Phase stability of B₂O₃-added Ba₂Ti₉O₂₀ ceramic: Processing effects

Abstract

Preparation of dense and phase-pure Ba2Ti9O20 is generally difficult to achieve using solid-state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition. This study investigated the effects of B2O3 on the densification, microstructural evolution, and phase stability of Ba2Ti9O20. Samples from the host material (2BaO · 9TiO2) with and without the addition of 5 wt% B2O3 were prepared through different processing routes. For the pure host material sintered at temperatures ranging from 800 to 1100 °C, the reaction products followed the sequence of BaTi2O5 → BaTi4O9 → BaTi5O11 → Ba2Ti9O20. The phase transformation proceeded faster in the bulk compared to the free surface of the sample. BaTi5O11 and BaTi4O9 with a minor amount of Ba2Ti9O20 were found in the ground powder of ceramics sintered at 1100 °C. For the samples prepared from host material with the addition of 5 wt% B2O3, Ba2Ti9O20 started to form at temperatures as low as 800 °C. The sequence of reaction products followed Ba4Ti13O30 → BaTi4O9 → BaTi5O11 → Ba2Ti9O20. Sintering at above 1000 °C yielded pure Ba2Ti9O20 phase, suggesting the effective role of B2O3 on the phase stability of Ba2Ti9O20. It was found that precalcination of host material before the addition of B2O3 gives an additional benefit to the Ba2Ti9O20 formation. Crystallization of pure Ba2Ti9O20 phase was completed at a sintering temperature as low as 900 °C without any solid solution additive such as SnO2 or ZrO2, due to the fact that the phase transformation of the samples began with BaTi4O9 and BaTi5O11 during sintering. Also, B2O3 was found to be unstable during the high-temperature sintering at 1200 °C, and the results are discussed.

Low-temperature sintering and microwave dielectric characteristics of Ba2Ti9O20 ceramics

“…In the case of the specimen sintered at 800 • C with BaB 2 O 4 addition, no considerable change in phase evolution was observed when compared with the calcined powders. However, as the sintering temperature increased, the dominant BaTi 4 O 9 phase produced at the low sintering temperature of 800 • C disappeared and the Ba 2 Ti 9 O 20 phase was mainly obtained with a minor amount of BaTi(BO 3 shown in Fig. 3.…”

“…Several studies have shown that the addition of B 2 O 3 has the advantages of lowering sintering temperatures and improving dielectric properties of Ba 2 Ti 9 O 20 . 3,4 It was also reported that B 2 O 3 addition could enhance the formation of Ba 2 Ti 9 O 20 . However, chemical reaction between the glass and ceramics should be considered because reaction induced compositional change or development of second phases might deteriorate the dielectric properties.…”

Effect of lithium-based glass addition on the microwave dielectric properties of Ca[(Li1/3Nb2/3)1−xTix]O3−δ ceramics for LTCC applications

“…Recent research trend suggests that glass addition is a useful method of producing low loss ceramics like (Zr,Sn)TiO 4 , Ba 2 Ti 9 O 20 , Ba(Mg 1/3 Ta 2/3 )O 3 , Ca 5 Nb 2 TiO 12 , BaTi 4 O 9 , 0.83ZnAl 2 O 4 -0.17TiO 2 , Mg 2 SiO 4 , etc. at low sintering temperatures [10][11][12][13][14][15][16][17][18][19][20][21]. However, majority of ceramic-glass systems offer relatively inferior dielectric properties compared to those of high temperature firing systems.…”

Tailoring the Microwave Dielectric Properties of Ca5Ta2TiO12 Ceramics Through Glass Addition

“…The complex procedures involved, the high cost of the chemicals, and poor microwave dielectric properties preclude the use of chemical synthesis for the industrial production of DRs 25 . Recent researches suggest that the addition of glassy materials as sintering aids is the most effective and simple method available to attain the above‐mentioned goals, as has been experimentally shown with low loss DR materials like (Zr, Sn)TiO 4 26,6 Ba 2 Ti 9 O 20 , 27–29 BaTiO 4 , 30–32 (Mg 0.5 Ca 0.5 )TiO 3 , 33–35 BiNbO 4 , 36 and Ba(Mg 1/3 Ta 2/3 )O 3 37–39 . However, for most of the systems with a higher amount of glass or a mixture of additives, the reduction of sintering temperature is usually accompanied by an abrupt decrease of physical and dielectric properties of the matrix material because of the formation of secondary phases 40 .…”