Tetragonal-orthorhombic phase transformation and sintering behavior of KSbOSiO₄ (isomorphous derivative of KTP)

Fine KSbOSiO₄ (KSS) powders have been prepared by a sol-gel method starting from the system of TEOS, KSb(OH)₆, H₂O, C₂H₅OH, or mechanochemical mixing method with a stoichiometric mixture of amorphous silica and KSb(OH)₆. The KSS crystallized sluggishly into a tetragonal symmetry in low temperature and transformed into an orthorhombic one in higher temperature, indicating the amorphous-like powder patterns in the intermediate step. This amorphization process could be related to some redistribution of the polysilicate network structures. The mechanochemical activation energy stored in the powder surface, as well as the coexisting matrix (KSbO₃), retards the transformation. It was concluded that the KSS powders composed of high molecular weight siloxane polymers, which were formed by hydrolysis in the presence of a small amount of NH₃ aqueous solution, showed higher sinterability. The sintering, where the calcining process was omitted, enabled the dense tetragonal-type ceramics stabilized at lower temperature, rather than higher temperature, to fabricate.