Effect Of Lanthanide Oxide Additives On Structure And Electrical Properties Of (Na_0.5Bi_0.5)_1-xBa_xTiO₃ Ceramic With A Composition Near MPB

Recently, there is a growing interest of investigating lead-free piezoelectric materials as a possible alternative to widely used lead zirconate titanate (PZT) based ceramics. Sodium bismuth titanate, (Na_0.5Bi_0.5)TiO₃ (NBT) is considered to be one of promising candidates for lead-free piezoelectric ceramics due to a large remanent polarization (P_r=38μC/cm²) at room temperature and a high Curie temperature (T_c=320℃). In this research, a citrate method has been employed to prepare (Na_0.5Bi_0.5)_1-xBa_xTiO₃(abbreviated as NBT-(x)BT) ceramics, and the effect of lanthanide oxide additives on the structure and electrical properties of ceramic with a composition near the rhombohedral-tetragonal morphotropic phase boundary (MPB) have been investigated. The dielectric relaxation feature and the phase transition behavior have been examined with respect to temperature and measuring frequency. The main contributing factors to the ferroelectric and piezoelectric properties of the ceramics have been established based on experimental results.NBT-(x)BT ceramics has been synthesised and prepared by the citrate method. The structural characteristics and electrical properties of NBT-(x)BT ceramics were examined. It was found that the citrate method demonstrates advantages of producing fine and homogeneous powders together with substantially improving the ferroelectric and piezoelectric properties of the resulting ceramics. The analysis of the crystal structure reveals that the MPB of the ceramics lies in the composition range of 0.06 < x <0.10 at room temperature. The piezoelectric and ferroelectric properties of NBT-(x)BT compositions near MPB are rather sensitive to the proportion of rhombohedral and tetragonal phases and reach preferred values at x=0.07, where the relative content of the tetragonal phase is a little higher than the rhombohedral phases.Effect of La₂O₃ and CeO₂ addition on the structure and electrical properties of (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ (NBT-7BT) ceramic were investigated. The crystal structure of the specimens remains the coexistence of rhombohedral and tetragonal phases. Nevertheless, with the increasing amout of La₂O₃ and CeO₂, the relative content of tetragonal phases are gradually enhanced. Compared with NBT-7BT specimen, the specimen added with a small amount of La₂O₃ shows an increase of electromechanical coupling factor (k_p) and piezoelectric constant (d₃₃), while a considerable decrease of delectric loss (tgδ) accompaned by a enhanced mechanical quality factor (Q_m) were detected for the specimens added with CeO₂. However, further increasing the amount of La₂O₃ and CeO₂ lead to a rapid degradation of piezoelectric properties and adeformation of P-E hysteresis loops, which may results from the formation of antiferroelectric micro-region in the specimens at room temperature.The structure and electrical properties of(Nao.5Bio.5)o.93Bao 07TiO3+0.2wt%Ln2O3 (Ln=La^ P^ Nd, Sitk Eu^ Gd) ceramics were examined. It was ascertained the piezoelectric properties of the specimens rely on the deformation mode and degree of the crystal structure. A degradation of the piezoelectric properties was found for the specimens with smaller lanthanide size.