Investigations on the local structures and spin Hamiltonian parameters for the orthorhombic Rh2+ centers R4 and R5 in AgCl microcrystals

The local structures and spin Hamiltonian parameters (SHPs, g factors, hyperfine structure constants and superhyperfine parameters) are theoretically investigated for the two orthorhombic Rh2+centers R4 and R5 in AgCl microcrystals. Center R4 is ascribed to the impurity Rh2+substituted for Ag+ with two H2O molecules substituted for the nearest neighbor ligands Cl− along the [100] and [010] axes, each with one next nearest neighbor Ag+ vacancy (VAg) due to charge compensation. The impurity Rh2+is found to experience a small off-center displacement 0.006 Å along the [1¯1¯0] axis because of the electrostatic interactions of the substitutes and the VAg. Center R5 is attributed to the impurity Rh2+substituted for Ag+ associated with one H2O molecule substituted for the nearest neighbor ligand Cl− along the [100] axis and one next nearest VAg along the [010] axis. Due to the effective positive charge of the substitute, Rh2+ is repulsed away from the substitute by about 0.008 Å along the [1¯00] axis, while the intervening ligand Cl− in Rh2+and VAg suffers a small inward displacement 0.010 Å towards the center of octahedron. The calculated SHPs based on the above local structures show good agreement with the experimental data for both centers.