Low-temperature synthesis of bismuth titanate niobate (Bi7Ti4NbO21) nanoparticles from a metal-organic polymeric precursor

This paper describes the preparation of homogeneous Bi7Ti4NbO21 single-phase ceramic powders of similar to 55 nm crystallite size, at temperatures as low as 400 degrees-500 degrees C using a metal citrate complex method based on the Pechini-type reaction route. The thermal decomposition/oxidation of the polymerized resin, as investigated by TG/DTA, XRD, and SEM, led to the formation of a well-defined orthorhombic Bi7Ti4NbO21 compound with lattice parameters a = 0.544, b = 0.540, and c = 2.905 +/- 0.0005 nm. Reaction takes place through an intermediate binary phase with a stoichiometry close to Bi20TiO32 which forms between 300 degrees and 375 degrees C. The metalorganic precursor synthesis method, where Bi, Ti, and Nb ions are first chelated to form metal complexes and then polymerized to give a gel, allows control of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of nanosized bismuth titanate niobate (Bi7Ti4NbO21) ceramic powders, at temperatures much lower than usually needed by conventional processing of mixed-oxide powders.