Geometrical information from electronic properties: application to 3d impurities

A better insight into the properties due to an impurity in an insulating lattice requires the knowledge of the actual impurity-ligand distance R. To solve this important problem, a study of the R dependence of spectroscopic parameters can be of great help. In the present work the R dependence of the crystal-field parameter, 10 Dq, and the isotropic superhyperfine constant, A(s), for Fe complexes embedded in fluorides is firstly explored. It is concluded that R variations (induced by a hydrostatic pressure) down to 0.04 pm can be detected through A(s) measured by ENDOR. Attention has to be paid, however. when two different kinds of lattices containing the same complex are to be compared. Although the core polarization contribution to the isotropic hyperfine constant, A, is found to be slightly dependent on R a different situation can occur when the 3d-4s hybridization is allowed. In MX6 complexes (M:d(9) ion: X:ligand) displaying a compressed geometry it is found that A becomes extremely sensitive to changes of axial and equatorial metal-ligand distances. Experimental results on BaZnF4:Cu, K2ZnF4:Cu and CuCl4(NH3)(2)(2-) complexes in NH4Cl support this conclusion. (C) 2001 Elsevier Science B.V. All rights reserved.