Controlling orbital ordering of intergrowth structures with flat [Ag(II)F2] layers to mimic oxocuprates(ii)

Abstract

Based on density functional theory calculations, we propose a new pathway toward compounds featuring flat [AgF₂] layers which mimic [CuO₂] layers in high-temperature oxocuprate superconductor precursors. Calculations predict the dynamic (phonon) and energetic stability of the new phases over diverse substrates. For some compounds with ferro orbital ordering, we find a gigantic intrasheet superexchange constant of up to −211 meV (DFT+U) and −256 meV (SCAN), calculated for hypothetical (CsMgF₃)₂KAgF₃ intergrowth. Semiempirical calculations show that at optimum doping, the expected superconducting critical temperature should reach 200 K. The partial substitution of K⁺ with Ba²⁺ leads to noticeable electron doping of the [AgF₂] sublattice, as revealed by progressive population of the upper-Hubbard band. On the other hand, modest 10–15% hole-doping through partial substitution of Mg²⁺ with Li⁺, primarily leads to the depopulation of p_(z) orbitals of apical F atoms. We also find structures with an undesired antiferrodistortive structural ordering and discuss the structural factors that determine the transition from buckled to flat planes and from different types of orbital ordering using the Landau theory of phase transitions.