as an interdisciplinary research line of chemistry, physics, and materials engineering. [1,2] Numerous scientific efforts have focused on designing new materials with the desired electronic and magnetic features by tuning the chemical composition, structural parameters, and physical modifications. [3,4] In recent years, defect variant structures have been considered as promising candidates to provide new, targeted properties and property combinations. The interdependence of magnetic and electronic structures to the partial vacancies on anion positions has been reported for a few ferrite and ferrate compounds indicating significant effects of vacancies on the Fermi level, orbital splitting, and geometrical interactions in the crystal structure, thereby changing the magnetization and the ionic conductivity. [5,6] The change in properties originates from the different vacancies of isolated cations and anions, as well as defects in the complex anionic motifs. For compounds including iron, depending on the structure, the iron vacancies can be considered either as vacancies of single cations, or as defects in the anionic motifs. Although the impact of iron The multigram synthesis of K 2 [Fe 3 S 4 ] starting from K 2 S and FeS is presented, and its electronic and magnetic properties are investigated. The title compound obtains a defect variant of the K[Fe 2 Se 2 ] structure type. Dielectric and impedance measurements indicate a dielectric constant of 1120 at 1 kHz and an outstanding ionic conductivity of 24.37 mS cm -1 at 295 K, which is in the range of the highest reported value for potential solid-state electrolytes for potassium-ion batteries. The Seebeck coefficient of the n-type conductor amounts to −60 µV K −1 at 973 K. The mismatch of the measured electrical resistivity and the predicted metal-like band structure by periodic quantum chemical calculations indicates Mott insulating behavior. Magnetometry demonstrates temperature-dependent, large exchange bias fields of 35 mT, as a consequence of the coexistence of spin glass and antiferromagnetic orderings due to the iron vacancies in the lattice. In addition, the decreasing training effects of 34% in the exchange bias are identified at temperatures lower than 20 K. These results demonstrate the critical role of iron vacancies in tuning the electronic and magnetic properties and a multifunctional material from abundant and accessible elements.

Cu2Se is a high ZT material consisting of cheap and earth abundant elements. Its high thermoelectric performance is mainly based on very low thermal conductivity associated with mobile atoms. This comes with the drawback of a critical voltage, over which the material decomposes to elemental copper and a copper-deficient Cu2−xSe phase. Composites of copper selenide with graphite do not enhance the critical voltage significantly as copper selenide is not completely encapsulated by graphite. Thermoelectric properties of pellets of such composites obtained by mixing and pressing Cu2Se powder and graphite flakes are comparable to pristine Cu2Se, but thermal stability increases remarkably. Samples with different grain sizes show that the reproducibility of measurements is worse for larger grains, which in addition lead to inferior thermoelectric performance. Higher graphite contents increase both thermal and electrical conductivity, and an optimum of the thermoelectric figure of merit ZT is observed for fine-grained samples with 4 wt. % graphite.

The structure of the new compound GaGe2Te has been determined using nanofocused synchrotron radiation. The trigonal structure (space group P m1, a=4.0443(3) Å, c=14.923(2) Å, V=211.38(4) Å3; Z=2) consists of Ge bilayers sandwiched by Ga−Te layers. Ge and Ga are tetrahedrally coordinated. The layer packages are separated by a van der Waals gap with a Te−Te distance of 4.1502(7) Å. The structure resembles that of GaGeTe but features an additional Ge atom layer. Despite small scattering contrast of Ga and Ge, precise high‐resolution data enable unequivocal atom assignment as confirmed by R values of different models. DFT calculations suggest only a small extent of charge transfer, which is confirmed by both Bader and Mulliken charges. Thus, bonding within the layer packages is predominantly covalent, especially between Ga and Ge. Formal oxidation states according to GaIIIGe(0)Ge−ITe−II, i. e. assuming rather ionic Ge−Ga bonds, convey a much less realistic situation than GaIIGe2(0)Te−II, which is in line with GaGeTe.

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