Heterogeneous nucleation of Ba1-xSrxZn2Si2O7 from a BaO/SrO/ZnO/SiO2 glass using platinum as nucleation agent

Glasses in the system BaO/SrO/ZnO/SiO2 were doped with 0.01% platinum. During thermal treatment, the glasses were crystallized and the phase Ba1-xSrxZn2Si2O7 was formed. This phase has almost the same structure as the high-temperature phase of BaZn2Si2O7, which shows a negative coefficient of thermal expansion. In the obtained glasses, spherical particles of metallic platinum with diameters in the range from 300 nm to 2 μm are present. Detailed analyses of the curves obtained from differential scanning calorimetry enable the determination of the activation energies as well as the Avrami coefficients. The obtained values of the Avrami coefficients were close to 4, which correspond to three-dimensional bulk crystallization. Scanning electron microscopy was used to identify individual Ba1-xSrxZn2Si2O7 crystals with sizes of approximately 15 μm. Transmission electron microscopy showed that these crystals are nucleated at the surface of spherical platinum particles.