Structural change in phosphorus-bearing dicalcium silicates

Structures of (Ca2-x/2 square x/2) (Si1-xPx)O-4 crystals were examined as a function of x ranging from 0.03 to 0.40. All of the samples were heated at the stable temperature region of the alpha-phase and then quenched in water, The phase constitution at ambient temperature was classified into three categories according to the fraction of the alpha-to-alpha'(H) transition, When the transition was completed as in the crystals with x less than or equal to 0.100, the beta- and alpha'(L)-phases were obtained, the relative amounts of which were determined by the start and finish temperatures of the alpha'(L)-to-beta martensitic transformation, With 0.125 less than or equal to x less than or equal to 0.150, the alpha-to-alpha'(H) transition was incomplete, During further cooling, the product alpha'(H)-phase was inverted to the alpha'(L)-phase, and the residual alpha-phase was inverted to the incommensurate phase successively. Because the start temperature of the alpha'(L)-to-beta transformation was lower than ambient temperature, the alpha'(L)-phase was stabilized. With x greater than or equal to 0.175, all of the crystals were free from the alpha-to-alpha'(H) transition. The crystals with 0.175 less than or equal to x less than or equal to 0.225 were made up exclusively of the incommensurate phase. A good correlation existed between the modulation wavelength (=N) and the P/(Si+P) ratio (=x) as N=4.134-1.56x (0.175 less than or equal to x less than or equal to 0.250). With 0.275 less than or equal to x less than or equal to 0.300, the crystals were isostructural with alpha-Ca2SiO4. The hexagonal phase with 0.350 less than or equal to x less than or equal to 0.400, probably a transition product from the oc-phase,showed two-dimensional modulations along the a-axis with N=2 and along the c-axis with N=3.