EFFECT OF Li2WO4 AND Li3PO4 ADDITION ON THE SINTERING TEMPERATURE AND DIELECTRIC PROPERTIES OF BaTiO3-BASED CERAMICS

Abstract

The growing demand for multi-layer ceramic capacitor (MLCCs) in electronic industry has attracted immense research interest due their high capacitance, small size, reliability and excellent high frequency characteristics. Furthermore, a decrease in the sintering temperature of BaTiO3 (BT) based compounds without too much compromise on the dielectric properties is technologically important in the fabrication of MLCCs. The objective of the present study was to investigate the effect of Li3PO4 and Li2WO4 addition on the sintering temperature and dielectric properties of BT-based ceramics for their possible applications in MLCCs. A number of compositions in the (1-x)BaTiO3–xLi3PO4 (x = 0, 0.01, 0.03, 0.05, 0.10) and (1-x)BaTiO3–xLi2WO4 (x = 0, 0.01, 0.05, 0.10) series were prepared via a solid state reaction route and characterized in terms of phase purity, microstructure and electrical properties. Both the additives were found effective in lowering the sintering temperature of BT from ~1350 ºC to ~1150 ºC. X-ray diffraction analysis revealed the formation of tetragonal BT along with BaLiPO4 at x = 0.01-0.05 and another additional secondary LiPO3 phase at x = 0.10 in the case of (1-x)BaTiO3–xLi3PO4. The Li2WO4 added BT samples revealed the formation of tetragonal BT with an additional phase BaWO4 at x = 0.01-0.10. The dielectric constant for Li3PO4 added samples decreased from ~4288 to ~3600, remnant polarization from 6.70 μC/cm2 to 3 μC/cm2 and coercive field from 3.32 kV/cm to 2.5 kV/cm with an increase in x from 0 to 0.05. In the case of Li2WO4 added samples, the dielectric constant decreased from ~4288 to ~1064. The Curie temperature (Tc) peak of Li2WO4 added samples became more diffused and shifted towards room temperature with an increase in x from 0 to 0.10. The IV remnant polarization of Li2WO4 added samples decreased from ~6.70 μC/cm2 to ~2 μC/cm2 while the coercive field increased from ~3.32 kV/cm to ~7.5 kV/cm, when x was increased from 0 to 0.10. Moreover, for the (1-x)BaTiO3–xLi3PO4 (x = 0, 0.01, 0.03, 0.05, 0.10) compositions, the bulk and grain boundary conductivities decreased as x was increased to 0.05, possibly due to a decrease in the grain size. While the activation energy of the grain boundary increased with an increase in x from 0.01 to 0.05 as a consequence of an increase in grain boundary area. Upon further increase in x to 0.10, the observed decrease in the activation energy (grain boundary) indicated a decrease in the concentration of grain boundaries and an increase in grain size of the secondary phases, for x = 0.10. The bulk and grain boundary conductivities of (1-x)BaTiO3–xLi2WO4 compositions also decreased with increasing x. The activation energy for the bulk decreased due to Li2WO4 addition (x = 0.01) and then increased upon further increase in the concentration of Li2WO4 (up to x = 0.05). On the other hand, activation energy for the grain boundary, initially increased with the addition of Li2WO4 (at x = 0.01) and decreased upon further increase in the concentration of the additive to x = 0.10. This may be due to the consequent increase in the concentration of the secondary phase (BaWO4) as well as a small increase in the grain size. These two electro-active regions (i.e., grain and grain boundary) having different thermal activation energies suggested two different transport mechanisms in the (1-x)BaTiO3–xLi2WO4 (where x = 0, 0.01, 0.05, and 0.10) ceramics investigated in the present study. V In conclusion, these results suggest that Li3PO4 and Li2WO4 were effective in lowering the sintering temperature for BT–based ceramics and may be considered as potential candidate materials for the fabrication of MLCCs.