Structural features and thermal expansion of zinc aluminosilicate quartz solid solutions
Alessio Zandonà, Beatriz Paiva Da Fonseca, Gundula Helsch, Vinzent Olszok, Michael J. Pitcher, Haytem Bazzaoui, Alfred P. Weber, Mathieu Allix, Joachim Deubener
Abstract
Zinc aluminosilicate (ZAS) glasses were synthesized along the peraluminous join (SiO2 contents between 95 and 50 mol%) by melt-quenching or sol-gel spray-drying and subjected to controlled heat treatments to obtain ZAS quartz solid solutions (Zn-Qz-ss). The precipitation of Zn-Qz-ss is non-stoichiometric with respect to their parent glass and the crystals undergo a compositional evolution during annealing, even in absence of secondary crystalline phases. Near-hexagonal high-quartz-like crystals with negative thermal expansion (down to -3 × 10-6 K-1) can be obtained in the range 50-80 mol% SiO2, while SiO2-richer crystals exhibit positive thermal expansion at room temperature (up to 29 × 10-6 K-1). Zn2+ ions occupy two distinct positions within the structural channels of quartz, with a strong preference for 4-fold coordination. In analogy to lithium aluminosilicate quartz solid solutions (Li-Qz-ss), the low-to-high phase transition exhibits a linear correlation to the composition of the crystals.