Niobium pentoxide (T form, orthorhombic system) was utilized to promote devitrification in Li 2 O · Al 2 O 3 · 6SiO 2 glasses. Two or more mole percentage of this nucleating dopant enhanced crystallization in these glasses. Glasses containing 4.0 and 8.0 mol% T‐Nb 2 O 5 exhibited a high tendency to form dispersed TT‐Nb 2 O 5 (monoclinic system) precipitates during the glass quenching process. The crystallization process in glasses containing 2.0 or 4.0 mol% T‐Nb 2 O 5 occurred as microphase separation, followed by the formation of dispersed TT‐Nb 2 O 5 crystalline precipitates (760°C), followed by β‐quartz solid‐solution ( ss ) formation (850° to 900°C) heterogeneously nucleated from the precipitates. β‐quartz( ss ) transformed to β‐spodumene( ss ), along with a polymorphic transition from the TT‐Nb 2 O 5 to M‐Nb 2 O 5 (tetragonal system) crystalline phase.
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Hsu et al. (1991) studied this question.
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