Control samples were created to dec

Control samples were created to decouple the various steps of the method. Table 1 gives the densities achieved for ceramics fabricated under various conditions. Ceramics were uniaxially pressed without heating or addition of solution, followed by heating at 950
C. In these cases, neither ceramic (solid state or nanopowder) showed any sign of sintering, and were mechanically unstable. Further ceramics were created with added intermediate phase solution but without the in-press heating step (i.e. solution was mixed into the SrTiO3, pressed at room temperature and heated at 950
C). The densities of these control ceramics were found to be 63.2  1.7% for the solidstate powder and 63.1  2.9% for the nanopowder calculated using the dimensions and mass (measurements using the Archimedes method were found to be unreliable due to the high level of open porosity of the ceramics). Although mechanically stable, the low density of these ceramics indicates the importance of the heated pressing step. The heated-pressing step (at the heart of the cold sintering process) enables rearrangement and compaction of the particles due to a mobile hydrated phase, followed by recrystallisation of the added strontium chloride phase (Fig. 1c). This allows the multiphase ceramic to retain the densied state until the post-press heating step. Without the concurrent heating/pressing step this densication is lost upon removal of the applied load, as the green body relaxes. Hence, we conclude that the heated pressing step is vital for the production of dense ceramics by “freezing in” the particle compaction through recrystallisation of the SrCl2 phase.