Improved Power Factor and Mechanical Properties of Composites of Yb₁₄MgSb₁₁ with Iron

Abstract

Composite phases have been shown to improve both the thermoelectric efficiency and mechanical properties of materials. Here, we demonstrate an improved thermoelectric figure of merit, power factor, and mechanical properties for the high-temperature p-type Zintl phase Yb 14 MgSb 11 . Composites with 0, 1, 2, 3, 4, 6, and 8 vol % 6−10 μm reduced Fe powder were prepared via a fast, scalable, mechanical milling and spark plasma sintering procedure. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that Fe is not incorporated into the Yb 14 MgSb 11 structure. First-order reversal curves and scanning electron microscopy images show that the Fe inclusions are larger and closer together with increasing Fe content. Thermogravimetric and differential scanning calorimetry show that the composites are stable up to 1273 K. The elastic constants of the 8 vol % Fe composite were measured by resonant ultrasound spectroscopy and show that Yb 14 MgSb 11 becomes stiffer with increasing Fe volume % and SEM after indentations show crack arresting occurs at the Fe interface. Thermoelectric properties on dense pellets are measured from 300 K − 1273 K. The thermoelectric power factor (PF = S 2 /ρ) increases with increasing Fe content, with the 8 vol % Fe resulting in 40% higher PF than pristine Yb 14 MgSb 11 . The increase in PF is attributed to a systematic reduction in electrical resistivity. Peak thermoelectric figure of merit [zT = (S 2 T)/(κρ)] is observed at 3 vol % Fe, an 11% improvement in zT compared to Yb 14 MgSb 11 . Yb 14 MgSb 11 composites with Fe are compatible with Ce 0.9 Fe 3.5 Co 0.5 Sb 12 for thermoelectric generator couple segmentation. KEYWORDS: composite, thermoelectric, transport properties, Zintl phase, SPS synthesis, first-order reversal curves PFS 2 =ρ by band structure engineering, such as band convergence, tuning the electronic states with resonance levels, or simple substitutional alloying. There has also been significant research

Discovery of multivalley Fermi surface responsible for the high thermoelectric performance in Yb 14 MnSb 11 and Yb 14 MgSb 11

“…Synthesis was adapted from the literature ( 30 ). Ten grams of stoichiometric Mg and Sb was placed in a SPEX tungsten carbide grinding vial set (55 ml, 2 ¼ inches diameter by 2 ½ inches length) with three ~10.75-g tungsten carbide balls.…”

“…Synthesis was adapted from the literature ( 3 , 30 ). First, it was experimentally determined that the Yb 14 MgSb 11 end member required 14.02Yb:1.2Mg:Sb11 to obtain a phase pure product.…”

“…Also anomalous, the thermal conductivity of Yb 14 MnSb 11 ( 23 ), Yb 14 MgSb 11 ( 26 ), Sr 14 MgSb 11 ( 27 ), and Eu 14 MgSb 11 ( 27 ) and other doped compositions of Yb 14 MnSb 11 have an unexplained increase from ~300 to ~600 K. At 300 K, Yb 14 MnSb 11 is above its Debye temperature ( 28 ), so the lattice thermal conductivity is expected to decrease proportionally as 1/ T if Umklapp scattering dominates phonon transport, or temperature independent if diffusion ( 29 ) dominated. This would imply that the increase must come from the electronic portion of thermal conductivity; yet, an estimation of the electronic thermal conductivity results in a decreasing trend with increasing temperature ( 3 , 26 , 27 , 30 ). A similar low temperature increase in thermal conductivity is also unexplained in RE 3− x Te 4 ( RE = Nd, La) ( 31 ), SnTe ( 32 ), Ag 9 AlSe 6 ( 33 ), and Eu 9 CdSb 9 ( 34 ).…”

Synthesis-enabled exploration of chiral and polar multivalent quaternary sulfides

“…Lowering of the reaction temperature to stabilize complex metastable or stable compounds is a common goal for solid state synthesis, [2][3][4][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] such as formation of metastable forms of RE oxychlorides via low-temperature pyrohydrolysis of (NH4)3REC16. 49 The mixing of the rare-earth and transition metals in the silicide precursors is somewhat akin to eutectic fluxes used in the Latturner group to make metal-rich intermetallics, [29][30][31][32][33][34] as well as flux syntheses of complex intermetallics performed by other groups.…”

“…49 The mixing of the rare-earth and transition metals in the silicide precursors is somewhat akin to eutectic fluxes used in the Latturner group to make metal-rich intermetallics, [29][30][31][32][33][34] as well as flux syntheses of complex intermetallics performed by other groups. [2][3][4][35][36][37][38][39][40][41][42][43][44][45][46][47][48] In-situ powder X-ray diffraction study was used to elucidate the mechanism of formation of such quaternaries. Detailed structural characterization by single crystal X-ray diffraction and 29 Si and 45 Sc solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies are reported.…”