Mechanical niobium doping in barium titanate electroceramics

摘要

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 Nb~(5+). 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 BaTiO_3 and Nb_2O_5 were mixed for up to 540 min. The BaTiO_3 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.