EPR Investigations on the (FeOF₅)⁴⁻ Cluster in KZnF₃

Abstract

The X band EPR spectrum of the (FeOF,)4-cluster in KZnF, single crystals was analysed. We used a computer diagonalization for both the Zeeman interaction and the axial crystal field term and a perturbation treatment for the cubic field term and for the shf interaction. This cluster appears to be well adapted for EPR investigations of the structural properties of fluoperovskites.Nous avons 6tudi6 en bande X le spectre RPE du complexe (FeOF,J4-dans des monocristaux de KZnF,. La d6termination des parametres de I'Hamiltonien a 6t6 effectde, soit par diagonalisation des matrices pour l'effet Zeeman et le terme de champ axial, soit par un traitement des perturbation pour le terme de champ cubique et l'interaction superhyperfine. Ce complexe apparait comme bien adapt6 aux 6tudes par R P E des propribt6s structurales des fluopbrovskites.

A complex defect studied through DFT: The Fe3–O2− pair in KMgF3

“…With the exception of this case, where f s (eq)/f s (ax) = 3.5, the other results collected in Table II lead to values of f s (eq)/f s (ax) lying between 1.8 and 2.1. These figures are thus close to the A s (eq)/A s (ax) values 5, 8–11 measured for FeF 5 O 4− in KMgF 3 (2.4), KZnF 3 (1.8), and RbCdF 3 (2.0).…”

“…In the case of a trivalent impurity, M, in fluoroperovskites EPR and ENDOR spectra have shown a strongly axial signal that was assumed to be due to a MF 5 Y center with C 4V symmetry (Fig. 1), involving a compensating anion Y, which replaces a fluorine ligand 8–13. This Y anion does not give rise to superhyperfine structure.…”

“…This kind of center has also been formed for M being Fe 3+ , Gd 3+ , or Yb 3+ . Because its formation is enhanced by introducing the impurity through the corresponding oxide 9, 11–13, the nature of Y has been assumed to be O 2− . Moreover, because 16 O has zero nuclear spin and the natural abundance of 17 O is only about 0.04%, this fact is consistent with the absence of superhyperfine interaction coming from the Y ligand in EPR and ENDOR spectra.…”

“…For definite clarification of the structure of this center it is necessary to first account for the only available experimental data obtained by means of EPR and ENDOR techniques. So, all centers ascribed to FeF 5 O 4− units in lattices such as KMgF 3 5, 8, KZnF 3 , or RbCdF 3 5, 9–11 exhibit an isotropic superhyperfine constant corresponding to the four equatorial fluorines (A s (eq)), which is about twice that coming from the apical fluorine (A s (ax)). Searching to clarify the structure of the center in KMgF 3 , DFT calculations have been carried out, considering the good results obtained on cubic centers of Fe 3+ and Mn 2+ impurities in fluoroperovskites 4, 6.…”

Theoretical investigation of local lattice structure of the tetragonal FeF5O cluster in KMgF3:Fe3+ crystal

“…In the last years much attention has been paid to the investigations of transition-metal (TM) ions doped into fluoroperovskite-type AMF 3 crystals (A represents an alkali metal and M represents an alkaline-earth metal ion) [1][2][3][4][5][6][7][8][9][10]. Magnetic impurity ions doped in the layered perovskite fluorides are expected to substitute for host cations and form the magnetic impurity center.…”