AN X-RAY AND GRAVIMETRIC STUDY OF THERMAL SYNTHESIS OF PZT SOLID SOLUTION FROM OXALATE PRECURSOR

Abstract

The results of thermogravimetric and XRD studies of thermal decomposition of oxalate precursor of morphotropic PZT solid solution Рb(Zr0.52Ti0.48)O3 are presented. Oxalate precursor Pb[(Ti0,48Zr0,52)(C2O4)3]∙4H2O was obtained by precipitation reaction using titanium tetrachloride TiCl4, zirconium oxychloride ZrOCl2∙8H2O, lead nitrate Pb(NO3)2, oxalic acid H2C2O4∙2H2O and ammonia NH3 25% water solution as starting materials. According to thermogravimetric data, the loss of water molecules from the oxalate precursor takes place before 200°C, the decomposition rate increases sharply after the loss of first of three oxalate groups at about 250°C and the loss of all oxalate groups is practically complete at 350°C. XRD diffraction patterns of heat treated precursor samples confirm complete decomposition of oxalate groups before 350°C, then crystallization of PbO is observed and PbTiO3 and PbZrO3 appear at 450°C. Further increase in temperature of one-stage heat treatment leads to an increase in amounts of PbTiO3 and PbZrO3 but homogeneous PZT solid solution is not observed even at 800°C. There is antagonism between the rate of solid-state reactions between simple oxides formed in precursor decomposition and, from the other hand, the rate of particle growth for these oxides. To overcome this difficulty, a two-stage schedule of heat treatment was proposed: dwelling the precursor at 380°C and quick heating and dwelling at 800°C. Using this regime a homogeneous PZT solid solution has been synthesized.