Superhyperfine interaction in the trigonal center BaF2: Gd3+ and the lattice distortion analysis in the vicinity of the impurity ion

The constants of the superhyperfine interaction of Gd³⁺ with the ¹⁹F nuclear spins in the first four coordination shells were determined from the ENDOR spectra of a trigonal BaF₂: Gd³⁺ center. These data were used for analysis of the crystalline lattice distortions in the vicinity of the impurity ion. It was found that the largest displacements of fluorine nuclei occurred in the vicinity of the ion compensator and the impurity ion. To calculate the anion positions within the first coordinate shell, whose electron-nuclear interaction with Gd³⁺ depends considerably on chemical bonds in the Gd³⁺F ₈ ^? complex, an empirical model is used for the isotropic constants of the superhyperfine interaction of Gd³⁺ with fluorine nuclei in cubic centers, with allowance made for the impurity ion polarization.