Synthesis and Li+ ion conductivity of Li2O–Nb2O5–P2O5 glasses and glass–ceramics

Glasses with the compositions of xLi2O–(70 − x)Nb2O5–30P2O5, x = 30–60, and their glass–ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li+ ion conductivities of glasses and glass–ceramics are examined to clarify whether the glasses and glass–ceramics prepared have a potential as Li+ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li2O content, and the glass of 60Li2O–10Nb2O5–30P2O5 shows the value of σ = 2.35 × 10−6 S/cm at room temperature and the activation energy (Ea) of 0.48 eV for Li+ ion mobility in the temperature range of 25–200 °C. It is found that two kinds of the crystalline phases of Li3PO4 and NbPO5 are formed in the crystallization of the glasses and the crystallization results in the decrease in Li+ ion conductivity in all samples, indicating that any high Li+ ion conducting crystalline phases have not been formed in the present glasses. 60Li2O–10Nb2O5–30P2O5 glass shows a bulk nanocrystallization (Li3PO4 nanocrystals with a diameter of ∼70 nm) and the glass–ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10−7 S/cm at room temperature and Ea = 0.49 eV.