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 lea st two phase: tetragonal and rhombohedral. Free PbO was found in the l ead-zirconate-titanate (PZT) sample when an excess of lead oxide was a dded to the reaction mixture. In order to determine the isoelectric co nditions 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 sm all 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 hydrolyt ic species occurs at pH>10. Between pH 6 and 10 lead oxide was highly positively charged, giving a relatively stable suspension. According t o their i.e.p.s, the oxide components could be classified as slightly acidic (TiO2), neutral (ZrO2) and basic (PbO). Owing to the strong int eraction 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 o bserved. This could be used as a method for the detection of the free PbO phase in PZT.