In the case of BaTiO3 and SrTiO3, which have poor solubility in water, a molten hydroxide flux (a mixture of NaOH and KOH) could also assist the cold sintering of the systems [35].And reactive intermediate solutions could be added, a solution containing water-soluble Ba(OH)2 and nano-grade TiO2 powders has been used in the CSP of BaTiO3. The mixed solution that was transformed to a solid phase after the CSP was located between the BaTiO3 particles. Densification was achieved after post-annealing at 950 °C, in which the heat- treatment played an important role in improving the density [24, 25].