Specific Effect of NiO Dopant on Phase Separation Behavior in Sodium Borosilicate Glass

The effect of the addition of a fourth component on the phase separation behavior in borosilicate glass was focused on to control the development of microstructure during heating. “In‐situ” small‐angle X‐ray scattering spectroscopy (SAXS) was used during heating to observe time scale and transient behavior of phase separation development. The addition of 0.8 mol% NiO in low‐alkali sodium borosilicate (NBS) glass had increased the homogenization temperature by 200 K compared to the dopant‐free glass. Such an effect was not observed with the addition of CoO, CuO, or MgO. By extended X‐ray absorption fine structure (EXAFS) analysis, the nanoclustering of Ni–O–Ni units could be exclusively observed in NiO‐doped NBS glass under phase separation. The critical temperature of phase separation T c was calculated based on the Debye–Hückel theory and successfully predicted this increase of T c , taking into account the formation of high microscopic basicity oxygen in Ni–O–Ni, which was proved by the increase of the Ni–Ni correlation in EXAFS analysis, while other additives do not induce this structural feature.