Structural Transformation of Hexagonal (0001)BaTiO3 Ceramics to Tetragonal (111)BaTiO3 Ceramics

A ceramic slurry that contains a 6H-type Ba(Ti0.95Mn0.05)O-3 powder was casted into a plaster mold under 10 T magnetic field to form a green compact of (0001)-oriented Ba(Ti0.95Mn0.05)O-3. After sintering the green compact at 1300 degrees C in air, it was confirmed that the (0001)-oriented 6H-type perovskite structure transformed to a (111)-oriented 3C-type perovskite structure. The structural transformation was again examined using hexagonal BaTiO3 prepared by reducing pseudo-cubic BaTiO3 powder in H-2 atmosphere. In this case, the preferred (0001) orientation was not confirmed for the green compacts. After sintering the green compacts at 1300 degrees C in air, mixed crystal orientations of (100)/(001) and (111) were observed for the resultant tetragonal BaTiO3 ceramics. This (100)/(001) orientation was suppressed by annealing the hexagonal BaTiO3 powder at 1000 degrees C before slip-casting, leading to highly (111)-oriented ceramics. It was found that the green compacts of (0001)-oriented hexagonal BaTiO3 can transform into (111)-oriented tetragonal BaTiO3 ceramics, maintaining the macroscopic crystal orientations due to a similar atomic stacking along [0001] of 6H-type BaTiO3 and [111] of 3C-type BaTiO3. (C) 2011 The Japan Society of Applied Physics