Thermal decomposition and kinetic analysis of relaxor ferroelectric lead magnesium niobate

The reaction mechanisms and kinetics of thermal decomposition of the relaxer ferroelectric Pb(Mg1/3Nb2/3)O-3 powder at elevated-temperatures have been investigated. The decomposition of Pb(Mg1/3Nb2/3)O-3 is characterized by an initial formation of pyrochlore phase, associated with evaporation of PbO. Then pyrochlore phase subsequently gets dissociated, resulting lit the formation of Mg4Nb2O9 and MgNb2O6. The decomposition amounts of Pb(Mg1/3Nb2/3)O-3 as well as pyrochlore phase increase monotonously with increase in the reaction temperature and rime. Based on the isothermal analysis of reaction kinetics, the rate-controlling step for decomposition of Pb (Mg1/3Nb2/3) O-3 is determined to be the chemical reaction of Pb(Mg1/3Nb2/3)O-3 itself with activation energy of 234 kJ mol(-1). On the other hand, during the decomposition of pyrochlore phase, a molten microstructure is formed, and reaction kinetics changes greatly. This decomposition of pyrochlore phase is confirmed to be a first-order reaction with higher activation energy of 407 kJ mol(-1). (C) 1998 Elsevier Science Limited. All rights reserved.