Zr ^{4 +} , Al ^{3 +} Doped Na _0.5 Bi <0.5> TiO < Study On The Structure And Electrical Properties Of Lead - Free Piezoelectric Ceramics

Piezoelectric ceramics are very important among functional materials. Because PZT-based piezoelectric ceramics can cause environmental pollution, the study on lead-free piezoelectric ceramics becomes a key subject. Recently, Na0.5Bi0.5Tio3(BNT)-based lead-free piezoelectric ceramics have been studied widely. In this work, we prepared BNT-based ceramics via a conventional solid-state reaction method. Effects of composition and preparation parameters on microstructure, crystallite structure, dielectric, piezoelectric and ferroelectric properties were studied.(1)(0.92Nao.5Bio.5Tio3-0.06BaTio3-0.02Ko.5Nao.5Nbo3)-xwt%Zr02(BNBKT-xZr, x=0,0.01,0.02,0.04) were synthesized via a conventional solid state reaction method. The rhombohedral-tetragonal MPB exists in the BNBKT-xZr ceramics. The doping of Zr4+increases the percentage of the tetragonal phase. The doping of Zr4+does not affect grain size and grain shape obviously. Two dielectric anomalies are observed in the dielectric constant-temperature curves for the unpoled samples. The maximum values of dielectric constant and corresponding temperatures change with the variation of the Zr4+amount. The doping of Zr4+causes a decrease in the ferroelectric properties. The mechanism was also discussed.(2)(1-x)(0.93Na0.5Bi0.5Tio3-0.07BaTio3)-xBiA103(BN7BT-xBA, x=0,0.01,0.02,0.06) lead-free ceramics were synthesized via a conventional solid state reaction method. Effects of BiA103doping on crystallite structure, microstructure, dielectric and ferroelectric ceramics were studied. All ceramics exhibit typical diffraction peaks of ABO3perovskite structure. Grain size and grain shape change with the change in the BiAlO3amounts. Both Curie temperature and maximum dielectric constant vary with the change in the B1AlO3contents. Ferroelectric properties are improved by the doping of the appropriate BiAlO3amount. The mechanism was also discussed.(3)0.93Nao.5Bio.5Ti03-0.07BaTi03(BN7BT) ceramics were synthesized via a conventional solid state reaction method. Effects of sintering temperature and heating rate on structure and electrical properties of the samples were studied. In addition, effect of hot-pressing sintering parameters on microstructure of the ceramics was also explored. With increasing sintering temperature, density of the ceramics is increased. The optical sintering temperatures are between1170-1190℃. Effects of sintering rate (1℃/min,3℃/min,6℃/min) on microstructure of the ceramics were also explored. As sintering rate is low, grain size is small and uniform, but there exists some pores in the ceramics. As sintering rate is high, the ceramics become dense and show un-uniform grains. In case of hot-pressing sintering, the pollution of carbon on samples was prohibited by using BN coating. In the present study, we did not obtain good BN7BT ceramics with using the parameters of0.5t,1000℃for30min and60min. The further study about hot-pressing sintering should be carried in future.