Solvothermal synthesis of nanocrystalline KTaO3: Effect of solvent dielectric constant

A set of KTaO3 nanopowders has been prepared at T = 180 degrees C using various aliphatic alcohols and water as solvents. Pronounced connection between the solvent type and potassium tantalate structures was found. Structural X-ray, TEM and Raman scattering experiments have shown that the solvent dielectric constant epsilon is an important critical parameter. At E 24 the cubic perovskite-type phase was formed. Mixed perovskite and pyrochlore phases were formed at larger values of epsilon. Only pure pyrochlore phase is realized when epsilon similar to 80. Pyrochlore-free perovskite-structure nanopowder phase formation with the particle size of similar to 18 and 28 nm was achieved when ethanol and isopropanol solvents were used. Under annealing the coherent domain size decreased down to 6 and 18 nm respectively, since the amorphous phase crystallized. Crystallinity of both as-prepared and annealed powder is the best when isopropanol solvent is used. (C) 2012 Elsevier Ltd. All rights reserved.