Mechanical niobium doping in barium titanate electroceramics

Niobium is a well-established donor dopant for semi-conducting BaTiO ₃ ceramics. The conventional procedure to dissolve Nb into BaTiO ₃ relies on thermal activation at high temperatures (up to 1500 °C) and even then, large dwell times are necessary due to the small diffusion coefficients of Nb5 +. In this work, we demonstrate a new doping procedure by Mechanical Alloying (MA), which has already proven its potential for the fabrication of conductive electroceramics. In a planetary mill, powders of BaTiO3 and Nb2O5 were mixed for up to 540 min. The BaTiO3 unit cell volume increases with increasing Nb concentration. The electrical properties of conventional and mechanical alloyed samples as a function of Nb concentration are similar, however the mechanically alloyed samples shows a large conductivity that we attribute to a better homogeneity in the structure of MA-processed samples. For small dopant concentrations, charge compensation of the pentavalent Nb is primarily attributed to free electrons. At higher Nb concentrations cation vacancies prevail as compensation mechanism.