Mechanism of Grain Orientation During Hot‐Pressing of Bismuth Titanate

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Abstract
Grain‐oriented Bi4Ti3O12 ceramics have been prepared by hot‐pressing. Platelike grains align during hot‐pressing; the long‐axis direction perpendicular to the crystal c axis is oriented perpendicular to the pressing direction. The effects of hotpressing conditions such as temperature, pressure, time, and type of filler on the density, orientation degree, and deformation of hot‐pressed compacts were examined. Sharp increases in the density, deformation, and grain orientation occurred during the early stage; the density decreased, and the latter two incresed on prolonged hot‐pressing. The grain orientation is closely related to the deformation in the radial direction. The grain‐orientation mechanism is discussed referring to mechanisms proposed for high‐temperature deformation in ceramics. The compact is deformed by two processes: one accompaines grain orientation, and the other does not. Grain‐boundary sliding is proposed for the former process. The contribution of grain‐boundary sliding to the deformation increases with increasing temperature and pressure. The filler also influences the contribution. The decrease in density is caused by cavity formation during prolonged hot‐pressing.

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