The influence of the mixed alkaline earth effect on the structure and properties of (Ca, Mg)–Si–Al–O–N glasses

Abstract

Alkaline earth oxynitride glasses of (Ca, Mg)–Si–Al–O–N with different CaO/(CaO + MgO) molar ratios (0, 0.25, 0.5, 0.75, and 1) were successfully prepared using the sol-gel method, and their structural compositions were characterised by Raman and FT-IR techniques. The glass dynamic properties of thermal expansion coefficient, glass transition temperature (Tg), and static properties of density, molar volume, Vickers hardness and compressive strength were systematically measured and analysed. The results showed that the static properties exhibited an overall regular change as the CaO/(CaO + MgO) ratio gradually increased, while the dynamic properties had an obvious mixed alkaline earth effect, which represented the appearance of an extreme value point in CaO/(CaO + MgO) mole ratios of 0.25 and 0.75, respectively. The typical thermal expansion coefficient and Tg of mixed alkaline earth oxynitride glasses deviated far from the linear connection between single alkaline earth oxynitride glasses. Raman spectra and infrared spectra revealed that the ratio value of the Q3/(Q2+Q4) decreased (Qn: n = no. of bridging anions joining SiO4 tetrahedra) in the mixed alkaline earth oxynitride glasses with increasing the amount of Ca, confirming that Ca decreased the crosslinking between individual tetrahedra via the transformation of Q3 species into Q2 and Q4 species.