Tuning of electrical and magnetic properties in nanocomposites of conductive LaNiO3 and transition metal oxides

Abstract

The discovery of new composites by integrating materials of different physical properties with optimal control is of immense interest to researchers at present. Today, there are several composites being used for several applications. The list of composites and their applications is endless from toys to space applications in today's life, as it is a very broad area of research. Composites are made up of the combinations of two or more materials in which one of the materials, so called reinforcing phase in the form of fibers, tubes and particles which are incorporated in the other called matrix phase. The main functions of the matrix are to transfer the stresses between the reinforcing fibers or particles, and to protect them from the mechanical and environmental damage. This enhances their mechanical properties like strength and stiffness. A composite is therefore one synergistic combination of two or more phases which is superior to their individual phases due to more physical and chemical properties. Ceramic composites have successfully replaced many traditional ceramics and metals in several applications due to their light weight and high strength, high tensile strength at elevated temperatures, high creep strength and toughness. Typically, composites can be properly designed and manufactured, by the appropriate combination of the strength of the reinforcing phase and the toughness of the matrix. Such ceramic composites can be more capable to give the desirable properties, which is not possible with a single conventional ceramic. Polymer matrix composites and metal matrix composites have a large number of applications in many fields. However, there are certain issues such as homogeneity of fillers (particles or fibers), recycling, lack of stability, low mechanical and thermal strength, very high coefficient of thermal expansion, etc. The disadvantages of these composites are the difficulty in the production of fiberreinforced composites and their increased labor cost. Ceramic matrix composites are more significant over single phase ceramics, metals matrix and polymer matrix composites in some applications due to their high fracture toughness and high resistant to thermal shocks. They are used in the field of automotive industry, renewable or alternative energies, healthcare, electronics and telecommunications, aerospace, gas sensors and in many high temperature applications. These are based on the combination of physical properties and are referred to as bio-ceramics, electroceramics, magneto˗ceramics, opto˗ceramic, multiferroics and catalysts, etc. Several materials like carbon, graphene and metal oxides have been used to produce composites with different combinations to get superior physical properties. In the present work, the conducting and magnetic metal oxide mixtures were preparation and examined as metal oxide composites. The electrically conductive lanthanum nickelate (LNO) was prepared as the conducting matrix. Ferrites of spinel cubic structure like CoFe2O4, Ni Fe2O4 and barium hexaferrite BaFe12O19 were prepared as magnetic phase. The synthesis, structural, morphological and compositional studies of lanthanum nickelate (LaNiO3) and Co, Ni, Ba ferrites were carried out. The electrical conductivity of LaNiO3 and the magnetic properties of ferrites were investigated at room temperature. Three nanocomposite systems of LaNiO3 with different ferrites were prepared. All composites were investigated for their structural, morphological and compositional studies. The electrical and magnetic properties of composites were investigated. The study of these composites was further extended for electromagnetic interference (EMI) shielding to test shielding effectiveness. The main results on electrical conductivity, magnetic properties and EMI shielding of nanocomposites are briefly summarized. In the thesis, major findings on this work are discussed. The composites of conducting and magnetic metal oxides have not yet been studied and reported. The electrical and magnetic properties of composite materials can be finely tuned by varying concentration of reinforcing phase into conducting matrix and these materials are explored in order to search possible application. This work mainly focuses on the i) Preparation of new composites using conductive and magnetic metal oxides, ii) Tuning of electrical conductivity and magnetic properties, iii) To study composites for EMI shielding, iv) To check the possibilities of applications in the field of electronics and v) To explore the surface and interface physics of hetero structure. Electromagnetic interference (EMI) is a fast growing problem in the modern era of electronics, telecommunication and in various instruments. It has become a critical area to be considered in electronic design and packaging. The increasing usage of large number of electronic devices and the need of increasing processor frequencies, the environment is becoming noisy due to the increasing electromagnetic fields. Therefore, it is necessary to prevent the unwanted EM waves with the adequate EMI shielding. The desire of high performance shields with the reduction in size, weight and price had been a great interest of researchers to discover new materials as suitable candidate for electronic housing. Presently, there are several types of housings and EMI shields are made up of polymer composites and thin metal or metal-alloy sheets work to protect devices from electromagnetic waves. As a part of present thesis work, we have studied all above composites for the EMI shielding measurements in the frequency range of 8 to 18 GHz. It is observed that each composite system showed a very high shielding effectiveness.