Figure 2c displays a HAADF-STEM mic

Figure 2c displays a HAADF-STEM micrograph focusing on a triple junction, whereas the bottom grain has been tilted to its ⟨001⟩ zone axis. The corresponding scanning transmission electron microscopy−energy-dispersive spectroscopy (STEM-EDS) mapping is shown in Figure 2d with Ti and K elements highlighted. There is an obvious nanoscale K segregation and incorporation into the perovskite grain boundary regions and triple points in Figure 2b. Comparing Figure 2c and Figure 2d, one can note in the EDS data that the K segregation area overlaps with 3−4 atomic layers of BTO unit cells at the bottom grain as viewed here. It indicates that the formation of the grain boundary during cold sintering is accompanied by the incorporation of K-ions into the A-site of the perovskite lattice, with little evidence of the corresponding Na ions being incorporated into these regions. In summary, these observations indicate both high densities, with some preferential incorporation of K+ ions into the lattice near the grain boundaries and at triple points.