Transitional Phase of Ca 2 SiO 4 Solid Solution with Incommensurate Superstructure

Crystals of Ca 2 SiO 4 doped with K, P, Al, and Fe were grown and examined by means of both X‐ray and electronbeam diffraction. They are made up of domains 120° different in orientation around the c axis of the previous α phase. Each of the domains gives an orthorhombic superstructure whose cell is incommensurate with the underlying orthorhombic subcell with a=0.540, b=0.936, and c=0.681 nm. This orthorhombic phase, characterized by the cell edge length of 3.8a, is termed 3.8aC 2 S(ss). Both the domain and the incommensurate structure strongly suggest that this is the precursor to a phase thermodynamically more advantageous at lower temperatures.