Structure and Magnetic Properties of Impurity Complexes [NiF4F4Fint]6(C4v) in the BaF2 Crystal: EPR Study Data

Impurity paramagnetic complexes [NiF4F4Fint]6–(C4v), stable associates of the trivalent nickel ion with the interstitial fluorine ion $${\text{F}}_{{{\text{int}}}}^{-}$$ , were synthesized in BaF2 ionic crystals with the fluorite structure. The molecular structure of the synthesized complexes was studied by electron paramagnetic resonance at frequencies of 9.39 and 34.25 GHz in the temperature range from 5 to 250 K. It was shown that, in the studied complex, the Ni3+ ion (3d7, 4F, S = 3/2) replaces the lattice cation Ba2+ but, under the influence of $${\text{F}}_{{{\text{int}}}}^{-}$$ in the neighboring interstice of the octahedral type, is shifted toward it from the center of the coordination cube occupied by it. Under the influence of the crystal field of tetragonal symmetry, the electron spin levels of the complex are split into two Kramers doublets, of which the ground state Kramers doublet turned out to be $$\left| { \pm 1.2} \right\rangle $$ . The energy interval between doublets is approximately 114 GHz. The EPR spectra exhibit a superhyperfine structure caused by the interactions of the electron spin moment of the nickel ion with the nuclei of nine ligand fluorine ions. The parameters of these interactions were determined.