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The efficiency of thermoelectric materials is directly related to the dimensionless figure of merit ZT=S2σκT, therefore, one of the means to improve ZTis to reduce the thermal conductivity. Our research focuses on half‐Heusler superlattices (SLs) and the relationship between the SL period and the thermal conductivity. The cross‐plane thermal conductivity of DC‐sputtered TiNiSn/HfNiSn SLs was measured by the 3ωmethod at room temperature and a clear reduction of κwas achieved for all SL periods, in particular for periods smaller than 20 nm. Moreover, the thermal conductivities of TiNiSn and HfNiSn single films display reduced values compared to the literature data for bulk materials. Furthermore, we also found that the quality of interfaces has an influence on κ, namely, SLs with rougher interfaces exhibit an about 20% lower thermal conductivity compared to samples with sharp interfaces.

Semiconducting half‐Heusler compounds based on NiSn and CoSb have attracted attention because of their good performance as thermoelectric materials. Nanostructuring of the materials was experimentally established through phase separation in (T1−x′Tx″)T(M1−yMy′)alloys when mixing different transition metals (T, T′, T″) or main group elements (M, M′). The electric transport properties of such alloys depend not only on their micro‐ or nanostructure but also on the atomic‐scale electronic structure. In the present work, the influence of the band structure and density of states on the electronic transport and thermoelectric properties is investigated in detail for the constituents of phase‐separated half‐Heusler alloys. The electronic structure is calculated using different theoretical schemes for ordered and disordered materials. It is found that chemical disorder scattering influences the electronic transport properties in all substituted materials. Substitution in NiSn‐based compounds leads to high performance n‐type materials but only moderate p‐type thermoelectric properties. The latter is caused by the influence of the valence band on the conductivity. For CoSb‐based compounds, it is found that Sb substitution with Sn keeps the bands close to the Fermi energy intact. The resulting substituted alloys are excellent p‐type materials because of the characteristic valence band structure in the Λdirection. The figure shows the fcccrystal structure (C1b) of the half‐Heusler compounds (prototype: MgAgAs, cF12, F:4‾3m, 216).

Sb‐substituted Cs2AgBiBr6single crystals and powders are synthesized by various wet‐chemical routes as well as by solvent‐free mechanochemical synthesis. Phase purity and resulting optical properties of differently synthesized Sb‐substituted Cs2AgBiBr6absorbers are investigated and compared. X‐ray diffraction confirms that Sb substitution results in an apparent single‐phase formation with a unit cell shrinkage up to a certain substitution limit, which varies depending on the synthesis routes. Questions about the phase identification determined by X‐ray diffraction are raised and thoroughly investigated by Raman spectroscopy. UV–vis spectroscopy reveals that Sb3+substitution induces a reduction in the optical bandgap of Cs2AgBiBr6, whereas octahedral factor calculations provide that SbBr6octahedra can be hardly stable in a Cs2AgBiBr6double perovskite. The experimental results of the occurrence and evolution of Raman bands and theoretical calculations of the structural stability of SbBr6octahedra in Cs2AgBiBr6unambiguously raise doubts about the Sb‐substitution feasibility in Cs2AgBiBr6, and a general substitution strategy in Cs2AgBiBr6is discussed. For the purpose of phase identification of the Sb‐substituted Cs2AgBiBr6, Raman spectroscopy is a better choice than diffraction analysis because the X‐ray diffraction diffraction patterns of Cs3Sb2Br9and Cs3Bi2Br9directly overlap with Cs2AgBiBr6.

A thermodynamically stable phase separation of Co2Dy0.5Mn0.5Sn into the Heusler compound Co2MnSn and Co8Dy3Sn4is induced by rapid cooling from the liquid phase. The phase separation forms an ordered flower‐like structure on the microscale. The increased scattering of phonons at the phase boundaries reduces the thermal conductivity and thus improves thermoelectric and spincaloric properties.

We report the quaternary Heusler compound derivatives CoFe1+xTi1–xAl and CoMn1+xV1–xAl, which do not have centers of inversion. Classical T2T′M (T, T′ = transition metal, M = main group element) Heusler compounds (prototype: Cu2MnAl) crystallize in the L21structure, space group Fm$\bar {3}$m(225) that exhibits a center of inversion. Replacing one of the T2atoms by another transition element (T″) results in a quaternary TT′T″M compound with F$\bar {4}$3msymmetry (Y; structure type LiMgPdSn) without center of inversion. In the case of “quasi closed shell” compounds with 24 valence electrons in the primitive cell, one expects the absence of ferromagnetism according to the Slater–Pauling rule. Increasing the number of valence electrons will allow a study of the onset of the magnetic ground state. In this work, CoFeTiAl and isovalent CoMnVAl as well as the accompanying solid solutions CoFe1+xTi1–xAl and CoMn1+xV1–xAl were synthesized and their structure and magnetic properties investigated. CoMn1+xV1–xAl (x> 0) is a half‐metallic ferrimagnet in which the magnetic ground state is controlled by the strong localized moment at the Mn atoms replacing V.

Co2‐based Heusler compounds with 27.8 valence electrons exhibit an exceptional electronic structure that makes them interesting materials for the application in spintronics. Co2Cr0.6Fe0.4Al is the most prominent example of this particular family of compounds. In this article new materials of this class are tested with respect to their structural and magnetic properties. X‐ray diffraction, Mössbauer spectroscopy, energy dispersive X‐ray spectroscopy, and SQUID magnetometry were carried out to characterize the compounds. The use of Co2Fe0.45Ti0.55Ge as a new material in spintronic devices is suggested.

Heusler compounds are promising materials in many fields of contemporary research. The spectrum of their possible applications ranges from magnetic and magneto‐mechanical materials over semiconductors and thermoelectrics to superconductors. An important feature of the Heusler compounds is the possibility of controlling the valence electron concentration by partial substitution of elements. On the other hand, the properties also depend on the degree of ordering of the crystal structure. In general, Heusler compounds crystallize in the Cu2MnAl‐type structure but in many cases certain types of disorder are observed. In this paper a detailed description of the different types of disordered structures is given. Additionally, the synthesis of new Heusler compounds is reported. The prepared compounds contain ternary Cr‐, Rh‐,Ru‐, Ni‐, Pd‐, and Pt‐based Heusler systems as well as quaternary Co2‐based compounds and compounds of the general formula XX′YZ. The crystal structure was determined by XRD measurements and the structural ordering of the compounds is discussed.

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Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure–property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.

Spintronik ist ein multidisziplinäres Forschungsfeld zwischen Physik, Material- und Ingenieurwissenschaften, aber auch ein neuer Forschungsbereich der Festkörperforschung. Für die verschiedensten Anforderungen müssen unterschiedlichste Materialien gefunden werden. Die Suche nach ferromagnetischen Halbleitern und stabilen halbmetallischen Ferromagneten mit Curie-Temperaturen höher als Raumtemperatur ist immer noch eine zentrale Aufgabe für die Festkörperchemie. Ein allgemeines Verständnis der Struktur-Eigenschafts-Beziehungen ist eine notwendige Voraussetzung für das Design neuer Materialien. In diesem Aufsatz werden die wichtigsten Entwicklungen im Bereich der Spintronik aus der Perspektive des Materialwissenschaftlers dargestellt.

The half-Heusler (HH) compound NbCoSn with 18 valence electrons is a promising thermoelectric (TE) material due to its appropriate electrical properties as well as its suitable thermal and chemical stability. Nowadays, doping/substitution and tailoring of microstructures are common experimental approaches to enhance the TE performance of HH compounds. However, detailed theoretical insights into the effects of doping on the microstructures and TE properties are still missing. In this work, the microstructure of NbCoSn was tailored through precipitating the full-Heusler phases in the matrix by changing the nominal ratio of Co and Ni on the Co sites, focusing on the resulting TE properties. Further, first-principles calculations were employed to understand the relationship between the microstructure and the TE properties from the thermodynamic point of view. Detailed analysis of the electronic structure reveals that the presence of excess Co/Ni contributes to the increasing carrier concentration. Through an increase in the electrical conductivity and a reduction in the thermal conductivity, the TE performance is improved. Therefore, the present work offers a new pathway and insights to enhance the TE properties by modifying the microstructure of HH compounds via tailoring the chemical compositions.

On page 1822, Benjamin Balke and co‐workers report the thermodynamically stable phase separation of a Heusler compound induced by rapid cooling from the liquid phase. A linear combination of the different element‐specific energy‐dispersive X‐ray (EDX) mappings (with brightness proportional to the concentration) is shown. The phase separation forms an ordered 3D flower‐like structure on the microscale.