Preparation And Properties Of (1-x)(K 0.5 Na 0.5 )NbO 3 -xLa(Al,Bi)O 3 Transparent Ferroelectric Ceramics

Transparent ferroelectric ceramics is a kind of transparent ceramics with electro-optic effect, excellent ferroelectric andmechanical properties, resistance of high temperature, resistance of corrosion and high hardness. These properties make the transparent ferroelectric ceramics a key material in the modern optics devices, the future optical computers, electronic information technology and the national military defense applications. Most of the current transparent ferroelectrics is the lead-based materials,such as Pb_1-xLa_x?Zr_yTi_z?O₃?PLZT?, ?1-x?Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ ?PMN-PT?, Pb?Zr,Ti?O₃-Pb(Zn_1/3Nb_2/3)O₃?PZT-PZN? Pb?Zr,Ti?O₃-Pb(Ni_1/3Nb_2/3)O₃ ?PZT-PNN?, etc. But many countries in the world legislated banning harmful materials used in the electronic devices, especially the lead-based materials. On the other hand, the research about lead-free transparent ferroelectric ceramics increased gradually. More recently, the KNN-based lead-free transparent ferroelectric ceramics have attracted significant attention. The main problem is the low liner transmittance of the KNN-based ceramics. In addition, the correlation between the structure and the electro-optic properties has not been studied in-depth, so as the mechanism of transmittance. So the research on excellent performance of ferroelectric ceramics with high transmittance is a demanding topic.In this work, potassium sodium niobate lead-free transparent ferroelectric ceramics were prepared by traditional solid method sintering in the air with atmospheric pressure. The subjects include:1) study the relation between preparation process of transparent ferroelectric ceramics and its transmittance and ferroelectric effects; 2) discus the relation among the different doping, the crystal structure and density linear transmittance of the ceramics; 3) Explain the rules effect on the dielectric and ferroelectric properties; 4) clarify the basic principles of improvement on linear transmittance of the lead-free KNN-based transparent ferroelectric ceramics. The results are as following:1. Traditional solid method was used for preparation of ?1-x?(K_0.5Na_0.5)NbO₃-xLa₂O₃ ?x = 0.005,0.010,0.015,0.020, KNN-L? ceramics sintering in air and normal pressures. Preliminary results showed that transparent KNN-L ceramics can be obtained at certain conditions including pre-sintering temperature and times, sintering temperature and times and running technology.An the KNN-L ceramics showde pure perovskite structure and characteristic pseudo cubic phase at room temperature. The KNN-L-0.015 ceramics showed the most uniform grain size distribution, clear boundary, and the highest relative density 98.5%. The linear transmittance of KNN-L-0.015 reached the great value,59.7%?780nm? in the visible region. As doping level ?x? increased to 0.020, the dielectric constant ??m? of KNN-L ceramics at room temperature reached maximum ?m = 1974, and it's T_c = 195 ?.2. ?1-x?(K_0.5Na_0.5)NbO₃-xtLaAlO₃ ?x = 0.025,0.050,0.075,0.100, KNN-LA? ceramics were successfully designed and prepared. Introduction of La ions and Al ions led to the orthorhombic phase of KNN-LA ceramics. The SEM images of all the KNN-LA ceramics showed inhomogeneity grain size and fuzzy grain boundary. The relative density reaches the maximum 97% of KNN-LA-0.05 ceramics while relative densities of other ceramics are below 96%. The maximum liner transmittance reaches 38.9% ?780nm? as x = 0.050. The electric hysteresis of KNN-LA ceramics was not the typical electric hysteresis loop, which showed the poor ferroelectric properties of KNN-LA ceramics. Above analysis shows that addition of LaAlO₃ weakened the linear transmittance and electric properties of KNN-LA ceramics.3.?1-x?(K_0.5Na_0.5)NbO₃-xLaBiO₃ ?x =0.000,0.005,0.010,0.015,0.020,0.025, 0.040,0.060, KNN-LB? ceramics were designed and prepared. In addition, the relation between microstructure, phase transformation, linear transmittance and the electric properties were studied. All KNN-LB ceramics showed pure perovskite structure when x ? 0.040. second phase diffraction peaks of impurity appeared at x = 0.060. With increase of LB, the typical orthorhombic phase transformed to pseudo cubic phase. As x increase to 0.025, the SEM images of KNN-LB-0.025 ceramics showed uniform grain size distribution and clear boundary. The fracture of KNN-LB-0.025 showed the lowest porosity, highest density and maximum relative density ?98.8%?. Optical picture and transmittance analysis indicated that KNN-LB-0.025 had the highest transmittance of 74.6% ?780nm? in visible region and 80%?1272nm? in the near infrared region and showed transparent outlook. When x = 0.005, the dielectric constant of KNN-L ceramics at room temperature reaches maximum 860, and it's T_c = 200 ?. The P-E hysteresis loop shape becomes more and more thin with x increase.