The Observation Of Domain Switchings Within BaTiO₃ Nanofibers Under Different Electric,Force And Thermal Fields

Ferroelectric materials have attracted a great deal of attention due to their excellent ferroelectric,piezoelectric,dielectric and pyroelectric properties.With the rapid development of the fabrication technology of ferroelectric materials,one-dimensional ferroelectric materials with lower dimension and smaller size than thin films have become a new research hotspot.As one of the typical one-dimensional ferroelectric materials,ferroelectric nanofibers have been widely concerned.The main work presented in this thesis is focused on the synthesis and characterization of the barium titanate?BaTiO₃?nanofibers with typical perovskite structure.BaTiO₃ nanofibers are prepared by electrospinning.Piezoresponse force microscopy?PFM?has been employed to study the piezoelectric and ferroelectric properties and observe the domain switchings within the BaTiO₃ nanofibers under different external fields.As the electric field is one of the most common external fields,it is necessary to study the influence of the electric field on the domain within the BaTiO₃ nanofibers.The functional devices based on ferroelectric nanofibers can be affected by external force and temperature fields,so we also study the domain evolution process within the BaTiO₃ nanofibers under these external fields.The main research works are as follows.1.Firstly,we investigate the effects of different electrospinning parameters on BaTiO₃ nanofibers in the horizontal electrospinning.Then electrospinning is carried out under the best parameters.BaTiO₃ nanofibers are prepared by annealing at 600??650??700? and 750?.Secondly,we investigate the basic physical properties and ferroelectric and piezoelectric properties of the samples at four different annealing temperatures.The results show that the nanofibers annealed at 700? are well crystallized and with good morphology.The amplitude–voltage butterfly loop is pretty symmetrical.Therefore,they are suitable for the observation of domain switchings under different external fields.2.In order to investigate the domain switchings within BaTiO₃ nanofibers under different electric fields as well as the effect of size on properties of nanofibers,the large-scale BaTiO₃ nanofibers and the small size BaTiO₃ nanofibers are selected to observe the domain switchings under different electric fields.The phase-voltages of them are also obtained.The results show that the voltage required to accomplish the180° domain switching within the small size BaTiO₃ nanofibers is much lower than that of the large-scale BaTiO₃ nanofibers.And the domain state is easier to maintain after the removal of the electric field.Therefore,the preparation of functional devices based on small size BaTiO₃ nanofibers can reduce the power consumption.3.The external force fields and temperature fields are applied respectively by PFM.Under the force field,the polarization vectors have the trend of reversing to the horizontal direction,which is proportional to the magnitude of the force field.Under the temperature field,the increase of the temperature leads to the change from a-domain to c--domain within the BaTiO₃ nanofibers below the Curie temperature.After exceeding the Curie temperature,nanofibers transform to the paraelectric phase and the ferroelectricity disappears.During the cooling process,BaTiO₃ nanofibers have the tendency to transform from cubic phase to tetragonal phase.But the transformation is with a slow rate and has not yet been completed until the room temperature.