Defect structure and spin-Hamiltonian parameters for the CuCl 64− cluster in the tetragonal RbCdCl 3:Cu 2+ crystal

Abstract

The tetragonal distortion (characterized by R ∥ − R ⊥ where R ∥ and R ⊥ 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 ∥, g ⊥ and hyperfine structure constants A ∥, A ⊥). The calculations are performed by using the complete high-order perturbation formulas for 3 d 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 ∥ − R ⊥ ≈ 0.14 Å 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 = Δ g i or A i ( 2 ) , i = ∥ or ⊥) are about 12% and 9% for Q = Δ g 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.