Site occupancy of divalent cobalt in fluorides : a powder ESR study

The preferential site occupancy of Co super(2+) is investigated through electron spin resonance (ESR) in various powdered fluorides hosts in which the possible coordination number for divalent cations, CN, can vary from 4 to 12. In the case of CN4 and CN8 the spectrum is typical of an effective spin S ) 3/2 ground-state (g ) 2.3) with a rather important zero-field splitting in the case of tetrahedral sites. For other coordination polyhedra the g-tensor values, ranging from 8 to 1, arise from the lowest lying doublet of the super(4)F multiplet (effective spin S ) 1/2) as in CN6. They can reflect the site occupancy and symmetry as demonstrated by the experimental and simulated powder ESR spectra.