| In condensed matter physics,multiferroic materials have been a hot research topic due to their wide application.Among them,bismuth ferrite(BiFeO3)is attracting attention because of its excellent performance and abundant physical properties.It is a rare material that simultaneously possesses good ferroelectricity and magnetism at room temperature.However,the preparation of the high-quality ceramic samples of BiFeO3 has been a difficult subject that puzzles scientists.Due to the excellent ferroelectric properties and advantages in domain structure measurement,the thin film samples of BiFeO3 have been highly concerned in recent years.Conversely,the research of the ceramic samples has been greatly reduced,owing to the difficulty in obtaining the ceramic samples with good ferroelectric properties.However,the research of the piezoelectric property of BiFeO3 has to rely on the ceramic samples.So,the focus of this thesis is returned to the ceramic samples in order to obtain high-quality ceramic samples and effectively improve some performances of the BiFeO3 ceramics through series of test,such as the ferroelectric,piezoelectric and dielectric properties and so on.This thesis is organized as follows.In the first chapter,the introduction to multiferroic materials and perovskite structure is presented at the beginning.The following part is devoted to the background knowledge of BiFeO3,including its structural properties,its predecessor's research background,major application fields,common preparation methods and problems to be solved.In addition,the ferroelectric and piezoelectric properties of BiFeO3 and previous research results are also introduced.Finally,some applications of BiFeO3 are discussed.In the second chapter,the instruments used in the measurements and the methods of preparing the samples are mainly introduced.The rapid hot-press sintering method is used to prepare BiFeO3 ceramics,while the method of polymer assisted deposition(PAD)is used to prepare the thin-film samples.A number of measuring systems,such as X-ray diffraction(XRD),scanning electron microscopy(SEM),atomic force microscopy(AFM),piezoresponse force microscopy(PFM),and physical property measurement system(PPMS)and so on,are applied to investigate the ferroelectric,piezoelectric and dielectric properties of BiFeO3.In the third chapter,we systematically discuss the sample test.By SEM and density comparison,a highly dense sample is successfully prepared.It is revealed from the ferroelectric,dielectric,and piezoelectric measurements that the sample exhibits many good electrical properties,such as high ferroelectric coefficient(P-50?C/cm2),good piezoelectric coefficient(d33?55pm/V)and good dielectric properties and so on.Besides,a rich domain structure is observed in the sample through the PFM measurement.The reason for the excellent performance of the sample is likely to lie in a certain orientation the sample possesses and the consequent lack of internal disorder during the sintering process in which the hot pressing and direct current are applied.In the fourth chapter,the polymer assisted deposition method used to grow the BiFeO3 thin film samples is introduced firstly.The BiFe03 epitaxial thin films,which are shown to have good surface flatness,are also prepared using the polymer assisted deposition method.The domain properties of the sample are also discussed.We can write a domain structure by applying a voltage,although it is hard to obtain the spontaneous domain.The fifth chapter is devoted to the summary and perspectives.First,it is revealed from our research on BiFeO3 ceramics and films that the ceramic samples of BiFeO3 can have good,comparable electrical properties to single crystal samples.Second,the preliminary preparation of the thin film samples provides a new approach for the future research of thin film samples.Besides,these two preparation methods:hot-pressing and polymer-assisted deposition can also be helpful to solve other problems in condensed matter physics. |
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