Crystal structure of Sr-akermanite glass–ceramics

A glass–ceramic of Sr-akermanite (Sr2MgSi2O7, SG: P 4 ¯ 2 1 m ) was prepared by crystallization of a glass with composition of 2SrOMgO3SiO2. Parameters of the crystal structure were refined by Rietveld method. The analysis of the experimental results showed the following: the unit cell of Sr-akermanite in the glass–ceramic is larger than in single crystal. The thermal expansion coefficients of Sr-akermanite, calculated from the lattice constants obtained from X-ray diffractograms at high temperatures, were αa = 3.663 × 10−6 K−1 and αc = 6.666 × 10−6 K−1. It is suggested that the atomic displacements from the atomic coordination in single crystal depend on the stress developed during the crystallization process and the thermal contraction stress developed during cooling. Both types of stresses are related to the presence of residual glass and should be responsible for the expansion of the crystal lattice.