THE INFLUENCE OF DOPING ON FLASH SINTERING CONDITION IN SrTi_1-xFe_xO_3-δ

The innovative flash sintering process raised a great interest in the past few years due to its applicability in various engineering fields and the interesting scientific questions it evokes. This technique could be beneficial in many applications since it reduces the time and cost of the sintering process. Joule heating can explain the sudden temperature rise of the sample, which enhances the rate of grain boundary diffusion. However, for a given material the sample`s temperature remains lower than the temperature at conventional sintering. Although Joule heating is a significant phenomenon, it is proposed that lattice defects and their transport properties are also influenced by the applied field and can play an important role in the flash sintering process.

Here, five different SrTi_1-xFe_xO_3-δ samples (x=0, 0.1, 0.5, 1, 3), were chosen as a model material to examine the influence of dopants on the threshold conditions of flash sintering (i.e., temperature and applied electric field). The threshold conditions indicate that the temperature decreases when doping is increased. This result can be explained both by the increase of the electric conductivity that affects directly the Joule heating; and by the existence of added ionic defects in the lattice.

In a doped semiconductor, extrinsic defects can be compensated electronically and by self-compensation. The analysis of point defect concentration was done using the doping factor concept. The doping factor, f, is defined by the ratio between the electron concentration after introducing a dopant and the electron concentration at a reference state. Substituting the new electron concentration in the mass action relations of all the defects yields new values for their concentrations in the doped material, expressed by the same factor f.