Phase formation of ferroelectric perovskite 0.75 Pb(Zn-1/3,Nb-2/3)O-3-0.25BaTiO3 prepared by aqueous solution-gel chemistry

Here we report on the synthesis and phase formation of perovskite 0.75 Pb(Z n-1/3,Nb-2/3)O-3-0.25 BaTiO3 (PZN-BT) by means of a new aqueous solution-ge l method. The gelation process was optimized for an ammonium PZN acetate ci trate precursor. The chemical homogeneity of this precursor was investigate d by means of TEM-EDX analysis (Transmission Electron Microscopy-Energy Dis persive X-ray analysis). All metal ions were found to be homogeneously disp ersed in the precursor gel at least down to 10 nm. An aqueous BaTiO3 precur sor was synthesized and its oxide formation was investigated by means of HT -XRD (High Temperature X-ray Diffraction) and TGA-MS (Thermogravimetric Ana lysis on-line coupled to Mass Spectrometry). The gel-to-oxide transition of the PZN-BT precursor was studied using HT-XRD and TGA-MS. It was concluded that 96+ weight% perovskite PZN-BT could be formed out of the gel precurso r if proper thermal treatment is applied (14 minutes sintering at 800 degre esC after fast firing at 50 degreesC min(-1)). Finally a phase formation me chanism for perovskite PZN-BT is proposed: perovskite 0.75 Pb(Zn-1/3,Nb-2/3 )O-3-0.25 BaTiO3 is formed out of a cubic pyrochlore PZN. At 850 degreesC t he perovskite decomposes irreversibly into that same pyrochlore together wi th volatile PbO and ZnO. The evolution of PbO was proved with TGA.