X-ray studies of phase transitions of (Ca,Sr)-(a)over-circle-kermanite solid solutions

The phase transitions of the solid solutions (Ca1-xSrx)(2)MgSi2O7 (0 less t han or equal to x less than or equal to 0.32) of modulated melilites are st udied by X-ray diffraction. The variation of the intensity and the FWHM of satellite reflections reveal different transition temperatures. Two ranges of different ordering are found in the range of incommensurate modulation. The mechanism of the phase transition into the incommensurately modulated s tructure is discussed by including the diffuse scattering above the transit ion.