Crystallization, structure and thermal expansion properties of quartz solid solutions crystallized in copper aluminosilicate sol-gel glasses

In order to expand the range of available quartz solid solutions (Qz-ss), copper aluminosilicate glasses were produced through different sol-gel methods. Favorable sample compositions were selected by analyzing dip-coated thin layers with different SiO 2 contents and CuO/Al 2 O 3 ratios. The phase assembly proved to be complex, as many different phases crystallized simultaneously, hampering stoichiometric precipitation of Qz-ss from the starting glasses. Despite these challenges, systematic heat treatments of four different spray-dried compositions with Al/Si ratios from 0.05 to 0.5 enabled the formation of Cu-stuffed Qz-ss with different structural stuffing degrees. The thermal expansion coefficients of the low and high temperature modifications of the different Qz-ss varied from 0.4 to 26 × 10 –6 K -1 , with no negative thermal expansion being detected. Copper ions are accommodated in both tetrahedral and octahedral sites in the Qz-ss channels, and the blue-green hue seen in the spray-dried powders may be assigned to Cu 2+ in 6-fold coordination.