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

This paper describes the preparation of homogeneous Bi7Ti4NbO21 single-phas e 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 tak es place through an intermediate binary phase with a stoichiometry close to Bi20TiO32 which forms between 300 degrees and 375 degrees C. The metalorga nic precursor synthesis method, where Bi, Ti, and Nb ions are first chelate d to form metal complexes and then polymerized to give a gel, allows contro l of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of na nosized bismuth titanate niobate (Bi7Ti4NbO21) ceramic powders, at temperat ures much lower than usually needed by conventional processing of mixed-oxi de powders.