A road to environmentally friendly materials chemistry: low-temperature synthesis of nanosized K0.5Na0.5NbO3 powders through peroxide intermediates in water

Abstract

In the framework of research devoted to development of new synthetic methods for alkali niobates with emphasis on the principles of green chemistry, the first example of the efficient synthesis of K_0.5Na_0.5NbO₃ powders from pure aqueous solution under normal reaction conditions is presented. Aqueous solutions of stable Nb(V)–peroxo–citrate at pH 8.50 or Nb(V)–peroxo–glycine at pH 5.50 chelate complexes were prepared, characterized and studied with FT-IR and UV-Vis spectroscopy. The addition of sodium and potassium acetates or nitrates led to the final aqueous precursor solution and it was shown that single phase K_0.5Na_0.5NbO₃ nanopowders could be obtained by simple calcination of these peroxide intermediates at the desired, relatively low temperature (500–550 °C). The results showed that the particle size and morphology, analysed by FE-SEM, strongly depended on the type of Nb(V)–peroxo precursor and the annealing temperature. K_0.5Na_0.5NbO₃ particles prepared through the Nb(V)–peroxo-citrate precursor resulted in the formation of sharp-edged nanocuboids in the size range 50–200 nm, while the synthetic route through the Nb(V)–peroxo–glycine precursor surprisingly also enabled formation of particles with rod-like morphology.