Effect of Ta substitution on the synthesis of (K,Na)(Nb,Ta)O3 powders by hydrothermal reaction: Insight into the combination of alkaline solution and raw powder

Shintaro Sano, Takahisa Shiraishi, Takanori Kiguchi, Toyohiko J. Konno

Research output: Contribution to journalArticlepeer-review

Abstract

Ta substituted (K,Na)NbO3 powders with K-rich composition across polymorphic phase boundary were synthesized at 200 °C by hydrothermal method. The amount of Ta content in the powders was controlled by changing the nominal composition of raw powders, C = [Ta2O5]/([Nb2O5] + [Ta2O5]). Elemental mappings using a transmission electron microscope showed all the elements (K, Na, Nb, and Ta) were contained in the powders. X-ray diffraction measurement showed that (K,Na)(Nb,Ta)O3 solid solution powders can be obtained for all nominal compositions (C = 01), and that the orthorhombic-tetragonal phase transition can be induced by controlling C value, yet the diffraction peaks arising from a secondary phase were also detected in the range of C = 0.51. Scanning electron microscopy (SEM) observation revealed that the morphology of powder changed from polymorphic to square, and the size of the square-shaped (K,Na)(Nb,Ta)O3 powder decreased, with increasing the nominal composition. Temporal evolution of the emerged phases revealed that the range of intermediate phase became shorter with increasing the nominal composition, allowing the perovskite phase to form from early stages. In addition, the cause of the secondary phase was unreacted raw powder. Observations on the powder synthesis with end-member composition (KOHNb2O5, NaOHNb2O5, KOHTa2O5, and NaOHTa2O5) has shown that perovskite single-phase was formed in KOH-Nb2O5, NaOH-Nb2O5, and KOH-Ta2O5, while that unreacted raw powder was detected in the combination of NaOH and Ta2O5. These results demonstrated that Ta substitution is an effective way to control the morphology of powder and that the synthesis behavior of (K,Na)(Nb,Ta)O3 is strongly dependent on the combination of alkaline solution and raw powder.

Original languageEnglish
Pages (from-to)365-371
Number of pages7
JournalJournal of the Ceramic Society of Japan
Volume129
Issue number7
DOIs
Publication statusPublished - 2021 Jul 1

Keywords

  • (KNa)(Nb Ta)O powders
  • Crystal structure
  • Hydrothermal synthesis
  • Microstructure
  • Synthesis behavior

ASJC Scopus subject areas

  • Ceramics and Composites
  • Chemistry(all)
  • Condensed Matter Physics
  • Materials Chemistry

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