Investigation On Preparation And Properties Of BiFeO₃-Based Thin Films On Al Foils

Ferroelectric materials have been one of the most popular research topics in condensed matter physics and solid-state electronics, the reason is that these materials have superior performance, such as, ferroelectric properties, piezoelectric properties, etc. Nowadays, lead-based materials have been put into application, however, the volatility of lead can not only causes lead vacancies but also bring environment contamination and harmful to human health.The high remnant polarization and piezoelectric response of BiFeO₃?BFO? materials have attracted widely attention of researchers. BFO materials are very promising in replace of lead-based materials. While the severe leakage problems of pure BFO thin films set back its future application. In order to get the good performance of BFO thin films as well as lead-based materials, researchers put their efforts into doping modification of thin films. However, the choice of technical conditions and substrates in preparation will directly influence the crystalline degree of thin films. Moreover, the thickness of thin films in application should be at least above 1 micron.In this paper, we studied the BFO-based thin films with lanthanum doping. The influences of hot plate temperature, annealing temperature, different substrates, solution concentration and acetic acid content were mainly studied. And then we explored how to prepare Bi_0.9La_0.1FeO₃ thick film in Sol-gel methods, find out the problems and figure out the possible solutions. In addition, we investigated the influence of annealing temperature on structure and electrical properties of BFO thin films fabricated on Al substrates. Main contents and conclusions are as follows:1. As the solution concentration increasing, the films' grain size will increase. The influence of solution concentration, acetic acid content, different substrates on structure of BFO thin film was studied. It can be found that with the increasing of solution concentration, the BFO films' grain size increased. The content of acetic acid has a great effect on structure of films. The increased content of acetic acid contributes to the grain growth of BFO film on ITO/glass substrate. When the content of acetic acid is 60%,?100?-oriented BFO film can be found in BFO film on Al substrate. While further increasing the content of acetic acid, it is bad for grain growth of BFO film on Al substrate.2. On ITO/glass substrates, we prepared BLFO thin films with a series of hot plate temperature, as 175?, 200?, 225?, 250?, 275? and studied the effects of different hot plate temperature on the properties of BLFO thin films. As a result, the lower temperature of hot plate will make the lower crystallization of thin films and it will bring more air holes?such as 175??, on the other hand, the higher hot plate temperature will increase surface roughness and it will appear carbonation phenomenon?such as 250 ? and 275 ??. As a consequence, the crystallization properties is better between the hot plate temperature 200?²25?.3. On ITO/glass substrates, we prepared BLFO thick films with 1.5mol/L precursor solution concentration. The in-plane lattice size of great crystallization is about 400 nm. However, it leads to a short storage time of precursor solution and it will precipitate after 10 days. In order to figure out the sediment reasons, we did a contrast experiment, which turned out that the environment temperature in the preparation and storage process has an influence on storing time of precursor solution.These results show that low temperature is an important way to improve the stability of high concentration precursor solution in sol-gel method.Finally, apreferred?110?-orientation BLFO film can be obtained with a comparatively high remanent polarization?Pr? of 42.85?C/cm2.4. On Aluminum substrates, we prepared BLFO thin films with a series of annealing temperature, as 475?, 500?, 525?, 550?, and we studied the effects of different annealing temperature on structure and electrical properties of BLFO thin films. It is demonstrated that comparing with BFO-based thin films in other substrates, the BLFO thin films in Aluminum substrates have bigger coercive filed and strong fight against wear ability, and its leakage current density lower 1² orders of magnitude. We tested the hysteresis loop of BLFO thin films prepared on Aluminum substrates in different signal frequency, and analysis the relationship between signal frequency and hysteresis loops. Generally speaking, the hysteresis loops of thin films show the tendency of shrinkage under high frequency, and the increase frequency will decrease the value of remnant polarization.