Thermal expansion and glass transition temperature of the rare-earth doped oxynitride glasses

Thermal expansion coefficients (α), glass-transition (Tg) and Littleton (TL) temperatures, hardness and density of the RE–Si–Mg–O–N glasses (RE=Sc, Y, La, Nd, Sm, Gd, Yb, and Lu) were investigated to separate the effects of rare-earth elements and nitrogen on the properties of bulk glasses. These properties depend approximately linearly on nitrogen content, density of the glass and ionic radius of the corresponding lanthanide. Lanthanides modify hardness of the studied oxynitride glasses with 20–24 eq.% N by 11.4–14.4%, α by ∼13%, Tg by 31–35 °C, and TL by 33–43 °C. Deviations from linearity found in Nd-, Sm- and Yb-doped glasses were possibly due to valence change. Non-lanthanide dopants, Sc and Y, often do not fit the dependence but result in comparable properties. The effects of nitrogen and rare-earth dopants are independent and additive.