Ta doped alkali niobate, K(1-x)Na(x)Nb(1-y)TayO(3) (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 super-critical water flow system. The syntheses were carried out at temperatures from 400 to 480 degrees 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 degrees 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 K0.5Na0.5Nb0.7Ta0.3O3 was obtained from the precursor composition with initial Nal(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 degrees C) and moderate pressures (ca. 25-30 MPa), and was formed at 420 degrees C, 25 MPa where the density of water was less than 150 kg m(-3). The ferroelectric property of KNNT particles sintered at 1085 degrees C was determined to be 96.0 pC/N. 2016 Elsevier B.V. All rights reserved.