SYNTHESIS OF PB(MG1 3NB2/3) O-3 PEROVSKITE BY AN ALKOXIDE METHOD/

Pb(Mg1/3Nb2/3)O-3 materials have been synthesized using sol-gel, freez e-drying or spray-pyrolysis techniques. The as-prepared powders were o f an amorphous form which could be converted into a crystalline form b y calcination. The pyrochlore phase was inevitably formed with an acco mpanying perovskite phase. As the calcining temperature increased, gre ater proportions of the desired perovskite phase occurred. The residua l pyrochlore phase could be completely transformed into the perovskite phase when the powders were prepared via freeze-drying or by a spray- pyrolysis method. The maximum proportion of the pyrochlore phase was, however, only 92% when the powders were synthesized by a sol-gel route . Thermal gravimetric analysis/differential thermal analysis (TGA/DTA) and infrared transmission spectroscopy (FTIR) indicated that Mg(OEt)( 2) and Nb(OEt)(5) formed a double alkoxide but Pb(OAc)(2) formed separ ate clusters during the hydrolysis of the solution in the sol-gel proc ess. Inhomogeneous mixing meant that the intermediate phase formed was rather difficult to eliminate completely. Homogeneous mixing was pres erved when the solution was directly freeze dried or spray pyrolysed. The size of the preferentially formed pyrochlore phase was very fine a nd further transformation was feasible. Pb(Mg1/3Nb2/3)O-3 materials, f ree of the pyrochlore phase, could therefore be obtained.