Microstructure and electrical properties of Ta-doped Na0.5Bi4.5Ti4O15 ceramics

Bismuth layer structured piezoelectric ceramics, Na0.5Bi4.5TaxTi4-xO15+0.5x (NBT-Ta-x)(x=0-0.20), were fabricated via a solid state sintering process. The effect of Ta5+ doping for B site on the microstructure, electrical conductivity,dielectric and piezoelectric properties of NBT-Ta-x ceramics was investigated by means of XRD, SEM and an automatic temperature control testing system. The results show that Ta doping brings about the decrease in grain size and aspect ratio of grain with a preferable orientation growth along c-axis. Meanwhile, both theoretical density and measured density of the ceramics is increased with increasing tantalum doping content, with the highest relative density of 96.1% at x=0.05, showing that the solid solution limit of tantalum in NBT lattice is in the proximity of x=0.10. The Curie temperature is decreased slightly from 680℃ to 658℃ with the increase of Ta5+ doping content x to 0.20. The electrical resistivity of NBT-Ta-x ceramics is increased as much as about two orders of magnitude by Ta5+ modification and the piezoelectric constant d33 values is increased significantly from 13.8 pC/N to 23 pC/N. The x=0.04-0.05 samples exhibit the optimal electrical performance:Tc=670-672℃,d33=21.8-23 pC/N, kp=7.9%-8.3%.