Research On Modified Lead Metaniobate Piezoelectric Ceramic With High Curie Temperature

In this dissertation, lead metaniobate (PbNb₂O₆ (PN)) based piezoelectric ceramic with high Curie temperature were synthesized by conventional ceramics preparation technique. The relations among preparation method, crystal structure and the piezoelectric properties were investigated, and the relations among the composition, the crystal structure and the piezoelectric properties were also studied. The effect of ferroelectric feature on the piezoelectric properties has been established in terms of experimental results.The dependence of crystal structure and piezoelectric properties on synthesized temperature, sintering temperature and cooling method of PN-based ceramics was studied. The results show appropriate synthesized temperature is in the range of 850 900℃for 2 h and sintering temperature for ceramic is in the range of 1245～1255℃for 2 h. The orthorhombic symmetry tungsten bronze structure with ferroelectric characteristic of the PN-based ceramic is obtained at furnace-cooling condition. The piezoelectric properties of the PN-based ceramics highly depend on poling field and temperature, while no remarkable effect of poling time on the piezoelectric properties. Appropriate poling field is 4.5 kV/mm, poling temperature is 160～170℃and poling time is 15 min.The structure, piezoelectric and dielectric properties of 0.3wt%MnO₂-(Pb_1-xBa_x)Nb₂O₆ (PBMN) ceramics were investigated. XRD results reveal that the crystal structure of ceramics transformed from rhombohedral non-ferroelectric to orthorhombic ferroelectric by sintering. The result of dielectric constant vs temperature shows that all the compositions have a high Curie temperature in the range of 490～550℃. The piezoelectric properties of PBMN ceramics have been enhanced with the increasing of dopant Ba²⁺ content. When x=0.05, the piezoelectric constant d₃₃ attains 70 pC/N which is the maximum of all the compositions, the Curie temperature T_c is 510℃, the dielectric constantε₃₃^T/ε₀ is 326 and dielectric loss tang is 1%.The crystal structure, piezoelectric, dielectric and ferroelectric properties of (1-2y)PbNb₂O₆-ySrTiO₃-yTiO₂ (PST) ceramics were also studied. The dependence of dielectric constant and temperature at 1,10,100 kHz frequency was analysized, respectively. It is found that this system ceramics are relaxational ferroelectric materials and they have high Curie temperature about 500～560℃. It is showed that it has the relatively higher remanent polarization P_r and relatively lower coercive field E_c from P-E hysteresis loops results at y=0.02. This material has good piezoelectric and dielectric properties of which are piezoelectric constant d₃₃=83 pC/N, electromechanical coupling factor k_t=34.9%, mechanical quality factor Q_m=12, dielectric loss tanδ=1.5% and the Curie temperature T_c=550℃, respectively.