| Quantum functional materials possessing "composite" characteristics, having its own multiple parameters (including the charge, orbital and spin degrees of freedom) and speical field effect (including optical, electrical, magnetic, acoustic and thermal field), can be achieved diversified processing, and thus be widely using in the information domain, such as transmission, transformation, storage, control and so on. Studying on the multi-parameter quantum functional materials is of great significance to the development of quantum information technology. Unfortunately, up to now, the systematic study of the material system of composite quantum function has been insufficient and there is even many blank in some fields. Therefore, investigations on new’composite’quantum function oxide material systems are great important and helpful to explore new principles and fantastic physical effect and to develop new functional materials and fresh physical method.As potential candidates for quantum functional oxide materials, layered oxides have been drawn much attention recently, driven by its special layered structure which can realize at least two parameter-couplings on one crystallographic axis. Before 2009, layered oxides mostly focus on ferroelectric and dielectric material systems, however, such oxides with magnetoelectric coupling has been rarely reported. In 2009, using the co-doping technique, a new four-layer Aurivillius-phase Bi5Fe0.5Co0.5Ti3O1.5 which presents room-temperature ferroelectric and ferromagnetic responses, was synthesized by Mao et al. [Appl.Phys.Lett.95,082901(2009); Patent Number:CN101607818B]. Later, a new single-phase multiferroic ceramic, SrBi5Fe0.5Co0.5Ti4O18, was then synthesized by Lu et al. [Materials Horizons,2,232-236 (2015); Patent Number: CN102875145B], of which the multiferroic properties at or above room temperature and a large magnetoelectric coupling effect (～370 K, α～350μV cm-1 Oe-1) were observed. The studies not only make a breakthrough in the development of exploring the layered quantum functional oxide materials, but show a good idea that it is feasible to obtain materials with magneto-electric coupling effect through artificial design. In 2012, Yalin Lu from USTC brought forward the "multi-parameter quantum functional oxide materials" concept in the National Basic Research Program of China (2012CB922000), which was defined as that the new quantum functional oxide materials with the order’composite’structure which exists magneto-electric modulation can be realized by the embedded synthetic technology between cell atomic layers. Different from the natural materials with magnetic and electric properties, the "composite" means the compositional structure made by artificial design. However, currently, quantum functional oxide materials by artificial design still show weak magnetic and magnetoelectric coupling performances and cannot meet the demands of practical application for the quantum function devices. Therefore, seeking new quantum functional oxide materials is of great significance to expand quantum multi-functional material systems, strengthen the quantum multi-functional modulation, and find novel quantum coupling mechanisms.In this thesis, new quantum functional materials are synthesized and structural transformation induced by chemical substitution in such materials are studied, because that could give rise to intriguing physical phenomena and extraordinary coupling properties. This thesis mainly includes:1) studying the effects of the structural and physical properties of new layered quantum functional oxide material via the A/B-sites doping and understanding different physical mechanisms arising from the different element doping.2) Investigating structural transformation of the layered quantum functional oxide material and making structural modulation in such oxide when increasing excessive doping content; large effects (including ferroelectric, dielectric and ferromagnetic) were recorded at the analogous morphotropic transformation region (AMTR); the findings enrich the basic physics.3) Exploring the nanoscale structural evolution and the corresponding magnetic response in the inhomogeneous coexisted phase via adopting the minor Co-doping. In a word, these studies are helpful for understanding the knowledge of the new layered quantum functional oxide materials, and for providing the references for seeking more new quantum functional material systems.The contents of this thesis are as follows:In chapter 1, firstly, an overview of multiferroic materials and new quantum functional oxide materials; Secendly, recent progresses of new quantum functional oxide materials are introduced; At last, the main topics of this thesis are issued.In chapter 2, the effects of the structure and physical properties in six-layer Aurivillius-type homogeneous Bi7Fe3Ti3O21 by Gd substituting for Bi sites or Ni doping for Fe sites are discussed.In chapter 3, in order to understand the case of the structural transformation in details, structural evolution of the six-layer Bi7Fe3Ti3O21 and their physical properties when substituting excessive Co into Fe sites are investigated.In chapter 4, to figure out the process of the nanoscale structural evolution and the physical effect from the coexistence of two different phases, a mixed-layer Aurivillius-type multiferroic oxide, Bi11Fe3Ti6O33, is introduced. In addition, we also study the effect of magnetic property by Co doping for Fe sites in the mixed-layer phase.In chapter 5, we develop a comprehensive and reliable technique to detect and quantify the ferromagnetic inclusions in Aurivillius-phase multiferroic ceramics, which is named the derivative thermo-magneto-gravimetry (DTMG) technique.In chapter 6, we deliver the summary of the whole work in this thesis and an outlook for the related future work... |
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