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

Abstract

Here we report on the synthesis and phase formation of perovskite 0.75 Pb(Zn-1/3,Nb-2/3)O-3-0.25 BaTiO3 (PZN-BT) by means of a new aqueous solution-gel method. The gelation process was optimized for an ammonium PZN acetate citrate precursor. The chemical homogeneity of this precursor was investigated by means of TEM-EDX analysis (Transmission Electron Microscopy-Energy Dispersive X-ray analysis). All metal ions were found to be homogeneously dispersed in the precursor gel at least down to 10 nm. An aqueous BaTiO3 precursor was synthesized and its oxide formation was investigated by means of HT-XRD (High Temperature X-ray Diffraction) and TGA-MS (Thermogravimetric Analysis 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 precursor if proper thermal treatment is applied (14 minutes sintering at 800 degreesC after fast firing at 50 degreesC min(-1)). Finally a phase formation mechanism 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 the perovskite decomposes irreversibly into that same pyrochlore together with volatile PbO and ZnO. The evolution of PbO was proved with TGA.