Mapping of second-nearest-neighbor fluoride ions of orthorhombic Gd 3+-Ag + complexes in CaF 2

Abstract

The ENDOR technique is applied to determine the positions of 24 second-nearest-neighbor F − ions around an orthorhombic Gd 3+-Ag + complex in CaF 2 crystals. Experimental ENDOR data of the second-nearest-neighbor F − ions are analyzed by using the usual spin Hamiltonian and a least-squares fitting method. The best fits of the experimental results give superhyperfine (shf) constants and the F − directions ( K, L, M) with respect to the Gd 3+ ion, from which the distance between the second-nearest-neighbor F − ion and the Gd 3+ ion is determined by assuming that the hyperfine interaction is due to the classical dipole-dipole interaction. The displacements of the F − ions are estimated and compared with the theoretical values calculated by Bijvank and den Hartog on the basis of a polarizable point charge model.