Studies of the local structures and spin Hamiltonian parameters for the two Rh2+ centers in AgBr

The local structures and the spin Hamiltonian parameters (the g-factors g(parallel to) and g(perpendicular to) and the superhyperfine parameters A(parallel to)' and A(perpendicular to)') are quantitatively studied for the two Rh2+ L and H centers (denoting the tetragonally elongated and compressed [RhBr6](4-) clusters at low and high temperatures, respectively) in AgBr using the perturbation formulas of these parameters for a 4d(7) ion in tetragonally elongated and compressed octahedra. From the studies, the elongated L center originates from the relative elongation of the parallel Rh2+-Br- bonds by about 0.081 angstrom along the C-4 axis because of the Jahn-Teller effect. Nevertheless, the compressed center H is attributed to one next nearest neighbouring Ag+ vacancy V-Ag along the C-4 axis as the charge compensator, which compels the intervening ligand Br- in the Rh2+ and the V-Ag to shift away from the latter by about 0.148 angstrom because of the electrostatic repulsion. All the calculated spin Hamiltonian parameters based on the above local structures are in good agreement with the experimental data for both centers.