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Common polymorph of silver difluoride (AgF2) at ambient pressure has layered antiferromagnetic structure. The phase exhibits numerous structural and electronic similarities with oxocuprate precursors of high-temperature superconductors. The 2D antiferromagnetically (AFM) ordered sheets along with large super-exchange constant possess the same topology as [CuO2] layers in the high-temperature superconducting oxocuprates. X-ray diffraction (XRD) study of phase transitions at high pressure and Density functional theory modeling (DFT) [1] showed that at an elevated pressure of 15 GPa, AgF2 transforms to an unprecedented orthorhombic high-pressure polymorph (HP2) featuring an array of tubular subunits, which are built of corner sharing [AgF4] squares. This features the first 1D-type of a metal fluoride nanowire, which is the only one showing rigid square planar rather than common hexagonal or octahedral moieties. The tubular subunits are densely packed in the crystal lattice with AFM ordering. DFT simulations supported by XRD measurements also suggested that HP2 tubular polymorph of AgF2 can exhibit dynamic lattice stability in the broad pressure range from ambient up to 80 GPa [2]. Due to the presence of the half-spin Ag(II) cations, the 1D-AgF2 could have an interesting magnonics. The fact that the individual AgF2 nanowire units are neutral and held together only by van der Waals interactions suggests that they could be in principle isolated from the crystal. In this respect we focused on first-principles investigation of the mechanical stability, elasticity and response of electronic structure and lattice dynamics to applied uniaxial strain to isolated 1D-AgF2 subunit structure. The mechanical properties and lattice dynamics in the AgF2-nanowire were predicted and analysed by use DFT+U functionals and quasi-harmonic approximation.
[1] A. Grzelak et al., Inorg. Chem., 56, 14651−14661 (2017).
[2] A. Grzelak et al., Dalton Trans., 46, 14742 (2017).
| Speaker Country | Slovakia |
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