Effect of alkaline excess on sintering, microstructural, and electrical properties of Li0.12Na0.88NbO3 ceramics

Abstract

Sintering behavior in Li0.12Na0.88NbO3 (LNN-12) ceramics has been investigated by analyzing the microstructures of the samples sintered at different temperatures (1050–1250 °C) and durations (1–6 h) to optimize the sintering conditions. An excess amount of Li2CO3 was added (1, 3, 5 mol%) to stoichiometric LNN-12 in order to compensate for the probable alkaline element loss at higher optimized sintering temperature. The addition of excess Li2CO3 into the starting materials and the effect of it on microstructure and electrical properties were investigated. Microstructural study of Li2CO3-added samples revealed abnormal grain growth, a characteristic feature of liquid phase sintering due to the low melting Li2CO3. The temperature and frequency dependence of dielectric constant shows two phase transitions in temperature dependence and low-frequency dispersion in the frequency dependence of dielectric plot. The observed frequency dispersion is attributed to dominant DC conductivity. The conduction mechanism was identified as diffusion of intrinsic Li+ ion. The room-temperature dielectric constant and loss factor were found to increase with increase in Li2CO3 addition from 160 to 690 and 0.02 to 0.04, respectively. The electrical conductivity was found to increase two orders of magnitude (10−12–10−10 Ω−1 cm−1) in Li2CO3-added samples as compared to stoichiometric composition. The results obtained here give a strong evidence of the stoichiometry–microstructure and electrical properties correlation, thus emphasizing on the importance of processing parameters to tune the desired properties in Li0.12Na0.88NbO3 ceramics.