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Transparent glass-ceramics based on ZnO–Al 2 O 3 –SiO 2 (ZAS) glass system exhibit excellent optical and mechanical properties that are dependent on crystal grains. Gahnite (ZnAl 2 O 4) was the main phase that crystallized in ZAS glass-ceramics via thermoelectric coupling treatment. The morphology and size of ZnAl 2 O 4 crystal were controlled by the electric field strength. Introduction of thermoelectric coupling field led to the refinement and dispersion of large and agglomerated ZnAl 2 O 4 crystal grains, which improved the transmission and Vickers' hardness of the ZAS-based glass-ceramics. Theoretical calculations revealed that crystal phase is the area of low electric field strength, which resulted in the migration of Zn ions (Zn2+) from glass phase to the ZnAl 2 O 4 crystal regions under the effect of thermoelectric coupling field. The decrease in the amount of Zn2+ in glass phase further limited its grain growth, and refinement of ZnAl 2 O 4 grains was achieved. This research shows an efficient and rapid approach to refine grains in ZAS glass-ceramics by application of thermoelectric coupling treatment. • In this work, it is the first time use of thermoelectric coupling field to precipitate ZnAl 2 O 4 nanocrystals in ZnO–Al 2 O 3 –SiO 2 glass-ceramics. • The application of a thermoelectric coupling field was used to refine and uniformly distribute ZnAl 2 O 4 crystals in ZnO–Al 2 O 3 –SiO 2 glass-ceramics. • The mechanism of a thermoelectric coupling field on crystal refinement is explained in detail, which provides ideas for the refinement and uniformly distribution of crystal grains. [ABSTRACT FROM AUTHOR]

The Li 2 O–Al 2 O 3 –SiO 2 (LAS) glass ceramics are prepared by one-step thermoelectric treatment. The influence of thermoelectric treatments on LAS glass-ceramics were studied. The crystal phase composition and microstructure of the LAS glass-ceramics were investigated by DSC, SEM, XRD and FTIR. Moreover, the thermal expansion performance and light transmittance of LAS nanocrystalline glass were characterized. The results show that low-expansion transparent LAS nanocrystalline glass can be produced in a short time by thermoelectric treatment. The free energy of nucleation and the degree of polymerization of the glass network are reduced by the electric field. The key is that the electric field polarizes Ti and Zr ions at the crystallization temperature, so that the crystal nuclei repel the same poles. This allows uniform crystal distribution, promotes crystallization and reduces one-step crystallization of crystal agglomeration. This proves that the rapid preparation of nanocrystalline glass by the one-step method is feasible, and provides a reference for the future one-step processing of glass-ceramics. • Thermoelectric treatment promotes crystallization in LAS nanocrystalline glass. • It eliminates crystal agglomeration in LAS nanocrystalline glass. • It can rapidly produce low-expansion transparent LAS nanocrystalline glass. [ABSTRACT FROM AUTHOR]

• First report to control the precipitation of crystal grains under thermoelectric coupling. • The number of crystal grains gradually increases with the electric field voltage. • Fracture of the Ti-O-Si bond causing [TiO 4 ] will be transformed to [TiO 6 ]. MgO–Al 2 O 3 –SiO 2 (MAS) the basic glass was prepared by the traditional melt-quenching method, whereas the glass-ceramics was produced by subjecting the glass to thermoelectric coupling treatment. The MAS glass-ceramics were characterized by FTIR, XPS, and SEM. Clearly, the extension of the heat-treatment time did not change the crystal grains number in the absence of an electric field. However, with the electric-field voltage increase,the crystal grains number in the MAS glass-ceramics gradually increased when the electric-field voltage became steady at 1200 V. At high temperatures, Ti4+ participates in the silicon-oxygen network with four coordinations and produces good miscibility with the melt. By the introduction of electric field into the glass, a high amount of titanium transforms from a titanium-oxide tetrahedron to a titanium-oxide octahedron. Titanium was separated from the silicon–oxygen network framework to form a crystal nucleus and promote crystal growth. This study provides insights into the relationship between electric-field and glass-ceramics nucleation. [ABSTRACT FROM AUTHOR]