Da Jeong Kim

A bismuth ferrite and barium titanate solid solution compound can achieve good piezoelectric properties with a high Curie temperature when fabricated with low-temperature sintering followed by a water-quenching process, with no complicated grain alignment processes performed. By adding the super-tetragonal bismuth gallium oxide to the compound, the piezoelectric properties are as good as those of lead zirconate titanate ceramics. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

By modification of the heat-treatment process to avoid the intermediate temperature range where secondary phases are easily formed in BiFeO3, piezoelectric properties were improved; the direct piezoelectric sensor coefficient d33 increased from 240 to 352 pC/N in 0.67BiFeO3–0.33BaTiO3 (BF33BT) ceramic and from 402 to 454 pC/N in 1 mol % BiGaO3-doped BF33BT (BG) ceramic with almost unchanged high Curie temperatures around 454 °C. To understand the effects of water quenching after sintering, eight different BF33BT ceramics were prepared by using different cooling routes together with furnace-cooled and water-quenched BG ceramic. Structural, ferroelectric, and piezoelectric properties of these ceramics were compared. All after-annealed BF33BT ceramics were compared with quenched ceramics. Physical properties of the after-annealed ceramics were similar to those of the furnace-cooled ceramic. It was confirmed that the overall duration of heat treatment in the second-phase-forming intermediate temperature range plays an important role in processing BF33BT ceramics without secondary phases or defects.

Spherical-shape melanin nanoparticles with good water-dispersibility were successfully synthesized by a simple oxidation polymerization of 3,4-dihydroxy-phenylalanin (DOPA) with <TEX>$KMnO_4$</TEX>. Similar features to those known from natural and synthetic melanin polymers were observed from prepared melanin nanoparticles by FT-IR, UV-Vis., and ESR spectroscopic methods. Their binding ability with several heavy metal ions from aqueous solution was quantitatively investigated, and the maximum binding capacities with melanin nanoparticles to lead, copper, and cadmium ions were obtained as 2.45, 2.17 and 1.88 mmol/g, respectively, which are much larger values than those reported from natural and synthetic melanin polymers. The large binding capacity and fast binding rate of melanin nanoparticles to metal ions can make them an excellent candidate for the remediation of contaminated water.