Preparation and Characterization of PbTiO3-Ni(Fe2-xMnx)O4 Magnetoelectric Composites of Zero Thermal Expansion

• Main Authors: WANG, PO-HSUN, 王柏勛
• Other Authors: Ho, Chih-Sung
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/6gs4h2

碩士 === 東海大學 === 化學工程與材料工程學系 === 106 === Magnetoelectric composites possess ferromagnetism and ferroelectricity, which is a kind of multiferroic material. They have been applied in microwave equipment, sensors, transducers, and radio frequency identification (RFID). However, the higher performance, smaller size, and faster transport speed of the electronic products are required. The distance between the composite devices will be more intensive, which results in an increase in working temperature. The thermal expansion or contraction will seriously affect the performance of magnetoelectric composites, which may lead to failure or even damage. Therefore, zero thermal expansion have been one of the issues that must be faced. NiFe2O4 is an excellent ferromagnetic material with positive thermal expansion, which possesses high permeability and low magnetic loss characteristics. To achieve zero thermal expansion, PbTiO3 with a special key property, the negative thermal expansion (NTE), is selected as the ferroelectric material to combine with NiFe2O4. By adjusting the composition ratio of PbTiO3 and NiFe2O4, the magnetoelectric composites of zero thermal expansion can be reached. By doping a third element, the optimal performance of composite can be achieved. In this study, PbTiO3-NiFe2O4 magnetoelectric composites of zero thermal expansion with fixed proportion were prepared by solid state and sol-gel methods, respectively. The third element Mn of various amonts were doped into NFO, which became NFMO. PTO was combined with fixed proportion NFMO, which became PTO-NFMO. Composites were sintered for 3 hours at the temperature of 1096oC and 1015 oC in the atmospheric environment by solid state and sol-gel methods, respectively. The effects of different preparation methods of compsites on crystal structure, thermal expansion coefficients, relativee density, microstructures and magnetoelectric properties have been investigated. The XRD results showed that composites with various doping amounts of Mn all had perovskite and spinel structures which were same as those of pure PTO and NFO. Magnetoelectric composites which prepared by solid state method have zero thermal expansion at PTO : NFO = 1.1 : 1.0. The thermal expansion coefficients of composites prepared by solid state method increased with increasing doping amount of Mn. Magnetoelectric composites which prepared by sol-gel method have zero thermal expansion at PTO : NFO =12.0 : 1.0. The thermal expansion coefficients of composites prepared by sol-gel method decreased with increasing doping amount of Mn. The relative densitis of magnetoelectric composites were all above 50%. At the same doping amount of Mn, the relative densities of the composites prepared by solid state method were higher than those of the composites prepared by sol-gel method. S-PbTiO3-Ni(Fe1.985Mn0.015)O4 prepared by solid state method has the highest densities 5.27 g/cm3 and relative densities 77.46%, respectively. The microstructures of composites were observed by using SEM at magnifications of 200, 3000, and 10000X. Large grains were NFMO and small grains are PTO in the composites which were proved by EDS. The voids of composites prepared by sol-gel method were larger than those of composites made by solid state method. When the doping amount of Mn increased, the NFMO grain possessed edges and corners. Dielectric constant and dielectric loss were measured by using net work analyzer at frequencies of 7.0 GHz. The s-PbTiO3-Ni(Fe1.925Mn0.075)O4 had a maximum dielectric constant of 18.28 and the g-PbTiO3-Ni(Fe1.955Mn0.045)O4 had a minimum dielectric loss of 0.001. Permeability and permeability loss were measured by using net work analyzer at frequencies of 7.5 GHz. The s-PbTiO3-Ni(Fe1.925Mn0.075)O4 had a maximum permeability of 21.88 and the g-PbTiO3-Ni(Fe1.955Mn0.045)O4 had a minimum permeability loss.