57Fe and 119Sn Mössbauer, XRD, FTIR and DC conductivity study of Li2OFe2O3SnO2P2O5 glass and glass ceramics

Glass samples with a composition of 1.5Li2O
- (1.5-x)Fe2O3
- xSnO2
- 3P2O5 (x = 0.1, 0.3 and 0.5) were prepared by melt-quench method. X-ray diffraction (XRD) study revealed the glass formation of the as-quenched samples. Each glass sample was heat treated (HT) at 600 °C for 1 h to obtain glass ceramics. HT samples showed precipitation of a small amount of crystalline particles assigned to LiFeP2O7. Local structure of these samples was explored by means of Fourier transform infrared spectroscopy and Mössbauer spectroscopy. They proved that Fe3+ ions occupied the sites of network former, while Fe2+ and Sn4+ the sites of network modifier. DC conductivity (σ) measurement of these samples showed non-linear temperature dependency. Activation energy showed a slight decrease with an increasing amount of SnO2, and the σ measured at 500 K increased from 5.6 × 10−5 to 3.9 × 10−4 S cm−1. The σ values of HT samples were one-order of magnitude larger than those of the corresponded as-quenched glass samples, reflecting structural relaxation of the 3D-network composed of distorted FeO4 and PO4 tetrahedra. The approximated ratio of electronic-to ionic-conduction, σelec/σion, suggested that the conduction became predominantly “ionic” at high temperatures. The present study will be useful for the development of new cathode active material and solid state electrolyte for lithium ion battery.