Processing and dielectric properties of the mixed-layer bismuth titanate niobate Bi7Ti4NbO21 by the metal-organic precursor synthesis method

The preparation of homogeneous Bi7Ti4NbO21 Single phase nanosized ceramic p owders at temperatures as low as 400-500 degreesC using a metal-citrate com plexes method, based on the Pechini-type reaction route, is described. The thermal decomposition/oxidation of the polymerized resin, as investigated b y TG/DTA, XRD, Raman spectroscopy and SEM, led to the formation of a well d efined orthorhombic Bi7Ti4NbO21 compound with lattice parameters a = 0.544, b = 0.540 and c = 2.905 +/- 0.0005 nm. Reaction formation takes place thro ugh an intermediate binary phase with a stoichiometry close to Bi20TiO32 wh ich forms between 300 and 375 degreesC. The metal-organic precursor synthes is method, allows the control of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of the nanosized bismuth titanate niobate, Bi7Ti4NbO 21, ceramic powders, at temperatures much lower than usually needed in the conventional route. Sintering of the as-prepared ceramic powders led to nea r full density samples in the temperature range 1100-1130 degreesC. The mix ed-layer structure Bi7Ti4NbO21 ceramics showed two phase transitions at abo ut 650 and 850 +/- 5 degreesC, and a piezoelectric modulus, d(33), as high as 20x10(-12) C/N. (C) 2000 Elsevier Science Ltd. All rights reserved.