Formation of a High-Temperature Liquid Phase During the Sintering of PbFe2/3W1/3O3

A high-temperature liquid phase (rather than a low-temperature liquid phase at 690°C as reported recently) has been demonstrated to form at 860°C on heating and to solidify at 840°C on cooling in PbFe_2/3O₃. This liquid phase not only promotes densification, but also induces the formation of rounded PbFe_2/3W_1/3O₃ grains during sintering at 870°C. Through slow cooling at a rate of 25°C/h after sintering, platelike grains, designated G phase, are found to form in a thin surface layer of specimens. This formation of platelike G phase is considered to be related to the solidification and recrystallization of the liquid phase exuded from the interior. The amount of the G phase on the surfaces decreases with the increase of cooling rates, indicating that fast cooling will lead the liquid phase to be solidified in the bulk of specimens. These results reveal that the microstructure of PbFe_2/3W_1/3O₃ is greatly affected by the high-temperature liquid phase; additionally, the slow cooling treatment seems to be a direct and effective method for removing the residual liquid phase from PbFe_2/3W_1/3O₃.