In this study, we choose BaTiO3 with Sr(OH)2·8H2O as a model system to investigate themechanism due to the following reasons. Building from the work that we have developed on CSP of BaTiO3 using Ba(OH)2·8H2O as a sintering flux,22 we now consider the chemistry of Sr(OH)2·8H2O as a similar flux for the densification of BaTiO3. In addition, Sr2+ is a well-known ion that can be easily incorporated into BaTiO3, demonstrated by both conventional sintering23 and hydrothermal reaction.24 Even in CSP, Sr is expected to be incorporated into the lattice host of BaTiO3 through the dissolution-precipitation process and also act as a tracer atom to investigate precipitation pathways. In previous studies, isotopes such as deuterated water in potassium dihydrogen phosphates (KDP), was used to trace a shell formation consistent with the direct evidence of precipitation and imaging the microstructure via time-of-flight secondary ion mass spectrometry (TOF-SIMS).25 In our case, we can more easily detect Sr using simple measurements, such as energy-dispersive X-ray spectroscopy (EDS), without overlaps in energy peak, and obtain nanoscale levels of spatial resolution. With these advantages, we consider the fabrication of BaTiO3- Ba1-xSrxTiO3 via CSP with a flux of Sr(OH)2·8H2O. In addition, using transmission electron microscopy (TEM)-EDS analysis, we discuss CSP mechanisms at a nanoscale, enabling the fabrication of high dense ceramics at extremely low temperatures.