Preparation of textured bismuth titanate ceramics through templated grain growth combined with spark plasma sintering
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Preparation of textured bismuth titanate ceramics through templated grain growth combined with spark plasma sintering Keishi Nishio1, Rena Maeda1, Junsuke Kihou1, Yasuo Kogo1, Tohru Kineri2 and Atsuo Yasumori1 1 Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan 2 Department of Materials Science & Environmental Engineering, Tokyo University of Science, Yamaguchi, 1-1-1 Daigaku-doori, Onoda-shi, Yamaguchi, 756-0884,
ABSTRACT Textured bismuth titanate (Bi4Ti3O12), the simplest and best known compound among the bismuth layer-structure ferroelectrics is interesting because of its peculiar switching behavior which results from a small c-axis component of the spontaneous polarization and a small coercive force. We prepared Bi4Ti3O12 ceramics through the templated grain growth (TGG) method combined with the spark plasma sintering (SPS) method. The TGG method was developed to provide a simpler way of creating textured ceramic microstructures. The SPS method enables a compact powder to be sintered under uniform heating to a high density at relative low temperatures and with much shorter sintering periods than with conventional sintering. We obtained a Bi4Ti3O12 precursor powder through a co-precipitation method with Ti alkoxide and Bi oxide as raw materials. Platelet Bi4Ti3O12 was synthesized from the precursor powder through a flux method using NaCl and KCl. The obtained platelet Bi4Ti3O12 had a high aspect ratio. The ceramics were prepared by SPS treatment using a mixture of the platelet Bi4Ti3O12 and the amorphous precursor powder. As a result, dense ceramics could be easily obtained without crystalline amorphous precursors and grain growth was not observed during the sintering. After heat treatment of the ceramics, we obtained highly textured, high density Bi4Ti3O12 ceramics. The ceramics showed high orientation, above 70%, for the c-axis direction and high density of over 85%.
INTRODUCTION Bismuth layer-structure ferroelectrics (BLSFs) in the system (Bi2O2)2+(An-1BnO3n-1)2- (n=1 to 5) have a structure in which the (Bi2O2)2+ layers and quasi-perovskite units are piled up along the crystallographic c-axis [1-6]. BLSFs are suitable materials for application in high-temperature transducers and capacitors because of their high Curie temperature and high piezoelectric coefficient. Bismuth titanate (Bi4Ti3O12) is a well-known member of the BLSF family [7-9]. Its structure consists of three quasi-perovskite units sandwiched between bismuth oxide layers. In addition, Bi4Ti3O12 is an excellent material for a templated grain growth (TGG) study because it is easily obtained as a platelet particle through the flux method, and it is a candidate for use in high-temperature piezoelectric devices because of its high Curie temperature. However, poling of the ceramics is difficult because low crystal symmetry inhibits the appropriate orientation of the polarization axis. Textured ceramics have been obtained through the tape casting method using TGG [10-13]
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