Research On Hydrothermal Synthesis Of Barium Titanate And The Formation Mechanism Of Intermediate Nanowires

Piezoelectric materials were widely used in Civil Engineering: They can be sensors and power harvesters by positive piezoelectric effect,making the realization of wireless structure monitoring network possible.At the same time,by negative piezoelectric effect,we can change their shape to actively control the structures.For a long time,the application of lead-based piezoelectric ceramics in civil engineering caused lots of environmental pollutions,and they are going to be banned by EU countries.Barium titanate(BTO)with benefits of high piezoelectric coefficient,non-toxic and pollution-free,have attracted a number of attentions in the researches on piezoelectric materials.The method of hydrothermal synthesis of barium titanate has many advantages,but at present,there are many defects in barium titanate synthesized by hydrothermal method,including OH-and barium ion vacancy.Meanwhile,there are some different assumes on the mechanism of hydrothermal transformation,causing the lack of theoretical guide for the hydrothermal synthesis of high-performance barium titanate.Complex precursors can improve the morphology of barium titanate,but the price of those precursors are very high.So,we used cheap Ti O2 as precursor in this paper,by change hydrothermal conditions,to synthesized barium titanate with narrow size distribution,good dispersion and uniform morphology,with the help of a variety of characterization means.A new process of two-step transition which was induced by low concentration precursors was found.Graphene oxide also play an important role in this process.Finally,we suggest that nanowire single crystal have a new crystal structure.This paper mainly includes the following five aspects:(1)The study of hydrothermal conditions and their effects: By controlling the use of Ti O2,reaction time and alkali concentration,we can learn the influence of hydrothermal conditions on the morphology and size distribution of barium titanate.(2)The research on effect of surfactant: For the different solubility of surfactant such an oleic acid,tert-butylamine and hydrazine,their influences on the morphology of the products in this mixed phase reaction system were studied.(3)The exploration of the functions of graphene oxide: the feasibility of using graphene oxide as a new surfactant was systematically explored.Further,we studied the functions of graphene oxide and ethylene diamine(EDA)in this reaction(4)The optimization of the formation conditions of nanowires: By adjusting the reaction conditions such as alkali state,amount of precursor,reaction time and temperature,after a large number of experiments,we found the best condition of producing smooth,flexible and ultra-high aspect ratio nanowire single crystal.At the same time,Elements characterization and lattice parameter analysis of nanowires were taken out to study this new single crystal.The mechanism of the two-step transformation from Ti O2 particles to nanowires and then recrystallize to BTO particles was proposed.