THE ISOELECTRIC CONDITIONS OF THE CONSTITUENTS OF THE COMPLEX OXIDE PB(ZR,TI)O3

The complex oxide of composition Pb1-xZr0.52Ti0.4803 (x=0, 0.025 or -0.01) was produced by the solid state reaction of the composite oxides PbO, ZrO2 and TiO2 at 900-degrees-C. The synthesized sample was at least two phase: tetragonal and rhombohedral. Free PbO was found in the lead-zirconate-titanate (PZT) sample when an excess of lead oxide was added to the reaction mixture. In order to determine the isoelectric conditions at the oxide/electrolyte interface, microelectrophoresis was applied to single oxides and to the complex oxide suspended in aqueous solutions of sodium chloride and of ammonium acetate in the pH range 3-12. Zirconium and titanium oxides exhibited isoelectric points (i.e.p.s) in both electrolytes al pH 7.0 for ZrO2 and pH 3.5 for TiO2. A small discrepancy in the i.e.p. toward pH 4 was observed for TiO2 in 10(-3) M NaCl. The i.e.p. of lead oxide in NaCl solution was detected at pH 11.3, whereas in ammonium acetate it could not be defined precisely since dissolution of PbO occurs at pH<6 and precipitation of hydrolytic species occurs at pH>10. Between pH 6 and 10 lead oxide was highly positively charged, giving a relatively stable suspension. According to their i.e.p.s, the oxide components could be classified as slightly acidic (TiO2), neutral (ZrO2) and basic (PbO). Owing to the strong interaction of acetate ion with PbO, a significant shift of the i.e.p. of Pb1.025(Zr,Ti)O3 containing an excess of PbO from pH 6.4 to 4.7 was observed. This could be used as a method for the detection of the free PbO phase in PZT.