D. Wattanasiriwech*, S. Wattanasiriwech and U. Intatha Pages 1 - 8 ( 8 )
Aims: To propose a method of KBT synthesis at lower temperature to solve volatility of the components.
Background: Lead-based perovskite materials have long been employed in electroceramic industries due to their excellent piezoelectric, ferroelectric, and dielectric responses. The high toxicity of lead, however, leads to the replacement of the lead-based perovskite use in devices with more environmentally friendly materials. KBT powders are traditionally prepared by solid-state reaction via the calcinations of K2CO3,Bi2O3 and TiO2 at high temperature 10. The high temperature calcination process leads to serious particle agglomeration, grain growth and small surface area, which all decrease the activity of powder. Instability of the KBT ceramic according to its high volatility of its component ions at elevated temperatures was the main concern for the application feasibility11.
Objective: This work was aimed to present the simplified method so-called “sol-hydrothermal” for the synthesis of KBT nanoparticles. Microstructure and phase evolution of the nanoparticles were investigated in details.
Method: Sol-hydrothermal in potassium hydroxide (KOH) solution at 140 – 200 °C for 2-24 hrs.
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, a phase separation was observed. Suitable hydrothermal time was found to be between 6-12 hrs, above which phase separation was also observed. Increasing the KOH solution concentration from 10 to 12, 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 was obtained under the synthesis condition of 180 °C for 12 hrs 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, sublimation of K-containing component occurred as evident by appearance of Bi2O3 and Bi4Ti3O12 phases.
Conclusion: In summary, KBT nanoparticles have been successfully prepared by the simple sol-hydrothermal method in a basic solution at low temperatures. Synthesis temperature, time and KOH concentration were found to effect powder characteristic greatly. Increasing synthesis temperature was found to effect phase development while increasing synthesis time resulted in 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 degree. The optimum synthesis conditions were at 180 C for 24 hrs 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.
Sol-hydrothermal, potassium bismuth titanate, nanoparticles, sinterability, crystallization, tetragonality
Center of Innovative Materials for Sustainability, School of Science, Mae Fah Luang University, Chiangrai, 57100, Center of Innovative Materials for Sustainability, School of Science, Mae Fah Luang University, Chiangrai, 57100, Center of Innovative Materials for Sustainability, School of Science, Mae Fah Luang University, Chiangrai, 57100