Abstract
Ta doped alkali niobate, K1-xNaxNb1-yTayO3 (KNNT) nanoparticles (ca. 60–80nm) 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 30MPa, and at reaction times from 0.5 to 8s. Single phase KNNT was obtained at 480°C and 25MPa 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 K0.5Na0.5Nb0.7Ta0.3O3 was 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 0.5s 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. 25–30MPa), and was formed at 420°C, 25MPa where the density of water was less than 150kgm−3. The ferroelectric property of KNNT particles sintered at 1085°C was determined to be 96.0pC/N.
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