Crystal structure and magnetic properties of Li1-xNaxFePO4 based on Mössbauer spectroscopy

The Na-doped Li1-xNaxFePO4 (x = 0.0, 0.01, 0.05, 0.1, 1) samples were synthesized by solid-state reaction method and investigated with X-ray diffractometer (XRD), vibrating sample magnetometer (VSM) and Mössbauer spectrometer. Based on XRD patterns, analyzed by the Rietveld refinement method, Li1-xNaxFePO4 samples were determined to have an orthorhombic structure with space group Pnma. From the temperature-dependent magnetization curve, we have determined the Néel temperature (TN) and observed abnormal antiferromagnetic behavior. Below TN, the Mössbauer spectra appeared to have asymmetrical line-shapes and were analyzed with one set of eight absorption lines. The Mössbauer spectra also showed the Néel temperature (TN) as well as the abnormal antiferromagnetic behavior as in the temperature-dependent magnetization curve. The abnormal antiferromagnetic behavior is expected to be originated from the spin reorientation and the corresponding spin reorientation temperature (TS) is determined experimentally.