Synthesis Of Water-based Lead-free Piezoelectric Ceramics Thin Films Via Sol-gel Method And Its Properties

This dissertation focused on study of the microstructure and properties of large piezoresponse sodium bismuth titanate(Na_0.5Bi_0.5TiO₃,NBT)lead-free piezoelectric thin films obtained by the economical and environment-friendly water-based sol-gel method.Firstly,we introduced the water-based sol-gel method for preparing of polycrystalline NBT thin films onto the Pt（111）/Ti/SiO2/Si substrates and methods of characterization for thin film structure and properties.A new annealing process called stepwise crystallization was designed to depositlarge thickness and high quality thin films.The effect of thickness on dielectric,ferroelectric and piezoelectric properties was investigated and relative mechanism was discussed in detail.Passive interfacial layer model and charge injection model were found playing key roles inthe relationship between film thickness and enhanced electrical properties of NBT thin films.The dielectric property and piezoelectric property were improved by increasing thickness of thin films.Secondly,highly（100）preferred orientation of(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ thin films were prepared by introducing Pb_0.8La_0.1Ca_0.1Ti_0.975O₃（PLCT）seed layer.The samples prepared by introducing PLCT seed layer and different annealing methods were characterized,and found thatthe intrinsic contributionsto enhance the performance of piezoelectric is much more than the extrinsic contributions,but conversely for dielectric properties.The NKBT thin films prepared by multiple crystallization with PLCT seed layer showed the best electric property with εr of 598,tanδ of 0.08,and 33 d of 136 pm/V.（1-x）Na_0.5Bi_0.5TiO_3–xK_0.5Bi_0.5TiO₃（NBT-xKBT）and（1-x）Na_0.5Bi_0.5TiO_3–xBaTiO₃（NBT-xBT）are A-site doped perovskite systems.Experimental results showed that 0.85NBT-0.15 KBT and 0.94NBT-0.06 BT components exhibited optimum dielectric and piezoelectric properties.Meanwhile,the study of the influence of excess Na/K on the structure and properties of thin films was carried.In addition,the maximum strain is found 1.4%-1.8% in 0.94NBT-0.06 BT thin films much higher than that of the bulk ceramics.The influence of Mn and Mg doping through the B-site substitutionon the microstructures and properties of NBT thin films was investigated.From the experimental results,we can conclude that the doping of Mn can effectively reduce the leakage current density of NKBT thin films and Mg doping can improve the piezoelectric properties of NBT thin films.And through Mn,Mg co-doping,NBT films can have better comprehensive performance.