March 6-11, 2016
Within the last five years considerable efforts were done in investigating electric field assisted sintering (flash sintering). However the experiments are hard to control: shrinkage occurs within seconds and the local temperature is undefined due to joule heating. Therefore the present study removes these two parameters by investigating grain growth under electric field in the no-current-case for strontium titanate.
The impact of an electric field on grain growth in strontium titanate is investigated between 1350°C and 1550°C for fields of up to 50V/mm. To prevent joule heating by a current flowing through the material insulating Al2O3 plates separate the electrodes from the samples. The seeded polycrystal technique is used, which allows evaluating the grain boundary mobility without an influence of the grain boundary energy. The growth direction of the single crystalline seeds is perpendicular to the electric field; hence electrostatic forces do not influence the growth. Below 1425°C the influence of the electric field is weak. However above 1425°C the field results in an increase of the grain boundary mobility at the negative electrode. The range of this increase is in the order of ~1mm. It is shown that abnormal grain growth can be triggered by the electric field.
Based on the experimental findings a model is established based on a shift of charged defects. The enhancement of the grain boundary mobility on the negative electrode is explained by an accumulation of oxygen vacancies. This accumulation induces a reduction of the material. A reduction of strontium titanate by atmosphere also results in an increase of the grain boundary mobility, which accords well with the observed behavior under electric field.
Wolfgang Rheinheimer, Fabian Lemke, and Michael Hoffman, "Influence of an electric field on grain growth and sintering in strontium titanate" in "Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium", Rishi Raj (University of Colorado at Boulder, USA) Thomas Tsakalakos (Rutgers University, USA) Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/efa_sintering/12