Research On Preparation And Properties Of BaTiO₃/PVDF Dielectric Composites

This paper intends to prepare a kind of energy storage dielectric material which has such properties: high dielectric constants as ferroelectric ceramics and good processing ability of Polymer. In order to get the composite dielectric material Ba Ti O3/PVDF and study its property, we use Ba Ti O3 powder as function phase, the rmoplastic polymers PVDF as matrix phase.We adopt some methods like TG, temperature rheometer to study the mixing procedure and hot pressing process of Ba Ti O3/PVDF, the results show that: Pre-shearing process can decrease the high temperature viscosity of PVDF polymer matrix which is good for composite molding. The molding temperature interval of Ba Ti O3/PVDF ranges from 160℃ to 300℃, and in this interval, collective viscosity is larger than 100Pa·s. If preparing Ba Ti O3/PVDF using hot pressing process under the condition of 250℃ with 100 MPa, density of samples will be greater than 95%.Besides, we also use XRD, SEM and impedance analyzer to study how diameter of Ba Ti O3 particle and its volume fraction affect dielectrical and mechanical properties of composite materials. Based on our research, we find: Ba Ti O3 powder has ?size effect? which means it can transform from ferroelectric phase to paraelectric phase driven by dimension. Its limiting size is approximately 100 nm. Dielectric constant and dielectric loss of composite material are influenced by powder?s diameter, volume fraction and internal interface of material. The influences of volume fraction of Ba Ti O3 on dielectric constant of composite materials accord with the modified Lichtnecker equation. While when Ba Ti O3?s diameter decreases and its volume fraction increases, breakdown strength of composite materials will decrease due to the existence of some tiny defects like unevenly distributed surface or pores.When using liquid precipitation method to modify nanometer Ba Ti O3 powder coating with Al2O3, we make a research on how parameters of coating craft affect the coating effect by applying TEM, XPS, XRD, etc. We find that concentration of Al3+ and PH have great effect on its coating result. When the concentration of Al3+ is 1mol/L, PH is 8 and sintering temperature reaches 500℃, we can get uniform and complete Al2O3-Ba Ti O3 powder. Al2O3 after sintering sticks to nuclear-shell structure powder of Ba Ti O3 in amorphous state.In this paper, we investigate the influences Al2O3 coating craft have on Ba Ti O3/PVDF composite materials? dielectric constant, dielectric loss and breakdown strength. The results show that: coating Ba TiO3 with Al2O3 can decrease dielectric constant of Ba Ti O3/PVDF, to some extent; it has little effect on dielectric loss of composite materials but can improve its breakdown strength evidently.