the annealing process . Moreover, their electrical transport properties were also shifted from metallic to semiconducting during this phase transition.…”