Intermediate Phase Development in Phosphorus‐Doped Barium Titanate

In the present work, the phase formation and thermal evolution in phosphorus‐doped BaTiO 3 have been studied using differential thermal analysis, X‐ray diffractometry, scanning electron microscopy coupled with energy‐dispersive spectroscopy, transmission electron microscopy, and high‐temperature nuclear magnetic resonance. Phosphorus cations that are incorporated from ester phosphate form a surface layer that covers the BaTiO 3 particles. This layer acts as a reactive coating during sintering. Phosphorus‐doped BaTiO 3 samples that have been treated at temperatures of 650°–900°C show the presence of crystalline Ba 2 TiP 2 O 9 and/or Ba 3 (PO 4 ) 2 phases. The appearance of secondary phases is dependent on the cooling rate. Higher temperatures (900°–1200°C) result in the presence of a phosphorus–BaO‐rich phase that covers the BaTiO 3 particles. As a consequence, the remaining titanium‐rich BaTiO 3 drives the formation of a liquid phase at temperatures >1200°C. In regard to the reported sintering behavior of P 5+ ‐doped BaTiO 3 , the formation of a phosphorus–BaO‐rich phase that covers the BaTiO 3 particles could be the origin of the improved porosity coalescence and removal that is observed at the earlier stages of sintering.