How do electrons travel in unusual metallic fluorides of Ag²⁺?

Abstract

We investigate computationally two representative examples of higher fluorides of Ag(II), namely KAgF3 and AgFBF4. Both compounds formally contain linear (Ag-F) + chains, in which divalent silver is coordinated additionally by four fluoride anions. For AgFBF4, the equatorial coordination is weak, and leads to metallic conductivity in 1D, as emerges from our band structure calculations. For KAgF3, however, the axial coordination is very strong, and the compound is virtually a 2D metal (i.e. it is mainly the x 2 -y 2 orbitals of Ag that participate in electronic transport in this interesting material).

Pressure-induced transformations of AgIIF2—towards an ‘infinite layer’ d9material

“…Since neither d(z 2 ) Ag nor the p(z) F orbitals contribute to the bands crossing the Fermi level, we may anticipate that δ-AgF 2 is-structurally and electronically-a 2D material. This feature sets δ-AgF 2 apart from other compounds with the [AgF 2 ] sheets, but with the compressed O h coordination of Ag 2+ [26], and makes it similar to infinite layer oxocuprate superconductors [27]. Notably, δ-AgF 2 , if experimentally preparable, would be the first example of a layered (polymeric) fluoride of Ag 2+ with flat [AgF 2 ] sheets and short intra-sheet Ag-F distances [28] 14 .…”

Origin of ferromagnetism inCs2AgF4: The importance ofAg−Fcovalency

“…Moreover, related compounds have been shown both in band structure calculations and x-ray photoelectron spectroscopy experiments to display significant Ag-F covalency, reminiscent of the Cu-O hybridization in the cuprates. 2,6,7 These similarities and other considerations have led to speculations about possible high temperature superconductivity in Ag͑II͒ fluorides. 2,8 One puzzling difference between the cuprates and the layered Ag͑II͒ fluorides is that the undoped cuprates are antiferromagnetic, while the argentates are ferromagnetic.…”

“…This hybridization involves both F1 and F2 atoms, and is consistent with previous results for Ag(II) fluorides. 2,6,7 The result is a very stable metallic electronic structure, with substantial F character at the Fermi energy, E F , and a valence band width of ∼ 5.5 eV. This strong hybridization can be understood in chemical terms considering the very strongly oxidizing character of Ag(II), which in this compound partially oxidizes F − .…”

Crystal, electronic, and magnetic structures of M2AgF4 (M = Na–Cs) phases as viewed from the DFT+U method

“…11 Nearly four decades later, our experimental investigations [12][13][14] have indicated that M 2 AgF 4 connections can adopt two structure types: the layered perovskite structure and the post-perovskite Na 2 CuF 4 -type phase. These studies, together with other experimental [15][16][17][18] and theoretical [19][20][21][22][23][24] investigations led to a better understanding of the complex magnetic and electronic structures of these charge-transfer insulators; however, some unresolved issues still remain. The first one is the rationalization of the structural trends observed in the M 2 AgF 4 series, i.e., the change of the ground state structure from the layered perovskite to the post-perovskite polymorph, when gradually moving from Cs 2 AgF 4 to Na 2 AgF 4 .…”