Solvothermal synthesis of nanocrystalline KTaO3: Effect of solvent dielectric constant

A set of KTaO3 nanopowders has been prepared at T = 180 °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 ɛ is an important critical parameter. At ɛ ∼ 24 the cubic perovskite-type phase was formed. Mixed perovskite and pyrochlore phases were formed at larger values of ɛ. Only pure pyrochlore phase is realized when ɛ ∼ 80. Pyrochlore-free perovskite-structure nanopowder phase formation with the particle size of ∼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.