The Sol-hydrothermal Synthesis of Potassium Bismuth Titanate Nanoparticles

Abstract

Aims: To propose a method of KBT synthesis at a lower temperature to solve the volatility of the components. Background: Lead-based perovskite materials have long been employed in electroceramic industries due to their excellent piezoelectric, ferroelectric, and dielectric properties. The high toxicity of lead, however, leads to the replacement of the use of lead-based perovskite in devices with more environmentally friendly materials. KBT powders are traditionally prepared by solid-state reaction through the calcinations of K2CO3, Bi2O3 and TiO2 at high temperature. The high-temperature calcination process leads to serious particle agglomeration, grain growth and small surface area, which decrease the activity of the KBT powder. Instability of the KBT ceramic according to the high volatility of its component ions at elevated temperatures was the main concern for the application feasibility. Objective: This work was aimed to present the simplified method called “sol-hydrothermal” for the synthesis of KBT nanoparticles. Microstructure and phase evolution of the nanoparticles were investigated in detail. Method: The sol-hydrothermal method was performed in potassium hydroxide (KOH) solution at 140-200°C for 2-24 h. Result: The result showed that increasing hydrothermal temperatures from 140°C to 200°C, the crystal structure was changed from pseudo-cubic to tetragonal. At 200°C, phase separation was observed. Suitable hydrothermal time was found to be between 6-12 h, above which phase separation was also observed. Increasing the KOH solution concentration from 10 to 12 or 15 and finally, 20 M gave rise to greater KBT peak intensity, suggesting a more complete crystallization process when the concentration was increased. Tetragonal KBT nanoparticles with c/a ratio of 1.0620 were obtained under the synthesis condition of 180°C for 12 h in 20 M KOH solution. Sinterability of the synthesized KBT nano-particles was further investigated by varying the sintering temperatures from 1000°C to 1080°C; the highest relative density of 97% was obtained in the sample sintered at 1050°C. However, at this sintering temperature and beyond, the sublimation of the K-containing component occurred as evident by the appearance of Bi2O3 and Bi4Ti3O12 phases. Conclusion: In summary, KBT nanoparticles have been successfully prepared by the simple solhydrothermal method in a basic solution at low temperatures. Synthesis temperature, time and KOH concentration were found to affect the powder characteristics greatly. Increasing synthesis temperature was found to affect the phase development while increasing synthesis time resulted in the development of crystallinity of the KBT powder obtained. Increasing KOH concentration from 10 M to 20 M gave rise to different particle growth and agglomeration degrees. The optimum synthesis conditions were at 180°C for 24 h in 10 M KOH solution. At this condition, KBT powder with a uniform particle size distribution and tetragonal structure could be obtained. The synthesis powder showed excellent sinterability. Sintering at only 1020°C for 2 h gave rise to fine grain ceramics with 95% relative density. However, as potassium was prone to sublime, increasing sintering temperature to 1050°C and beyond resulted in K-deficient phases. Sintering of the KBT should be done in K-saturating atmosphere to suppress this sublimation.