Abstract
The pre-reaction step, which is the holding time at 1000 °C in reaction-sintering process, was observed to influence the characteristics of the Ba 2 Ti 9 O 20 materials profoundly. For the materials possessing high sintered density and of pure Hollandite-like structure, the uniformity of granular structure is the prime factor, altering the microwave dielectric properties of the samples. Utilizing the BaTi 4 O 9 + BaTi 5 O 11 mixtures to replace for the 2BaTiO 3 + 7TiO 2 ones pronouncedly improved the uniformity of the microstructure and thus markedly increased the Q × f-value for the Ba 2 Ti 9 O 20 materials. The possible explanation for such a phenomenon is that the B-series mixture forms the Ba 2 Ti 9 O 20 Hollandite-like phase in a simpler way and results in more uniform microstructure then the A-series mixture. The microwave properties of B-series materials are superior to those of A-series ones, achieving K = 38.2 and Q × f-value = 36,000 GHz for the samples, which were pre-reacted at 1000 °C for 6 h and were sintered at 1410 °C for 4 h by reaction-sintering processes. © 2009 Elsevier Ltd. All rights reserved.