Fluorine as a Donor Dopant in Barium Titanate Ceramics

We have studied the electrical properties and microstructure of fluorine‐doped BaTiO 3 ceramics. The samples were prepared using a classical ceramic technology that involved the calcination of intimately mixed powders of BaCO 3 , TiO 2 , and BaF 2 . When the samples were sintered in untreated ambient air, the fluorine from the sample reacted with water vapor and formed gaseous HF. To prevent this hydrolysis of the fluorine, we sintered the samples in dried air. The fluorine‐doped BaTiO 3 ceramics sintered in a dry atmosphere showed microstructures and electrical properties typical of donor‐doped BaTiO 3 . The samples containing up to 0.3 mol% of fluorine were coarse‐grained, semiconducting, and displayed a remarkable PTCR effect. In contrast, the samples with a higher fluorine concentration were fine grained and insulating. A SIMS elemental mapping of the samples showed that the fluorine was distributed throughout the microstructure of the semiconducting samples; however, the fluorine concentration was enriched at grain boundaries and in the BaTi 2 O 5 intergranular phase.