Dielectric Properties of BaTiO 3 Based Ceramics Prepared from Nano-powders
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Dielectric Properties of BaTiO3 Based Ceramics Prepared from Nano-powders Xiao-Hui Wang, Ren-Zheng Chen, Zhi-Lun Gui, Long-Tu Li State Key Lab of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing, 100084, P. R. China Email: [email protected]
ABSTRACT In this paper, the BaTiO3 nanoceramics have been fabricated by pressureless sintering for the first time. High purity BaTiO3 powders in nano-size of 50~80nm synthesized by wet chemical method were used to fabricate nanoceramics. The addition of an appropriate amount of Nb2O5 and Co3O4 was found to suppress the grain growth, which is normally encountered in the conventional pressless sintering. The effects of Nb2O5 and Co3O4 on the phase structure, microstructure and dielectric properties of the sintered ceramics were investigated. The BaTiO3 ceramics with the average grain size less than 100nm were achieved after sintering below 1220oC with dielectric constant up to 2000 at room temperature, which is of cubic structure and meets the requirement of X7R specification.
INTRODUCTION There is a continuous drive to reduce component size and this can only be achieved by (i) increasing relative permittivity of the dielectric and (ii) reducing the thickness of the ceramic layer in the MLCC. In response to the demand for small grain size in thinner dielectric layers of MLCC, nano-scale BaTiO3 powders are required [1]. There are some papers concerning about the preparation of nano-sized BaTiO3 powders and their unique properties originated from the size effect [2, 3]. But, still now there has been few papers reported about nano-grained BaTiO3 ceramics, because it is difficult to obtained nano-grained ceramic due to the grain growth during sintering. How to control the grain growth and prepare nano-grained BaTiO3 ceramic is still a challenge. In this paper, Nb2O5 and Co3O4 were introduced into nanopowders of BaTiO3 as dopants, the effects of the dopants on the sintering behavior and the properties of BaTiO3 ceramics were investigated.
EXPERIMENTAL DETAILS The nano-sized powders of BaTiO3 were synthesized by wet chemical method—oxalate precipitation method [4-6]. The starting materials used in this study were barium acetate
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(Ba(CH3COO)2), tetrabutyl titanate (Ti(OC4H9)4), oxalic acid (H2C2O4) as precipitator and alcohol as a media solution. First, the oxalic acid was dissolved in alcohol, and tetrabutyl titanate was added into it with constant stirring to form a transparent yellow solution (H2TiO(C2O4)2). After that, the barium acetate solution were mixed with the above solution, ultrafine oxalate precipitate (BaTiO(C2O4)2â‹…4H2O) was obtained. The mole ratio of barium acetate, tetrabutyl titanate and oxalic acid used here was 1:1:2.2. The precursor was then dried and calcined at 800oC~1050oC for 2h to produce pure BaTiO3 powders. The crystalline structures were investigated using X-ray diffraction (XRD) and the grain sizes were determined by transmission electron microscopy (TEM). In order to prepare
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