Electric Field-Assisted Pressureless Sintering of Ceramic Protonic Conductors

Gadolinium, yttrium and samarium-doped barium cerate pressed pellets were submitted to flash sintering experiments isothermally in the temperature range 800-1300^oC under 200 V cm^-1 electric field. The pellets were positioned inside a dilatometer furnace with Pt-Ir electrodes connected either to a power supply or to an impedance analyzer to evaluate the bulk and the grain boundary contributions to the electrical resistivity. Near full density was achieved in the sintered samples. The combined results of dilatometry and impedance measurements in conventionally and flash sintered specimens show substantial improvement of the electrical conductivity. Joule heating is assumed to be the primary effect for sintering. Improved grain-to-grain contact and the removal of depleted chemical species due to Joule heating at the space charge region are proposed, respectively, as the reasons for the decrease of the grain boundary component in the impedance diagrams and the improvement of the bulk electrical conductivity.