Study of spin-phonon coupling in LiFe1-xMnxPO4 olivines

Abstract

LiFe(1-x)MnxPO(4) olivines are promising material for improved performance of Li-ion batteries. Spin-phonon coupling of LiFe(1-x)MnxPO(4) (x = 0, 0.3, 0.5) olivines is studied through temperature-dependent Raman spectroscopy. Among the observed phonon modes, the external mode at similar to 263 cm(-1) is directly correlated with the motions of magnetic Fe2+/Mn2+ ions. This mode displays anomalous temperature-dependent behavior near the Neel temperature, indicating a coupling of this mode with spin ordering. As Mn doping increases, the anomalous behavior becomes clearly weaker, indicating the spin-phonon coupling quickly decreases. Our analyses show that the quick decrease of spin-phonon coupling is due to decrease of the strength of spin-phonon coupling, but not change of spin-ordering feature with Mn doping. Importantly, we suggest that the low electrochemical activity of LiMnPO4 is correlated with the weak spin-phonon coupling strength, but not with the weak ferromagnetic ground state. Our work would play an important role as a guide in improving the performances of future Li-ion batteries. Copyright (C) 2015 John Wiley & Sons, Ltd.