Effect of Ba:Ti on ferroelectric properties of LiF doped BaTiO₃ ceramics

We prepare three different LiF doped BaTiO₃ ceramics by solid state reaction, i.e., (i) the Ba_1−xLi_xTiO_3−xF_x ceramics (abbreviated as BLiFT-x), (ii) the BaTi_1−xLi_xO_3−2xF_x ceramics (abbreviated as BTLiF-x), and (iii) the xLiF + BaTiO₃ mixed ceramics (abbreviated as LiFBT-x). Through XRD analysis and electrical properties comparison, it is concluded that Li⁺ ions occupy Ba site and F⁻ ions occupy O site in BLiFT-x and LiFBT-x ceramics, but the solubility of Li⁺ and F⁻ ions are small and most of them occupy the interstitial site. Thus there are two peaks near Curie point. The d₃₃ and k_p increase firstly and then decrease with the increase of LiF content. However, Li⁺ ions occupy Ti site in BTLiF-x ceramics. The [Li_Ti-F_O]²⁻ defect dipoles are formed, which have a pinning effect and appear thin waist hysteresis loops. The d₃₃ and k_p decrease with the increase of LiF content. For all three group of ceramics, the Curie temperature decreases while the dielectric constant increases with the increase of LiF content. Compared Li₂CO₃ doped BaTiO₃ (Ba/Ti < 1, Ba/Ti > 1 and Ba/Ti = 1) ceramics with LiF doped BaTiO₃ (Ba/Ti < 1, Ba/Ti > 1 and Ba/Ti = 1) ceramics, the positions of Li⁺ ions occupying BaTiO₃ are different with Li₂CO₃ doped BaTiO₃ ceramics due to F⁻ ions entering BaTiO₃ in LiF doped BaTiO₃ ceramics, which affect the structure, morphology and properties of BaTiO₃ ceramic. This will provide some guidances to choose sintering additives and prepare methods for low temperature sintering in the future.