EPR theoretical study of local lattice structure of Fe3+ in octahedral site in yttrium gallium garnet

By analyzing the EPR parameters D and (a-F) of Fe3+ ion located at octahedral site in yttrium gallium garnet, the local lattice structure around Fe3+ ion in the crystal has been investigated on the basis of the complete energy matrices for a d5 configuration ion in a trigonal ligand field. It is shown that there exists a slight expansion distortion in the local lattice structure and the distortion is different at 4.2 and 295K. This result may be attributed to the fact that the radius of Fe3+ ion is larger than that of Ga3+ ion, and the Fe3+ ion will push the two oxygen triangles to move upwards and downwards, respectively, along C3-axis when the temperature decreases. From EPR calculation, the local lattice structure parameters R=2.0068A, θ=51.4691 deg. at 295K and R=2.010A, θ=51.3706 deg. at 4.2K for octahedral Fe3+ centre in yttrium gallium garnet are determined