Influences of pH on the structure, morphology and dielectric properties of bismuth titanate ceramics produced by a low-temperature self-combustion synthesis without an additional fuel agent

Bismuth titanate (BIT) ceramics were prepared by incorporating low-temperature self-combustion synthesis and pH modification. The pH value of the initial precursor was adjusted to 3, 5 and 7 by the addition of ammonium hydroxide (NH4OH) with different amount. The reaction between ammonium ions (NH4+) and nitrate ions (NO3−) induced the formation of ammonium nitrate (NH4NO3), in turn to favor the combustion by enhancing the decomposition rate. Excessive hydroxyl ions (OH−) at higher pH value dominated the chelating of the metal carboxylate and the metal ions, resulting in a strong hybridization between bismuth (Bi) and oxygen (O), and also the suppression of the independent volatility of Bi and bismuth oxide (Bi2O3). Such conditions contributed to the formation of pure BIT via the low-temperature self-combustion synthesis without the use of an additional fuel agent. A BIT ceramic with high relative density (91.35%) that exhibited a high dielectric constant of ∼340 and a low dissipation factor ∼0.028 was obtained by the synthesis method at the neutral condition. Furthermore, it offers ability for the use in high temperature applications up to 675 °C.