Investigation On Tape Casting Process Of BST-MgO Composite Ceramics With Low Sintering Temperature

Combined with the requirements in the field of LTCC technology, in this paper, MgO was added to the BST materials to improve the electrical properties of BST, and B2O3 and Li2CO3 was chosen as sintering aid. This paper aims to prepare BST-MgO microwave ferroelectric ceramic materials by tape casting. For this propose, The effects of the powder constituents, solvent, and dispersant on the tape casting were investigated,to choose the optimal solvent, and dispersant. Moreover, BST-MgO ceramic materials with lower sintering temperature were obtained by tape casting. The details are listed below:The azeotropic mixtures of toluene-ethanol, and methyl ethyl ketone (MEK)-ethanol, and zeotrpic mixture of xylene-ethanol (with a mass ratio of 5/5) were chosen as the solvent systems, respectively, to prepare BST-MgO suspensions, tape casting slurries and green tapes. The results show that when the MEK-ethanol mixture was chosen as the solvent, the suspension presents lower viscosity, and faster settling rate; and the tape casting slurries were well dispersed and more stable, exhibiting nearly Newtonian flow behavior and significantly lower viscosity. Besides, the microstructure of green tapes prepare by this slurry were dense and homogeneous. For this reason, the azeotropic mixture of MEK-ethanol was chosen as the optimal solvent system.The mixtures of MEK-ethanol with different ratio of MEK to ethanol were chosen as the solvent systems, respectively, to prepare BST-MgO suspensions, tape casting slurries and green tapes. Studies found that when the ratio of MEK to ethanol was 6/4 in the solvent, BST-MgO suspensions and the tape casting slurries were stable, with proper viscosity. Besides, the green tape prepared was dense.The azeotropic mixture of MEK-ethanol was used as solvent system, and prepared BST-MgO suspensions by different dispersants, such as phosphate ester, triolein, Polyethylene glycol 1540, polyvinyl butyral (PVB), etc. Studies demonstrated that when PVB was chosed as dispersant, the BST-MgO suspension can attain to the optimal dispersion state with Newtonian flow behavior and significantly lower viscosity by adjusting the content of the dispersant.The effects of the solid loading and the ratio of BST to MgO in powder on the suspension were investigated. The result showed that the viscosity of the slurries increased notably and that the content of PVB dispersant used when the suspension was stable increased firstly and then kept invariability as the the solid loading of the suspension inceeased. However, when the the solid loading was more than 60wt.%, the suspension can not reach to stable state. Besides,as the content of BST in powder increased, the content of PVB dispersant used when the suspension was stable increased due to the decrease of adsorbability of PVB to the surface of powders.The azeotropic mixture of MEK-ethanol was used as solvent system, and PVB was used as dispersant, to prepare BST-MgO tape casting slurries and BST-MgO ceramics by tape casting. The tape casting slurries was appropriate to tape cast, and the microstructure of the green tapes and ceramic samples was dense. Meanwhile, the permittivity and the dielectric loss of the ceramic samples at 1MHz was 91.22 and 0.8×10-3, respectively. Besides, the tunability is 7.72% under a DC field of 1.7kV/mm.