Raman and infrared investigations of glass and glass-ceramics with composition 2Na₂O · 1CaO · 3SiO₂

Precursor glass and glass-ceramics with molar composition 2Na₂O · ICaO · 3SiO₂ are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm⁻¹, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm⁻¹, attributed to symmetric stretching vibrations of SiO₄ tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm⁻¹, associated with vibrations of SiO₄ tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.