Studies on the Local Structure and the Spin Hamiltonian Parameters for Co2+ in CaTiO3 |
| Journal |
Defect and Diffusion Forum (Volume 278) |
| Volume |
Defects and Diffusion in Metals |
| Edited by |
David J. Fisher |
| Pages |
55-62 |
| DOI |
10.4028/www.scientific.net/DDF.278.55 |
| Online since |
July, 2008 |
| Authors |
Guang Duo Lu,
Shao Yi Wu,
Hua Ming Zhang,
Li Hua Wei
|
| Keywords |
CaTiO3, Co2+, Defect Structure, Electron Paramagnetic Resonance (EPR) |
| Abstract |
The local structure and the spin Hamiltonian parameters g factors gi (i =x, y and z) and
the hyperfine structure constants Ai for Co2+ in orthorhombic CaTiO3 are theoretically investigated
from diagonalization of 6 × 6 energy matrix within the 4T1 ground state for a 3d7 ion in
orthorhombic symmetry. In the calculations, the contributions from the admixtures of various J
states (J=1/2, 3/2, 5/2), the ligand orbitals and spin-orbit coupling and the fourth-order orthorhombic
field parameter, which were usually neglected in the previous works, are taken into account. The
crystal-field parameters are determined from the superposition model in consideration of the
suitable lattice distortion due to the charge and size mismatching substitution of Ti4+ by Co2+. Based
on the studies, the bond lengths R1 and R2 in the xy plane are estimated to suffer the relative
alternation R ≈ 5.4%, yielding more significant orthorhombic distortion in the impurity center as
compared with that for the host Ti4+ site in pure crystal. The calculation results based on the above
local lattice distortion show reasonable agreement with the observed values. The various
contributions to the spin Hamiltonian parameters are discussed. Present studies may theoretically
verify that the impurity Co2+ occupies the 6-fold coordinated Ti4+ site rather than the 12-fold
coordinated Ca2+ site, associated with the enhanced orthorhombic distortion due to the mismatching
substitution. |
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