The First-principles Calculation And Nanotubes Preparation Of PZT

Lead zirconium titanate(PZT) ferroelectric materials is mainly used in ferroelectric memory and pressure sensors because of its high Curie temperature, good ferroelectric and piezoelectric properties. At present, one-dimensional nanoscale ferroelectric materials have become one of the hot spots in the field of ferroelectric research due to the large potential in the fabrication of nano-generator and ferroelectric memory of high storage density. In this paper, the first-principles method was used to calculate the microscopic properties of PZT. And the preparation of PZT nanotubes were studied and discussed by the AAO template method combined with the sol-gel spin coating process.The relationship between the ferroelectric properties and the microscopic properties of PZT was studied. PZT is a solid solution of PbTiO3(PTO) and PbZrO3(PZO), in which PTO has a major influence on the ferroelectric properties of PZT. In this paper, total energy and electronic structure of PTO with paraelectric and ferroelectric phase were calculated using first-principles method, the result showed that the total energy of the PTO with ferroelectric phase is less than that of PTO with paraelectric phase, which indicated that the structure of PTO with ferroelectric phase is more stable. And the paraelectric PTO has a direct band gap structure, the band gap is 1.696 eV. The PTO with ferroelectric phase has an indirect band gap structure, the band gap is 1.790 eV. The analysis of density of states showed that the hybridization of Ti3 d and O2 p electron orbit in PTO with ferroelectric phase is enhanced which maintains the ferroelectric properties of PTO. The study of optical properties showed that the maximum peak of the imaginary part of dielectric function in two structures correspond to the electronic transitions from O2 p orbitals to Ti3 d orbitals and the dielectric peak of PTO with ferroelectric phase is decreased, which is possiblely due to the indirect band gap structure. The maximum peak of the real part of dielectric function in ferroelectric PTO is located at 3.26 eV, which is in agreement with the experimental data. The absorption peak of the PTO with ferroelectric phase has the blue shift.The relationship between the microscopic properties and the composition of PZT of cubic phase was studied. PbZrxTi1-xO3(x = 0, 0.25, 0.5, 0.75, 1) with cubic phase were build with supercell method, then the supercell configuration of lowest energy at each proportion were determined. The properties of different proportions were calculated with the configuration of lowest energy. The changes in different proportions were analyzed. The results showed that the total energy of the system increased with the increase of Zr content. PZT lattice constant also increased, and obeyed the Vegard's law. The analysis of density of states showed that Zr4 d and Ti3 d have hybridization with O2 p respectively, resulting in a similar hybrid effect. The properties of PZT with different proportions were calculated using the virtual crystal approximation method. It was found that the lattice constant increased linearly with the increase of x, and the linearity was better. The change of band gap was similar to the result using the super cell method.Preparation of PZT nanotubes by template method was studied, and a highly ordered AAO template was prepared by the two step anodic oxidation method. Scanning electron microscope(SEM) chart showed that the cycle of AAO template is around 90 nm, the template aperture is around 80 nm, and the channels of the template are straight and parallel. The PZT/AAO composite structure was successfully prepared by the template method combined with the sol-gel spin coating process. The PZT nanostructures were obtained after the AAO template removed by NaOH solution. The morphology of PZT nanostructures was characterized by SEM, and the PZT nanotubes were found to have the same external diameter as the AAO template's, which was about 80 nm. The composition of the sample was analyzed by EDS which proved that sample is composed of AAO and PZT.