Reduction of Ti 4+ to Ti 3+ in Boron‐Doped BaTiO 3 at Very Low Temperature

Reduction of Ti 4+ to Ti 3+ was found in boron‐doped BaTiO 3 ceramics when we sintered the samples at very low temperature (>850°C) in 5%H 2 /Ar. Such reduction did not occur in pristine BaTiO 3 ceramic. The methods such as UV –vis spectroscopy, luminescence spectroscopy, and X ‐ray photoelectron spectroscopy confirmed the reduction by showing the presence of Ti 3+ . The results of Ti–K‐edge X ‐ray absorption near‐edge structure measurement ( XANES ) indicated that boron doping changed the geometry of Ti‐oxygen in BaTiO 3 to some extent. It was likely that some boron ions stayed at interstitial sites of BaTiO 3 lattice and acted as donors, which might trigger the reduction. The reduced boron‐doped BaTiO 3 were semiconducting and had very low room‐temperature resistivity (<100 Ω m). However, different from the n ‐type rare‐earth‐doped BaTiO 3 ceramics, they did not display positive temperature coefficient resistance ( PTCR ) behavior.