Preparation And Properties Of BNT Based Lead - Free Piezoelectric Ceramics

Bismuth sodium titanate Bi0.5Na0.5TiO3(BNT)-based lead-free piezoelectric ceramicshave received much attention due to their strong ferroelectricity and high Curietemperature. In this paper, ion substitution、multiple component and sintering aidsmodification were studied to improve the electrical properties and sintering process ofBNT-based piezoelectric ceramics. All ceramics in this paper were prepared by theconventional ceramics fabrication method. Main results are listed below:1. The effects of (Sm3+、Co3+) and (Bi3+、Cr3+) co-doping and Al3+doping onmicrostructure and electrical properties of BNT-based ceramics were systematicallyinvestigated. The results showed that all the samples possessed pure perovskite phasestructure. The co-doping of Sm3+、Co3+to0.94Bi0.5Na0.5TiO3-0.06BaTiO3（BNBT6）ceramics caused a remarkably promoted grain growth. In addition, the piezoelectricconstant d33, planar electromechanical coefficient kpand mechanical quality factor Qmcould be improved at the same time. In Sm3+、Co3+co-doped BNT system, the ceramicswith x=0.4%exhibited optimum properties d33=144pC/N, kp=29.1%, and Qm=219. Theco-doping of Bi3+、Cr3+to0.93Bi0.5Na0.5TiO3-0.07BaTiO3（BNBT7）ceramics caused theobvious lattice distortion. c/a of crystal lattices have increasing trend with the addition ofBi3+、Cr3+. The electrical properties of BNBT7ceramics have been greatly improved bycertain amount of Bi3+、Cr3+co-doping. The ceramics with x=0.6%exhibited optimumproperties the remanent polarization Pr=41.7μC/cm2， the coercive field Ec=17.6kV/cm,d33=205pC/N, kp=19.3%. With the addition of Al3+, the piezoelectric constant d33, planarelectromechanical coefficient kpof Bi0.5Na0.36K0.09Li0.05TiO3（BNKLT）ceramics decreasedslightly. Certain amount of Al3+doping could improve the mechanical quality factor Qm.2.(Ba0.90Ca0.10)(Ti0.92Sn0.08)O3and LiSbO3were introduced in BNT system.(1-x)Bi0.5Na0.5TiO3-x(Ba0.90Ca0.10)(Ti0.92Sn0.08)O3[(1-x)BNT-xBCST] and (0.94-x)Bi0.5Na0.5TiO3-0.06BaTiO3-xLiSbO3[(0.94-x)BNT-0.06BT-xLS] ceramics were fabricatedand investigated. The results showed that (1-x)BNT-xBCST ceramics possessed pure perovskite phase structure when0.00≤x≤0.14. What’s more, the rhombohedral-tetragonalmorphotropic phase boundary (MPB) existed in the ceramics when0.07≤x≤0.14. Thepiezoelectric and ferroelectric properties of BNT ceramics have been greatly improvedwith the addion of BCST. At x=0.08, enhanced piezoelectric properties were obtained inthe system with a large piezoelectric coefficient d33of219pC/N and a planarelectromechanical coupling factor kpof20%, a coercive field Ec=21.3kV/cm.The addionof LiSbO3to BNBT6ceramics caused a remarkably promoted grain growth. Thepiezoelectric properties of BNBT6could be improved by certain amount of LiSbO3. Whenx=0.015, the ceramics showed the optimum properties, d33=149pC/N, kp=23%, and Qm=143.3.（1-x）BNT-xSrFeCo0.5Oypiezoelectric ceramics were fabricated and investigated.The results showed that all the ceramic samples possessed perovskite phase structure andno secondary impurity was observed. SrFeCo0.5Oyas sintering aids promoted grain growthand decreased sintering temperature remarkably. The sintering temperature of BNT couldbe decreased to1050oC by SrFeCo0.5Oyaddition. In addition, SrFeCo0.5Oyhad theco-doping effect on the electrical properties of BNT ceramics, the ceramics exhibitedoptimum properties at x=0.06, d33=92pC/N, kp=0.15, Qm=383.