~Lead zirconate titanate (PbZrxTi1-xO3, PZT) material has a broad application prospect in the fields lor='red'>of dynamic memory, thermal sensor, tunable microwave, and radar phase shifter due to its excellent ferroelectric, dielectric, pyroelectric, and piezoelectric properties. With the rapid d eVelopment lor='red'>of co mmunication systems and microelectronics technology, PZT can no longer meet the design requirements lor='red'>of high-performance microwave tuning devices, and controlling modification is an important means to improve its performance. In this paper, the electronic structure, dielectric properties, optical properties and ferroelectric properties lor='red'>of Sr and Ce co-doped PZT ceramic materials were studied by the first-principles calculation and experimental preparation. In this paper, the ratio lor='red'>of Sr single doping was 5%, 10%, and 20%. The single doping lor='red'>of Ce was 5%, 10%, 20%; The Sr-Ce co-doping ratio was 10%Sr-5%Ce, 10%Sr-10%Ce, 10%Sr-20%Ce.
In terms lor='red'>of theory, the Sr-Ce co-doped PZT system was studied by the first-principles method based on density functional theory. The theoretical model lor='red'>of PZT with different Sr-Ce doping ratios was established by the supercell method, and the electronic structure, dielectric, optical and ferroelectric properties lor='red'>of the doped system were calculated and analyzed. The main research conclusions summarized as follows:
(1) The band gap value lor='red'>of the Sr-doped PZT increases with the increase lor='red'>of Sr ratio, and there is a strong ionic bond between O atom and A-site atom in PZT system. The static dielectric constant decreases from 6.197 to 5.981; in the near-ultraviolet light region, the refractive index, extinction rate, and reflectivity lor='red'>of PZT system decrease, the transmittance is improved; the ferroelectric properties lor='red'>of PZT system can be effectively improved by increasing the ferroelectric spontaneous polarization value from 28.6 μC/cm2 to 66.2 μC/cm2.
(2) With the increase lor='red'>of Ce ratio, the forbidden band breadth lor='red'>of Ce doped PZT system increases. The energy bands near Fermi level are mainly contributed by O-2p, Ti-3d, Zr-4d orbital electrons, and Ce d orbital electrons; When Ce ratio is 5 %, the charge transfer between B-site atom and O atom is strong, and the covalent bond interaction is enhanced. The static dielectric constant decreases from 7.1 to 6.3; in the near-ultraviolet region, the refractive index, extinction ratio, and reflectivity lor='red'>of the system decrease. When the Ce doping content increases to 20%, the ferroelectric spontaneously polarized to 51 μC/cm2, which is obviously higher than that lor='red'>of undoped PZT system.
(3) When the ratio lor='red'>of Sr and Ce co-doped PZT system is 10%Sr-10%Ce, the band gap value decreases from 1.466 eV to 1.26 eV, and the band gap width becomes narrower. There is a strong resonance peak between O atom and B-site atom with strong localization. The charge transfer around B atom and O atom can effectively change the bonding polarization direction lor='red'>of the charge when the ratio is 10%Sr-20%Ce.The static dielectric constant increased from 6.854 to 7.243; Meanwhile, its can improve the optical storage efficiency and optical transmittance lor='red'>of the system at 20 eV~30 eV; When the co-doping content is 10%Sr-20%Ce, the ferroelectric spontaneous polarization increases from 28.6 μC/cm2 to 64.5 μC/cm2, which can effectively improve the ferroelectric properties lor='red'>of the materials.
In the experiment, solid-phase sintering was adopted to prepare the PZT and Sr, Ce co-doping PZT ceramic. The effects lor='red'>of PZT and Sr, Ce co-doping on the electrical properties lor='red'>of PZT ceramics were explored by changing different high temperatures and doping ratios. The microstructure, crystal structure, dielectric properties, ferroelectric, positron annihilation lifetime spectrum and high pressure raman spectroscopy lor='red'>of the ceramics were tested and characterized. The main conclusions summarized as follows:
(1) The characterization and properties lor='red'>of PZT ceramics were studied. It was found that the crystal lattice lor='red'>of PZT ceramics grew well and the surface was compact when the sintering temperature was 1000 °C. The dielectric constant and loss lor='red'>of PZT ceramic materials are larger, which is more ideal for improving the ferroelectric properties lor='red'>of PZT ceramic materials; Positron annihilation show that there are defects in PZT ceramics, and the defects are mainly B-position defects; Raman spectrum analysis shows that the PZT underwent obvious structural phase transition at the pressures lor='red'>of 2.61 Gpa and 8.68 Gpa in the range lor='red'>of 0~30 Gpa.
(2) Through the characterization and properties lor='red'>of Sr-doped PZT ceramics, it was found that at 1100 °C, the surface lor='red'>of 20%Sr-doped PZT ceramics is the densest, the diffraction peak is sharp, and the perovskite structure is formed. The relative dielectric constant is the largest and the loss is small. The saturation polarization and residual polarization are the largest. The results lor='red'>of positron annihilation test showed that Sr doping made the B-site defects become larger, but the lifetime strength lor='red'>of the defects is basically unchanged; Raman spectrum shows that a new structural phase appears when the pressure is 2.13 Gpa, and the Raman peak lor='red'>of PSZT basically disappears when the pressure is 6.88 Gpa.
(3) The characterization and properties lor='red'>of Ce-doped PZT ceramics were studied. It can be found that when the sintering temperature is 1000 °C, the surface lor='red'>of 5%Ce-doped PZT ceramics is the densest. Besides, the diffraction peak is sharp, the grain grows well, and the perovskite structure is formed. Its dielectric properties and ferroelectric properties have been improved effectively; the results lor='red'>of positron annihilation showed that Ce doping made the defects lor='red'>of PZT samples grow larger and the defect concentration decreased; Raman spectrum showed that PCZT phase transition occurs at the pressure points lor='red'>of 2.42 Gpa, 5.54 Gpa and 9.91 Gpa, and raman peaks increase.
(4) By studying the characterization and properties lor='red'>of Sr and Ce co-doped PZT ceramics, it can be found that when the sintering temperature is 1100 °C, 10%Sr-5%Ce doped PZT ceramic has the densest surface. Its sharp diffraction peak and good growth show that the perovskite structure was formed. The dielectric constant is the highest and the loss is relatively small, which is more ideal for improving the dielectric performance lor='red'>of the system. It has higher residual polarization and a smaller coercive field, which can effectively enhance the ferroelectric properties lor='red'>of ceramic materials; the positron annihilation results show that the co-doped PZT defects grow larger and the concentration lor='red'>of the captured defects decreases; Raman spectrum shows that the phase transition lor='red'>of PSCZT ceramics occurs at the pressure points lor='red'>of 4.4 Gpa and 5.54 Gpa, which has a great effect on the material structure change.
Through the combination lor='red'>of theory and experiment, this paper analysis the Sr, Ce co-doping PZT materials doped modified microscopic mechanism, and the preparation lor='red'>of the PZT ceramics. Exploring the effects lor='red'>of different high temperatures and doping ratios on Sr and Ce co-doped PZT ceramics is lor='red'>of certain significance for the research and application lor='red'>of PZT-based ceramics with high adjustable performance, which is expected to promote the wide application lor='red'>of pyroelectric ceramics in the fields lor='red'>of MEMS devices and dynamic memory.
Key words: PZT; Doped; First-Principles; Solid-Phase Sintering; Positron Annihilation;
High pressure-Raman
Thesis: Fundamental Research
Foundation Project：
The National Natural Science Foundation lor='red'>of China (Grant No. 11974275, No. 61834005);
The Shaanxi Innovative Talents Promotion Plan-Science and Technology Innovation Team Project (Grant No. 2019TD-026);
The Shaanxi Provincial Innovation Project for Science and Technology Overall Planning (Grant No. 2012KTCL01-12);
谷歌
火狐
