Unexpected Coexisting Solid Solutions in the Quasi-Binary Ag (II) F 2 /Cu (II) F 2 Phase Diagram

• Published in: Chemistry : a European journal Vol. 29; no. 52; p. e202301092
• Main Authors: Jezierski, D, Koteras, K, Domański, M, Połczyński, P, Mazej, Z, Lorenzana, J, Grochala, W
• Format: Journal Article
• Language: English
• Published: Germany 15-09-2023
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202301092

High-temperature solid-state reaction between orthorhombic AgF
and monoclinic CuF
(y=0.15, 0.3, 0.4, 0.5) in a fluorine atmosphere resulted in coexisting solid solutions of Cu-poor orthorhombic and Cu-rich monoclinic phases with stoichiometry Ag
Cu
F
. Based on X-ray powder diffraction analyses, the mutual solubility in the orthorhombic phase (AgF
 : Cu) appears to be at an upper limit of Cu concentration of 30 mol % (Ag
Cu
F
), while the monoclinic phase (CuF
 : Ag) can form a nearly stoichiometric Cu : Ag=1 : 1 solid solution (Cu
Ag
F
), preserving the CuF
crystal structure. Experimental data and DFT calculations showed that AgF
 : Cu and CuF
 : Ag solid solutions deviate from the classical Vegard's law. Magnetic measurements of Ag
Cu
F
showed that the Néel temperature (T
) decreases with increasing Cu content in both phases. Likewise, theoretical DFT+U calculations for Ag
Cu
F
showed that the progressive substitution of Ag by Cu decreases the magnetic interaction strength |J
| in both structures. Electrical conductivity measurements of Ag
Cu
F
showed a modest increase in specific ionic conductivity (3.71 ⋅ 10
±2.6 ⋅ 10
 S/cm) as compared to pure AgF
(1.85 ⋅ 10
1.2 ⋅ 10
 S/cm), indicating the formation of a vacancy- or F adatom-free metal difluoride sample.