This article investigates the structural heterogeneity in a silicate glass by hyperquenching-annealing-calorimetry approach. The results show a striking phenomenon - two separated subTg relaxation peaks appear on the calorimetric curve of the hyper-quenched CaO-MgO-SiO2 glass, implying the existence of two distinct structural domains of higher and lower potential energies respectively. The higher energy domains in nanoscale are so unstable that they become ordered during hyperquenching. This is verified byt he high-resolution transmission electron microscopy image exhibiting nano-ordered domains in the glass matrix. The higher energy domains relax similar to a strong glass phase, whereas the lower energy domains do similar to a fragile one.
