ABSTRACT
The complex metal-rich boride Ti5-xFe1-yOs6+x+yB6 (0 < x,y < 1), crystallizing in a new structure type (space group Cmcm, no. 63), was prepared by arc-melting. The new structure contains both isolated boron atoms and zigzag boron chains (B-B distance of 1.74 Å), a rare combination among metal-rich borides. In addition, the structure also contains Fe-chains running parallel to the B-chains. Unlike in previously reported structures, these Fe-chains are offset from each other and arranged in a triangular manner with intrachain and interchain distances of 2.98 and 6.69 Å, respectively. Density functional theory (DFT) calculations predict preferred ferromagnetic interactions within each chain but only small energy differences for different magnetic interactions between them, suggesting a potentially weak long-range order. This new structure offers the opportunity to study new configurations and interactions of magnetic elements for the design of magnetic materials.
ABSTRACT
In the quest for materials addressing the grand challenges of the future, there is a critical need for a broad understanding of their electronic structures because the knowledge of the electronic structure of a given solid allows us to recognize its structural preferences and to rationalize its properties. As previous research on quaternary chalcogenides containing active metals (a group-I- or -II-element), early transition-metals, and late transition-metals indicated that such materials could pose as alluring systems in the developments of thermoelectrics, our impetus was stimulated to probe the suitability of tellurides belonging to the prolific A3R4Cu5Te10-family. In doing so, we first used quantum-chemical techniques to explore the electronic and vibrational properties of representatives crystallizing with different A3R4Cu5Te10 structure types. The outcome of these explorations indicated that the aspects that control the formation of a given type of A3R4Cu5Te10 structure are rather subtle so that transitions between different types of A3R4Cu5Te10 structures could be induced by manipulating the ambient conditions. To probe this prediction, we explored the thermal behavior for the example of one quaternary telluride, that is, Rb3Er4Cu5Te10, and thereby identified a new type of A3R4Cu5Te10 structure. Because understanding the structural features of the A3R4Cu5Te10 family plays an important role in the analyses of the aforementioned explorations, we also present an overview about the structural features and the members of this class of quaternary tellurides. In this connection, we also provide a structural report of four tellurides, that is, K3Tb4Cu5Te10 and Rb3R4Cu5Te10 (R = Tb, Dy, Ho), which have been obtained from high-temperature solid-state reactions for the very first time.
ABSTRACT
Differing reports regarding the structural features of the mineral stützite, Ag5-xTe3 (-0.25 ≤ x ≤ 1.44), and the quest for tellurides with low-dimensional fragments stimulated our impetus to review this system by employing experimental as well as quantum-chemical methods. Determination of the crystal structures for three samples with compositions Ag4.72(3)Te3 (I), Ag4.66(1)Te3 (II), and Ag4.96(2)Te3 (III) revealed considerable positional disorders for the Ag and Te sites and previously unknown structure models for I and II, which differ from that of III through the stacking sequences of honeycomb-fashioned Te layers. The crystal structures comprise [Te@Ag9]@Te14 units in the forms of bicapped hexagonal Te antiprisms that enclose Te-centered tricapped trigonal Ag prisms, while each Te atom is encapsulated by Ag atoms assembling diverse types of coordination polyhedra. The vibrational and electronic properties were determined for three models approximating the actual crystal structure of stützite by means of techniques based on first principles. From analyses of the electronic structures and projected crystal orbital Hamilton populations (pCOHP), it is clear that the amounts and distributions of the Ag atoms within the Te network should be influenced by the subtle interplay between the attempts to achieve an electronically favorable situation with a gap at EF and minimize the occupations of antibonding states.
