Pyrochlore-free Pb(Mg1/3Nb2/3)O3 prepared by a combination of the partial oxalate and the polymerized complex methods

Pyrochlore-free Pb(Mg1/3Nb2/3)O-3 (PMN) powders were successfully synthesized by the partial oxalate (PO) method using a high reactive MgNb2O6 (MN) precursor powder synthesized by the polymerized complex (PC) method. Raman spectroscopy, X-ray diffraction and nitrogen gas adsorption/desorption isotherms were used to characterize the MN precursor. No evidence of impurities in the MN precursor was found. Lead oxalate synthesized in situ was precipitated onto the surface of MN nanoparticles. The material was filtered, washed and calcined at different temperatures, from 700 to 1000 degreesC, in air for 2 h to obtain the PMN phase. Thermal analysis, X-ray diffraction and nitrogen adsorption/desorption hysteresis were used to investigate the PMN perovskite phase evolution and the presence of the pyrochlore phase. PMN formation is a function of the time and temperature conditions of the precipitate calcination, and an optimum condition for the thermal decomposition of the precipitate was determined to avoid the formation of the pyrochlore phase. (C) 2001 Elsevier Science B.V. All rights reserved.