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The structure, magnetic properties, and 151 Eu and 119 Sn Mossbauer spectra of the solid-solution Eu 11−x Sr x Zn 4 Sn 2 As 12 are presented. A new commensurately modulated structure is described for Eu 11 Zn 4 Sn 2 As 12 (R3m space group, average structure) that closely resembles the original structural description in the monoclinic C2/c space group with layers of Eu, puckered hexagonal Zn 2 As 3 sheets, and Zn 2 As 6 ethane-like isolated pillars. The solid-solution Eu 11−x Sr x Zn 4 Sn 2 As 12 (0 < x < 10) is found to crystallize in the commensurately modulated R3 space group, related to the parent phase but lacking the mirror symmetry. Eu 11 Zn 4 Sn 2 As 12 orders with a saturation plateau at 1 T for 7 of the 11 Eu 2+ cations ferromagnetically coupled (5 K) and shows colossal magnetoresistance at 15 K. The magnetic properties of Eu 11 Zn 4 Sn 2 As 12 are investigated at higher fields, and the ferromagnetic saturation of all 11 Eu 2+ cations occurs at ∼8 T. The temperature-dependent magnetic properties of the solid solution were investigated, and a nontrivial structure−magnetization correlation is revealed. The temperature-dependent 151 Eu and 119 Sn Mossbauer spectra confirm that the europium atoms in the structure are all Eu 2+ and that the tin is consistent with an oxidation state of less than four in the intermetallic region. The spectral areas of both Eu(II) and Sn increase at the magnetic transition, indicating a magnetoelastic effect upon magnetic ordering.

Here we report the synthesis and characterization of three quaternary complex chalcogenides, Ag0.72Bi5.48Cu0.88S9 (I), Ag0.70Bi5.30Cu1.3S9 (II), Ag0.34Bi4.54Cu1.98PbS9 (III). All the compounds in this homologous series crystallize in the C2/m space...

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Layered Zintl phases with A2MPn2 stoichiometry are an underexplored class of potential thermoelectric materials with complex and diverse chemistry. The solid solution Yb2–x Eu x CdSb2 is an example of the promise these compounds hold, as one composition, Yb1.64Eu0.36CdSb2, has reported one of the highest zTs of any Zintl phase material at 525 K. The present study examines changes in structure and bonding of this solid solution that impacts thermoelectric performance. Pair distribution function analysis is combined with electronic structure modeling to take a chemical bonding-based approach to deconvolute the impact of defects on thermal and electronic properties in Yb2–x Eu x CdSb2. Yb2–x Eu x CdSb2 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) samples were synthesized, and thermoelectric properties and defect chemistry were investigated. Samples from the middle of the series x = 0.2 and 0.3 were found to be the most highly defected, exhibiting Yb and Sb vacancies, as well as distortions in the Yb–Sb coordination spheres that correlate with thermoelectric properties. The highest efficiency is reported for x = 0.4 (zT ≈ 0.9 at 525 K), and the thermoelectric quality factor predicts that x = 0.3 could achieve zT > 2 by synthetically tuning the defect structure and thereby carrier concentration. The strategy of investigating local structure outlined in this study can be applied to a variety of other thermoelectric materials to provide insight into the hidden role of defect chemistry in understanding the structure–property relationships in extended solids.