Polymorphism of Fluoroargentates(II): Facile Collapse of a Layered Network of α-K2AgF4 Due to the Insufficient Size of the Potassium Cation

Dominik Kurzydłowski, Marianna Derzsi, Armand Budzianowski, Zvonko Jagličić, Wiktor Koźmiński, Zoran Mazej, Wojciech Grochala

European Journal of Inorganic Chemistry
Volume 2010, Issue 19, pages 2919–2925, July 2010
DOI: 10.1002/ejic.201000124

Dediacted to the memory of Neil Bartlett

Abstract

We report the crystal structure and magnetic properties of a novel β polymorph of K2AgF4. β-K2AgF4 is paramagnetic above 20 K and exhibits a low Curie temperature (θ < 5 K). Solid state DFT (GGA and GGA+U) calculations were performed to analyze the electronic and magnetic structure of β-K2AgF4 at 0 K/0 GPa, reproducing correctly the ferromagnetic (FM) semiconductor ground state with the band gap at the Fermi level of approximately 1.65eV. Furthermore, we show that the novel β form is thermodynamically favoured over the previously reported two-dimensional α form and can be formed either by slow spontaneous exothermic α to β phase transition occurring on heating or direct synthesis from KF and AgF2 at 300°C. The relative stability of the α and β phases is rationalized in terms of the size of the M+cation in the M2M′F4 series (M = Na, K, Cs, M′ = Cu, Ag) and the mismatch between [MF] and [M′F4/2] sublattices in the layered perovskite α form.

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