Synthesis of ferroelectric K1-xNaxNb1-yTayO3 nanoparticles using a supercritical water flow system

Keisuke Okada, Hiromichi Hayashi, Masafumi Takesue, Masaru Watanabe, Richard L. Smith

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4 Citations (Scopus)


Ta doped alkali niobate, K1-xNaxNb1-yTayO3(KNNT) nanoparticles (ca. 60–80 nm) were continuously synthesized from Nb/Ta-sol with polyacrylic acid as a dispersant and NaOH/KOH solutions using a supercritical water flow system. The syntheses were carried out at temperatures from 400 to 480 °C, at pressures from 25 to 30 MPa, and at reaction times from 0.5 to 8 s. Single phase KNNT was obtained at 480 °C and 25 MPa for which the Na/(Na + K) and Ta/(Ta + Nb) molar ratios of the products increased with an increase in the precursor molar ratios with slopes of 2.7 and 1.0 for Na/(Na + K) and Ta/(Ta + Nb), respectively. Single phase K0.5Na0.5Nb0.7Ta0.3O3was obtained from the precursor composition with initial Na/(Na + K) and Ta/(Ta + Nb) molar ratios of 0.19 and 0.3, respectively. Crystallinity increased with an increase in the reaction time and the particles formed at 0.5 s were spherical-shaped and they were cube-shaped at the longer reaction times. Single KNNT phase was predominantly produced at high temperatures (ca. 420–480 °C) and moderate pressures (ca. 25–30 MPa), and was formed at 420 °C, 25 MPa where the density of water was less than 150 kg m−3. The ferroelectric property of KNNT particles sintered at 1085 °C was determined to be 96.0 pC/N.

Original languageEnglish
Pages (from-to)101-108
Number of pages8
JournalJournal of Supercritical Fluids
Publication statusPublished - 2017


  • Alkali tantalate niobate
  • Hydrothermal reaction
  • Lead-free materials
  • Supercritical fluid

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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