Revealing the Nature of Bonding in Rare‐Earth Transition‐Metal Tellurides by Means of Methods Based on First Principles

Abstract

Tellurium-rich rare-earth (R) transition-metal tellurides with low-dimensional Te networks provide alluring systems to explore the formations of charge density waves (CDWs). The lack of knowledge concerning the bonding in Te-rich rare-earth transition-metal tellurides inspired us to determine the electronic structures and the nature of bonding for two prototypical examples, namely LaCu 0.28 Te 2 and Gd 3 Cu 2 Te 7 , by means of methods based on first principles. From chemical bonding anal- [a]

Revealing the Nature of Chemical Bonding in an ALn2Ag3Te5-Type Alkaline-Metal (A) Lanthanide (Ln) Silver Telluride

“…Under consideration of previous research [37,38] on the electronic structures of alkaline-metal-containing polar intermetallics, this outcome suggests that the Rb-Te interactions should be considered as ionic interactions, while the Pr-Te and Ag-Te interactions should be regarded as rather strong, polar, mixed-metal bonds. This outcome also indicates that a full valence-electron transfer as proposed by an application of the Zintl-Klemm concept should be regarded with suspicion-a consequence which has also been identified by recent explorations of the electronic structures of rare-earth transition-metal tellurides [22] as well as silver tellurides [21]. The homoatomic Ag-Ag interactions change from bonding to considerable antibonding states at −4.41 eV, which may be regarded as attributes of the d 10 -d 10 closed-shell [39,40] interactions; however, the Ag-Ag -ICOHP values are indicative of a net bonding character for these interactions.…”

“…To provide an insight into the bonding situation in RbPr2Ag3Te5, we followed up with an examination of the crystal orbital Hamilton population curves (COHP; Figure 2) and their respective integrated values (Table 3). In this context, the cumulative -ICOHP/cell values, i.e., the sums of the negative ICOHP/bond values of all nearest neighboring contacts within one unit cell, were projected as percentages of the net bonding capabilities for each sort of interaction to identify roles of the diverse interactions in overall bonding-a procedure that has been largely employed elsewhere [21,22,[33][34][35][36]. (Figure 2) reveals that the occupied states close to the Fermi level, E F , originate to a large extent from the Ag-d and Te-p atomic orbitals beside minor contributions from the Pr-d states.…”

“…The distributions of the valence-electrons in the tellurides have been typically described by applying the Zintl-Klemm concept [19,20]; however, the application of the latter to certain tellurides containing low-dimensional tellurium fragments resulted in the assignments of non-electron-precise charges to the tellurium atoms [20]. In that connection, recent research [21,22] on the electronic structures of certain tellurides, i.e., LaCu x Te 2 (0.28 ≤ x ≤ 0.50), Gd 3 Cu 2 Te 7 , and Ag 5−x Te 3 (−0.25 ≤ x ≤ 1.44), indicated that the valence-electron transfers as suggested by Zintl-Klemm treatments should be taken with a grain of salt. In fact, analyzing the nature of bonding for the aforementioned tellurides revealed the presence of strong rare-earth-tellurium as well as transition-metal-tellurium bonding interactions being in stark contrast to the (complete) valence-electron transfers as assumed by Zintl-Klemm treatments.…”

Revisiting the Zintl‒Klemm Concept for ALn2Ag3Te5-Type Alkaline-Metal (A) Lanthanide (Ln) Silver Tellurides

“…In the light of such relevance for research and technical applications, one could also expect that the nature of bonding in tellurides is typically examined employing first-principles-based approaches; yet, the electronic structures, particularly the nature of bonding, in many tellurides are frequently (and simplistically) interpreted by applying the Zintl-Klemm concept rather than first-principles-based bonding analyses [15]. More recent research [16][17][18] on the electronic structures of certain tellurides, however, demonstrated that such Zintl-Klemm pictures should be taken with a pinch of salt. In fact, examining the electronic structures of (active-metal) transition-metal tellurides (active-metal = group I and III elements) revealed that the bonding nature in these tellurides is dominated by strong transition-metal−tellurium interactions beside minor transition-metal−transition-metal or tellurium−tellurium interactions.…”

Revealing Tendencies in the Electronic Structures of Polar Intermetallic Compounds

“…Additional inspections of the X-ray diffraction patterns of SmCu0.34Te2 being isostructural with LaCuxTe2 (0.28 ≤ x ≤ 0.50) bared the presence of weak reflections pointing to a superstructure along the direction of the linear tellurium chains. Recent quantum chemical examinations [124] on the nature of bonding in these rare-earth copper tellurides showed the paramount role of heteroatomic R-Te bonding for these materials; however, the degrees of distortions within the linear tellurium chains appear to be influenced by the amounts of copper in the tellurides: a gedankenexperiment demonstrates that the Te chains can distort, a gap opens at the Fermi level and the overall bonding is maximized as the copper content is reduced. Another example of a telluride whose electronic structure cannot be categorized by applying the Zintl-Klemm concept is the mineral stützite, Ag5−xTe3, that crystallizes in a broad homogeneity range (1.44 ≤ x ≤ −0.25) [125].…”