The aqueous solution-gel synthesis of perovskite Pb(Zr1-x,Ti-x)O-3 (PZT)

Starting from a novel water-based Zr(IV)-peroxo-citrato solution, an entirely aqueous solution-gel synthesis of Pb(Zr-0.53,Ti-0.47)O-3 (PZT) was carried out. Because of the tendency of Zr4+-ions to hydrolyze and condensate extensively in water, the Zr4+-ions had to be chemically modified by reaction with hydrogen peroxide and citric acid in a two-step precursor synthesis. A transparent amorphous PZT gel precursor was obtained by evaporating the solvent (water). This resulted in a network of cross-linked ammonium-carboxylate bonds that holds Zr(IV)-peroxo-citrato, Ti(IV)-peroxo-citrato and Pb(II)-citrate complexes. By combining complementary thermal analysis techniques such as HT-DRIFT (high-temperature diffuse reflectance Fourier-transform infrared spectroscopy), TGA-MS (thermogravimetrical analysis online coupled to mass spectrometry) and DTA (differential thermal analysis) insight in the decomposition mechanism of the PZT gel was gained. Three major regions could be distinguished; consecutively the non-coordinative matrix surrounding the metal ion complexes, the precursor complexes and the remaining organic matrix are being decomposed. The phase formation of crystalline perovskite PZT was investigated in situ by means of HT-XRD (high-temperature X-ray diffraction). It shows that sublimation of PbO leads to the phase segregation of a Zr-rich PZT phase when a stoichiometric PZT precursor is used. Single phase perovskite PZT however can be obtained at low temperature (similar to 610 degrees C) when a 16 % lead excess is applied.