Impact Studies Of The Original Powder Morphology On The Microstructure And Piezoelectric Properties Of NBT Ceramics

The research and application of Bismuth Sodium Titanate Na_0.5Bi_0.5TiO₃（i.e.NBT） ceramics, one kind of lead-free piezoelectric ceramics systems, is takenseriously by more and more people. As a kind of A-site ions substitution replacedperovskite-type ferroelectrics, the NBT base ceramics, which have such goodproperties as the good temperature stability, the outstanding piezoelectricity andferroelectricity, the high frequency constant, the small dielectric coefficient and so on,are considered to be green ceramic materials of most hopeful substitution oftraditional lead-base piezoelectric ceramics. However, it’s also well known that NBTceramics’ high coercive field makes the material difficult to be polarized. Expertsand scholars at home and abroad, mainly improve the performance of NBT ceramicsin tow ways, A、B co-substitution modification the improvement of the preparationprocess. Hydrothermal synthesis method is widely used in the preparation of powdersbecause of its mild required conditions, neat and easily controlled morphology of theproduct, high purity of the product and so on.In this paper, Na_0.5Bi_0.5TiO₃powder with different micro-morphologies wasprocessed successfully right via the hydrothermal synthesis method, using titaniumtetrachloride（TiCl4）, five water bismuth nitrate （Bi（NO₃）₃5H₂O） as source oftitanium ion source and bismuth ion source respectively, sodium hydroxide （NaOH）as the sodium ion source and mineralizing agent. And it was researched the affectionof the concentration of NaOH （2M¹8M）, hydrothermal temperature （160℃²00℃）and hydrothermal time （0.5h⁷2h） on the morphology of NBT powder. On the basisof NBT powders with different morphologies prepared successfully via hydrothermalmethod, the influence of powder morphology on the microstructure and piezoelectricproperties of NBT ceramics were researched. The findings on the preparation of Na_0.5Bi_0.5TiO₃powders with differentmorphologies show that: the concentration of NaOH was the main factor whichaffected the micro-morphology of NBT powder, and when the concentration of NaOHwas lower than8M, the degree crystallinity of the product was very low and themicro-morphology of NBT powders is micro-spherical; when the concentration ofNaOH was12M and14M, the micro-morphology of NBT powders is the mixture ofmicro-cubic and nano-wire; and when the concentration of NaOH was18M, the mainmicro-morphology of NBT powder was micro-cubic aggregated by nano-cubic. Whenthe concentration of NaOH was14M, hydrothermal temperature and hydrothermaltime primarily affect the degree of crystallinity of the powder particle, the impact onthe morphology of the powders are not particularly evident. The analysis results of theNBT ceramics prepared by original powders with different morphologies indicate that:the micro-morphologies of original powder have significant effects on themicrostructure and piezoelectric properties of NBT ceramics, the NBT powderswhose micro-morphology is micro-spherical showed relatively good sinteringproperties, and it is good for preparing the NBT ceramics which have fine gains andgood relative density; because of the induction of liner grains in the hybridmicro-sphere line NBT powders, NBT ceramics prepared from this kind of powderswill form large grain polycrystalline structures, and these large grain structures makeits piezoelectric properties significantly higher than the fine grain NBT ceramicsprepared from micro-spherical powders.