Darko Makovec, Nina Ule
Jožef Stefan Institute, Jamova 39,1000 Ljubljana, Slovenia
Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, Maribor, Slovenia, also part-time at Jožef Stefan Institute
BaTiO3 ceramics were exposed to fluorine-containing atmosphere prepared by introducing a fluorination agent (CF3CH2OH) into a hot alumina-tube furnace. The fluorinated samples were studied using SEM and TEM. The fluorination resulted in the formation of a surface-reaction layer with a complex structure. At the reaction front fluorine reacts with BaTiO3 to produce BaF2 and BaTi2O5. During the course of the fluorination the BaTi2O5 reacts further to produce BaF2 and then subsequently Ba-polytitanates with an increasing content of titanium, and finally TiO2. Fluorine also diffuses along the grain boundaries towards the pellet’s interior. The presence of the fluorine stabilises the BaTi2O5 compound and consequently triggers its formation in the ceramic’s interior in a reaction between BaTiO3 and the intergranular phase Ba6Ti17O40.