Synthesis of a Magnetic-Dielectric YIG@BaTiO 3 Composite via Hydrothermal Processing
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0962-P10-20
Synthesis of a Magnetic-Dielectric YIG@BaTiO3 Composite via Hydrothermal Processing Shin-Wei Lin, Wen-Song Ko, and Mean-Jue Tung Material and Chemical Research Laboratories, Industrial Technology Research Institute, Rm. 302, Bldg. 77, 195 Sec. 4, Chung Hsing Rd., Hsinchu, 310, Taiwan
ABSTRACT YIG@BaTiO3 composite is synthesized by a sequential process involving the formation of TiO2 by sol-gel reaction and a subsequent hydrothermal transformation from TiO2 to BaTiO3. TiO2 layer was coated on YIG particle via sol-gel reaction which comprised hydrolysis and condensation reaction of titanium n-butoxide. The pH value of the solution was precisely controlled to ensure that YIG particles could be well dispersed in the solution and the concentrations of TBOT and H2O were adjusted to obtain variant thickness of TiO2 layer. Nanosized BaTiO3 coating on YIG was achieved by hydrothermal conversion of the TiO2 shell layer. Magnetic properties of YIG@BaTiO3 composites were investigated by vibrating sample magnetometer. Coercivity of YIG@BaTiO3 composites with different composition are not affected but the saturated magnetization drop down with increasing of the volume ratio of BaTiO3. Permittivity of YIG is raised by coating of BaTiO3 layer and varies from 6 to 60 and 75 by tuning up the volume ratio of BaTiO3 in the composite. The mechanism of the formation of YIG@BaTiO3 composite is also discussed in the article. INTRODUCTION Yttrium iron garnet (YIG) is extensively studied owing to its ferrimagnetic nature and is widely used in various microwave and optical-communication devices like circulator, oscillator, phase shifter and magnetic bubble domain-type digital memories [1-3]. Besides, YIG is also used as a host material for the synthesis of YAG solid-state laser. However, lower permittivity of YIG restricts its application in microwave frequency. To improve the dielectric property of YIG, BaTiO3 was introduced to incorporate with YIG particle to enhance overall permittivity. In the past, BaTiO3 has been prepared by a high temperature solid state reaction involving the interaction of barium carbonate and titanium oxide at temperature over 900ºC. Nevertheless, the ceramic method has several disadvantages like coarser particle size, poor compositional control and contaminations during the step of grinding. So as to overcome the problems arising from the method, lots of wet chemical methods were utilized. In the recent years, wet chemical methods such as precipitation, gas condensation and sol-gel processing [4-7] are developed to improve the purity and homogeneity, but these methods all have their shortcomings. Besides the techniques mentioned above, hydrothermal processing [8-10] offers a potential way to prepare nano-sized, pure BaTiO3 particles by using an aqueous medium under low temperature (< 250ºC). In this paper, we use a two-steps method which includes sol-gel reaction of TiO2 and hydrothermal reaction of BaTiO3 to synthesize the desired core-shell YIG@BaTiO3 composite. The permittivity of YIG is raised by
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