Perovskite phase formation and microstructural evolution of lead magnesium tungstate-lead titanate ceramics
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The perovskite phase formation and microstructural evolution in the Pb(Mg0.5W0.5)O3-PbTiO3 system have been investigated in this work. During the solid-state reaction of Pb(Mg0.5W0.5)O3, only PbWO4 and Pb2WO5 are formed as intermediate phases at low temperature range. Moreover, the perovskite phase Pb(Mg0.5W0.5O3 begins to form at 600 °C and is complete at 850 °C. As Pb(Mg0.5W0.5)O3 is doped with PbTiO3, the formation of the perovskite phase becomes sluggish and the temperature for the complete reaction to take place increases up to 1000 °C. The doping of the Pb(Mg0.5W0.5)O3 with PbTiO3 apparently induces the formation of a small amount of liquid phase, which is possibly attributed to a reaction with residual Pb2WO5. This liquid phase not only accelerates the densification of specimens through a liquid phase sintering mechanism, but also causes abnormal grain growth, thereby forming an inhomogeneous microstructure. The dielectric permittivity of Pb(Mg0.5W0.5)O3 does not depend on frequency, and a sharp phase transformation from the antiferroelectric to the paraelectric state occurs at around 40 °C. In contrast, the dielectric properties and broad phase transformation temperatures of Pb(Mg0.5W0.5)0.9Ti0.1O3 and Pb(Mg0.5W0.5)0.6Ti0.4O3 strongly depend on frequency. This dependency would imply that the PbTiO3 addition to Pb(Mg0.5W0.5)O3 alters the order arrangement of B-site cations to a disordered state and induces relaxor-ferroelectric characteristics.
KeywordsPhase Transformation Microstructural Evolution Dielectric Permittivity Transformation Temperature Perovskite Phase
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