Reactive FAST/SPS sintering of strontium titanate as a tool for grain boundary engineering

A high-pressure FAST/Spark Plasma Sintering method was used to produce dense SrTiO3 ceramics at temperatures of 1050.C, more than 250 degrees C below typical sintering temperatures. Combining SPS with solid-state reactive sintering further improves densification. The process resulted in fine-grained microstructures with grain sizes of similar to 300 nm. STEM-EDS was utilized for analyzing cationic segregation at grain boundaries, revealing no cationic segregation at the GBs after SPS. Electrochemical impedance spectroscopy indicates the presence of a space charge layer. Space charge thicknesses were calculated according to the plate capacitor equation and the MottSchottky model. They fit the expected size range, yet the corresponding space charge potentials are lower than typical values of conventionally processed SrTiO3. The low space charge potential was associated to low cationic GB segregation after SPS and likely results in better grain boundary conductivity. The findings offer a path to tailor grain boundary segregation and conductivity in perovskite ceramics.