Investigation of Microscopic Crystal Field in Co-Doped Lithium-Iron Phosphate

We present the study on the structural and the magnetic properties of LiFePO₄ and LiFe_0.8Co_0.2PO₄. The crystal structure was determined to be orthorhombic with space group Pnma by Rietveld refinement method. We have observed the increase in the lattice constants with Co²⁺ ion substituted. The Mossbauer spectra of olivine LiFePO₄ and LiFe_0.8Co_0.2PO₄ have shown distorted line broadening below T _N . In order to explain the observed line broadening, we have analyzed the Mossbauer spectra by considering the full Hamiltonian for the ⁵⁷Fe nucleus, and both the magnetic dipole and the electric quadrupole interactions. Also, we have observed the anomalous change in the electric quadrupole splitting near the T _N.