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1. The impact of site selectivity and disorder on the thermoelectric properties of Yb ₂₁ Mn ₄ Sb ₁₈ solid solutions: Yb ₂₁ Mn _4−x Cd _x Sb ₁₈ and Yb _21−y Ca _y Mn ₄ Sb ₁₈

   https://doi.org/10.1039/d1ma00497b  

   He, Allan; Cerretti, Giacomo; Kauzlarich, Susan M. (August 2021, Materials Advances)

   Thermoelectric materials can convert heat into electricity. They are used to generate electricity when other power sources are not available or to increase energy efficiency by recycling waste heat. The Yb 21 Mn 4 Sb 18 phase was previously shown to have good thermoelectric performance due to its large Seebeck coefficient (∼290 μV K −1 ) and low thermal conductivity (0.4 W m −1 K −1 ). These characteristics stem respectively from the unique [Mn 4 Sb 10 ] 22− subunit and the large unit cell/site disorder inherent in this phase. The solid solutions, Yb 21 Mn 4− x Cd x Sb 18 ( x = 0, 0.5, 1.0, 1.5) and Yb 21− y Ca y Mn 4 Sb 18 ( y = 3, 6, 9, 10.5) have been prepared, their structures characterized and thermoelectric properties from room temperature to 800 K measured. A detailed look into the structural disorder for the Cd and Ca solid solutions was performed using synchrotron powder X-ray diffraction and pair distribution function methods and shows that these are highly disordered structures. The substitution of Cd gives rise to more metallic behavior whereas Ca substitution results in high resistivity. As both Cd and Ca are isoelectronic substitutions, the changes in properties are attributed to changes in the electronic structure. Both solid solutions show that the thermal conductivities remain extremely low (∼0.4 W m −1 K −1 ) and that the Seebeck coefficients remain high (>200 μV K −1 ). The temperature dependence of the carrier mobility with increased Ca substitution, changing from approximately T −1 to T −0.5 , suggests that another scattering mechanism is being introduced. As the bonding changes from polar covalent with Yb to ionic for Ca, polar optical phonon scattering becomes the dominant mechanism. Experimental studies of the Cd solid solutions result in a max zT of ∼1 at 800 K and, more importantly for application purposes, a ZT avg ∼ 0.6 from 300 K to 800 K. 

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

   https://doi.org/10.1126/sciadv.abe9439  

   Perez, Christopher J.; Wood, Maxwell; Ricci, Francesco; Yu, Guodong; Vo, Trinh; Bux, Sabah K.; Hautier, Geoffroy; Rignanese, Gian-Marco; Snyder, G. Jeffrey; Kauzlarich, Susan M. (January 2021, Science Advances)

   null (Ed.)

   The Zintl phases, Yb 14 M Sb 11 ( M = Mn, Mg, Al, Zn), are now some of the highest thermoelectric efficiency p-type materials with stability above 873 K. Yb 14 MnSb 11 gained prominence as the first p-type thermoelectric material to double the efficiency of SiGe alloy, the heritage material in radioisotope thermoelectric generators used to power NASA’s deep space exploration. This study investigates the solid solution of Yb 14 Mg 1− x Al x Sb 11 (0 ≤ x ≤ 1), which enables a full mapping of the metal-to-semiconductor transition. Using a combined theoretical and experimental approach, we show that a second, high valley degeneracy ( N v = 8) band is responsible for the groundbreaking performance of Yb 14 M Sb 11 . This multiband understanding of the properties provides insight into other thermoelectric systems (La 3− x Te 4 , SnTe, Ag 9 AlSe 6 , and Eu 9 CdSb 9 ), and the model predicts that an increase in carrier concentration can lead to zT > 1.5 in Yb 14 M Sb 11 systems. 

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3. Flux Growth of La ₃ MC ₂ ( M  = Sb, Bi, Te), a New Family of Ternary Carbides

   https://doi.org/10.1002/zaac.202500046  

   Marzano, Luke; Uddin, Mohammed Sahab; Zareihassangheshlaghi, Amirhossein; Araoyinbo, Olufemi; Hernandez, Juan; Latturner, Susan (July 2025, Zeitschrift für anorganische und allgemeine Chemie)

   Reactions of carbon with a heavy main group metal (M = Sb, Bi, or Te) in an excess of lanthanum/nickel eutectic flux lead to formation of a family of carbide compounds La₃MC₂with a new structure type. The monoclinic structure features C₂⁴⁻anions octahedrally coordinated by six La³⁺cations, andManions surrounded by 8 La³⁺cations. These compounds are not charge‐balanced and lie on the border between intermetallic carbides and mixed anion salts. Density of states calculations show a pseudogap at the Fermi level for La₃BiC₂, which indicates that this compound is a poor metal with optimized LaBi bonding interactions. 

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4. Ca ₂ Ga ₄ Ge ₆ and Ca ₃ Ga ₄ Ge ₆ : Synthesis, Structure, and Electronic Properties

   https://doi.org/10.1002/zaac.202100342  

   Hodge, Kelsey L; Davis, H Olivia; Koster, Karl G; Windl, Wolfgang; Moore, Curtis E; Goldberger, Joshua E (August 2022, Zeitschrift für anorganische und allgemeine Chemie)

   Abstract During the search for transition metal‐free alkyne hydrogenation catalysts, two new ternary Ca−Ga−Ge phases, Ca₂Ga₄Ge₆(Cmc2₁, a=4.1600(10) Å, b=23.283(5) Å, c=10.789(3) Å) and Ca₃Ga₄Ge₆(C2/m, a=24.063(2) Å, b=4.1987(4) Å, c=10.9794(9) Å, β=91.409(4)°), were discovered. These compounds are isostructural to the previously established Yb₂Ga₄Ge₆and Yb₃Ga₄Ge₆analogues, and according to Zintl‐Klemm counting rules, consist of anionic [Ga₄Ge₆]⁴⁻and [Ga₄Ge₆]⁶⁻frameworks in which every Ga and Ge atom would have a formal octet with no Ga−Ga or Ga−Ge π‐bonding. These compounds are metallic, based on temperature dependent electrical resistivity and thermopower measurements for Ca₃Ga₄Ge₆, along with density functional theory calculations for both phases. Unlike the highly active 13‐layer trigonal CaGaGe phase, these new compounds exhibit minimal activity in the semi/full alkyne hydrogenation of phenylacetylene, which is consistent with previous observations that the lack of a formal octet for framework atoms is essential for catalysis in these Zintl‐Klemm compounds. 

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5. Chemically driven superstructural ordering leading to giant unit cells in unconventional clathrates Cs ₈ Zn ₁₈ Sb ₂₈ and Cs ₈ Cd ₁₈ Sb ₂₈

   https://doi.org/10.1039/D0SC03846F  

   Owens-Baird, Bryan; Yox, Philip; Lee, Shannon; Carroll, Xian B.; Grass Wang, Suyin; Chen, Yu-Sheng; Lebedev, Oleg I.; Kovnir, Kirill (September 2020, Chemical Science)

   null (Ed.)

   The unconventional clathrates, Cs 8 Zn 18 Sb 28 and Cs 8 Cd 18 Sb 28 , were synthesized and reinvestigated. These clathrates exhibit unique and extensive superstructural ordering of the clathrate-I structure that was not initially reported. Cs 8 Cd 18 Sb 28 orders in the Ia 3̄ d space group (no. 230) with 8 times larger volume of the unit cell in which most framework atoms segregate into distinct Cd and Sb sites. The structure of Cs 8 Zn 18 Sb 28 is much more complicated, with an 18-fold increase of unit cell volume accompanied by significant reduction of symmetry down to P 2 (no. 3) monoclinic space group. This structure was revealed by a combination of synchrotron X-ray diffraction and electron microscopy techniques. A full solid solution, Cs 8 Zn 18−x Cd x Sb 28 , was also synthesized and characterized. These compounds follow Vegard's law in regard to their primitive unit cell sizes and melting points. Variable temperature in situ synchrotron powder X-ray diffraction was used to study the formation and melting of Cs 8 Zn 18 Sb 28 . Due to the heavy elements comprising clathrate framework and the complex structural ordering, the synthesized clathrates exhibit ultralow thermal conductivities, all under 0.8 W m −1 K −1 at room temperature. Cs 8 Zn 9 Cd 9 Sb 28 and Cs 8 Zn 4.5 Cd 13.5 Sb 28 both have total thermal conductivities of 0.49 W m −1 K −1 at room temperature, among the lowest reported for any clathrate. Cs 8 Zn 18 Sb 28 has typical p-type semiconducting charge transport properties, while the remaining clathrates show unusual n–p transitions or sharp increases of thermopower at low temperatures. Estimations of the bandgaps as activation energy for resistivity dependences show an anomalous widening and then shrinking of the bandgap with increasing Cd-content. 

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