Intermediate phase development in phosphorus-doped barium titanate

In the present work, the phase formation and thermal evolution in phosphoru s-doped BaTiO3, have been studied using differential thermal analysis, X-ra y diffractometry, scanning electron microscopy coupled with energy-dispersi ve spectroscopy, transmission electron microscopy, and high-temperature nuc lear magnetic resonance. Phosphorus cations that are incorporated from este r phosphate form a surface layer that covers the BaTiO3, particles. This la yer acts as a reactive coating during sintering. Phosphorus-doped BaTiO3, s amples that have been treated at temperatures of 650 degrees-900 degrees C show the presence of crystalline Ba2TiP2O9 and/or Ba-3(PO4)(2) phases. The appearance of secondary phases is dependent on the cooling rate. Higher tem peratures (900 degrees-1200 degrees C) result in the presence of a phosphor us-BaO-rich phase that covers the BaTiO3, particles. As a consequence, the remaining titanium-rich BaTiO3, drives the formation of a liquid phase at t emperatures >1200 degrees C. In regard to the reported sintering behavior o f P5+-doped BaTiO3, the formation of a phosphorus-BaO-rich phase that cover s the BaTiO3, particles could be the origin of the improved porosity coales cence and removal that is observed at the earlier stages of sintering.