Real and Hypothetical Intermediate-Valence AgII/AgIII and AgII/AgI Fluoride Systems as Potential Superconductors

摘要: With the aim of gauging their potential as conducting or superconducting materials, we examine crystal structures and magnetic properties roughly one hundred binary, ternary, quaternary Ag(II) Ag(III) fluorides in solid state reported up to date. The cation appears these species usually a distorted octahedral environment, either an [AgF](+) infinite chain [AgF(2)] sheets. Sometimes finds discrete square-planar [AgF(4)](2-) ions. occurs form isolated [AgF(4)](-) Systems containing (d(8)) centers are typically diamagnetic. On other hand, rich spectrum (d(9)) environments binary ternary leads most diverse properties, ranging from paramagnetism, through temperature-independent paramagnetism (characteristic for half-filled band metallic behavior) antiferromagnetism, weak ferromagnetism. have same d-electron count Cu(II) Cu(III) (d(8)), respectively. F(-) O(2-) ions isoelectronic, closed-shell (s(2)p(6)) species; both weak-field ligands. Led by similarities, some experimental evidence, analogies between cuprates (Cu(II)/Cu(III)-O(2-) Cu(II)/Cu(I)-O(2-) systems) formally mixed-valence Ag(II)/Ag(III)-F(-) Ag(II)/Ag(I)-F(-) phases. For this purpose perform electronic-structure computations number structurally characterized Ag(I), Ag(II), compare results with similar calculations oxocuprate superconductors. Electronic levels vicinity Fermi level (x(2)-y(2) z(2)) strongly mixed Ag(d)/F(p) character Ag-F antibonding, thus providing efficient vibronic coupling (typical d(9) systems substantially covalent bonds). According our is result not only coincidence orbital energies; surprisingly bonding fluorides. electron density at (DOS(F)) silver fluoride materials frequencies metal-ligand stretching modes values close those copper oxides. above features suggest that properly hole- electron-doped might be good BCS-type We analyze comproportionation/disproportionation equilibrium hole-doped fluorides, possible appearance holes F(p) band. It seems there chance generating Ag(III)-F(-)/Ag(II)-F(0) "ionic/covalent" curve crossing Ag(II)-F(-) significantly increasing coupling.