Crystal Structure Imperfection of LiFePO4 Synthesized Through Solid-state Reaction: An XRD Overview

Solid-state reaction is one of some methods to synthesize LiFePO4 powder. However, the post-synthesis crystal structure was found to be imperfect, probably caused by the imperfection of the phospho-olivine structure. This study aimed to investigate the cause of its imperfection. A LiFePO4 powder synthesized via solid-state reaction path was used as a case study sample for this study. XRD characterization was done to investigate it. Orthorhombic crystal structure was found to be a perfect fit for this sample using precise lattice parameter analysis, as shown by the linear regression equation result. Further analysis was performed using Rietveld refinement method to pinpoint the actual coordinates of Li, Fe, P, and O atoms. The result shows that solid-state reaction can produce an order of orthorhombic crystal structure which constructed by ordered Li atoms arrangement. On the other hands, there is a disordered phospho-olivine structure due to the imperfection of the occupation of Fe, P, and O atoms. These disorders were found through analysis of anomalous peaks on the Rietveld refinement result when compared with PDF database. Loss of (200) plane was caused by imperfect occupation of O atoms, while imperfect occupation of Fe and P atoms leads to new (200) plane of FeP4 phase which has a monoclinic crystal structure.