Defect structure and spin-Hamiltonian parameters for the CuCl(6)(4-) cluster in the tetragonal RbCdCl(3):Cu(2+) crystal.

The tetragonal distortion (characterized by R( parallel)-R( perpendicular) where R( parallel) and R( perpendicular) denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis, respectively) for CuCl(6)(4-) cluster in the tetragonal RbCdCl(3):Cu(2+) crystal is studied by calculating its spin-Hamiltonian (SH) parameters (g factors g( parallel), g( perpendicular) and hyperfine structure constants A( parallel), A( perpendicular)). The calculations are performed by using the complete high-order perturbation formulas for 3d(9) ions in tetragonal symmetry based on a two-mechanism model, in which both the widely-used crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (which is omitted in CF theory) are considered. From the calculations, the SH parameters are reasonably explained and the tetragonal distortion R( parallel)-R( perpendicular) approximately 0.14A is obtained. The distortion is much larger than those caused by the cubic-tetragonal transition phase, but is in the same order as those found in many similar CuCl(6)(4-) Jahn-Teller systems. So, the tetragonal distortion (or defect structure) for the CuCl(6)(4-) cluster in RbCdCl(3):Cu(2+) is due mainly to the Jahn-Teller effect. The relative importance of CT mechanism (characterized by Q(CT)/Q(CF), where Q=Deltag(i) or A(i)((2)), i= || or perpendicular are about 12% and 9% for Q=Deltag(i) and A(i)((2)), respectively. It appears that for the exact calculations of SH parameters of CuCl(6)(4-) clusters in crystals, the contributions due to both CF and CT mechanisms should be taken into account.