EFFECT OF AL2O3 AND BI2O3 ON THE FORMATION MECHANISM OF SN-DOPED BA2TI9O20

High-performance Ba2Ti9O20 ceramics are attracting great attention, bu t their formation mechanism still is somewhat unclear. The present inv estigation shows that the formation of Ba2Ti9O20 can be promoted strik ingly by the participation of Bi2O3 and Al2O3. The effect of Bi2O3 on the formation of Ba2Ti9O20 is attributed to the fact that migration of the involved reactants is accelerated by liquid which forms from the melting of Bi2O3 above 830-degrees-C. This migration, however, is not the only rate-limiting factor. A high potential-energy barrier, result ing from stress that arises along the crystal-structured layers, also heavily restricts the formation of Ba2Ti9O20. The participation of Al2 O3, on the other hand, can reduce the height of this potential-energy barrier and effectively improve the kinetics of the formation of Ba2Ti 9O20 by causing the formation of BaAl2Ti6O16 crystals; these crystals intergrow with Ba2Ti9O20 crystals and result in decreased stress.