From3DIntermetallic Antiperovskites to2DHalf Antiperovskites

Abstract

The concept of ordered half antiperovskites (HAP) derives A 2 M 3 X 2 structures formally from metal‐rich intermetallic antiperovskites AM 3 X such as MgNi 3 C. It was developed within the last decade in Regensburg accompanied by fascinating discoveries of other groups. It extends the idea known for oxide structures related to perovskite such as cuprate superconductors: therein, the 3D M‐O network is cut to 2D sheets, that is YBaCu 2 O 7‐d . By systematic formation of unoccupied sites 3D interlinked MO 6 octahedra in perovskites are cut to 2D substructures with CuO 4 and CuO 5 units. To the best of our knowledge, a similar scheme was not described for antiperovskites AM 3 X, where X and M sites of perovskites are exchanged. MgNi 3 C is taken subsequently as reference example. First reported by Hütter and Stadelmaier it became famous as noncuprate nonoxide superconductor. We show that MX 6 and XM 6 units in perovskites AMX 3 and APs AM 3 X can be cut to MX 3 and XM 3 units to form 2D structures. The situation compares to gray As and black P that are derived from a primitive α‐Po structure by cutting three of the six bonds. In both cases, interlinked 3D networks are cut to 2D structures. However, the ternary compounds introduce additional degrees of freedom by varying the electron count by composition that turns out important to design properties such as for example magnetism and thermoelectrics of superconductivity. Consequently, the HAP concept consists of a crystal structure part for compounds A 2 M 3 X 2 = AM 3/2 L 3/2 X with AP superstructures and an electronic structure part. In this review, we point out relations to antiperovskite AM 3 X crystal and electronic structures, the history of A 2 M 3 X 2 compounds, the HAP concept, important discoveries of HAP materials and novel investigations on synthesis, spintronics, thermoelectrics, superconductors, and topological properties. Advantages of the given conceptual view are pointed out for computer modeling, design, and prediction of structures and functions.

Von der Laborpresse zu Spins mit riesigen Effekten

“…Der Cobalt-haltige Stempel der Presse hatte mit InS reagiert. [2,3,6] Die strukturellen Besonderheiten des Sn 2 Co 3 S 2 sind mit diesem Modell leicht zu verstehen. Letzteres hatte Ramdohr 1949 in Australien entdeckt, Shandit genannt und die hoch anisotrope trigonale Struktur (Raumgruppe R " 3m) bei gleichzeitig pseudo-kubischer Metrik beschrieben (siehe Lit.…”

“…[6] Der GMR-Effekt bewies bereits,w ie aus Grundlagenforschung High-Tech-Anwendungen entstanden. Letztere finden sich auf einer Kurve entweder hoher Hall-Leitfähigkeiten bei niedrigen Hall-Winkeln (z.…”

“…Der gemessene Hall-Winkel von s AH / s x = 20 %b edeutet, dass eine niedrige Leitfähigkeit s x eines Semimetalls bei gleichzeitig hoher anomaler Hall-Leitfähigkeit s AH > 10 3 Scm À1 wie in Eisen (s AH /s x = 2.5 %) vorliegt. Beide Gruppen weisen als Ursache die elektronische Topologie eines magnetischen Weyl-Semimetalls im 2001 vorhergesagten S = 1 = 2 -Zustand [2,3] [2,3,6] Die strukturellen Besonderheiten des Sn 2 Co 3 S 2 sind mit diesem Modell leicht zu verstehen. In den CoS 2 Sn 4 -Polyedern Abbildung 1.…”

“…Sn 2 Co 3 S 2 ragt demgegenüber wie ein einsamer Stern mit grçßtem gemessenem Hall-Winkel von s AH /s = 20 %b ei sehr hoher Hall-Leitfähigkeit von bei s AH > 1.1 10 3 Scm À1 heraus.Die Ergebnisse zeigen, welches Potential in der Verknüpfung neuer topologischen Materialien mit anderen Funktionen steckt, vor allem mit magnetischen und Spintronik-Materialien. [6] Der GMR-Effekt bewies bereits,w ie aus Grundlagenforschung High-Tech-Anwendungen entstanden. Man darf gespannt sein, welche faszinierenden Eigenschaften als nächstes fürandere magnetische Weyl-Halbmetalle und speziell fürS n 2 Co 3 S 2 berichtet werden, z.…”

From Laboratory Press to Spins with Giant Effects

“…Sn 2 Co 3 S 2 was first prepared by Zabel et al in 1979, [5] when they found isotypic In 2 Co 3 S 2 from high pressure investigations on indium sulfide.T he stamp of the press contained cobalt and reacted with InS.Zabel and Range and co-workers found that both 2:3:2C oa nd the homologous nickel compounds crystallized in isotypic structures of the mineral Pb 2 Ni 3 S 2 .T he latter was discovered by Ramdohr in 1949 in Australia, who called it shandite and described already its highly anisotropic structure of space group R " 3m with pseudo cubic metrics. [2,6] ForSn 2 Co 3 S 2 this is visualized in Figure 1by its primitive Sn substructure that is centered by Sa toms. Significant bonding is however formed by Co atoms in half of the Sn 4 faces,that is,face-sharing S 2 Sn 4 polyhedra.…”