Crystallization sequence within the keatite solid solution – cordierite mixed compositional triangle with TiO2 as nucleating agent

Inversion of quartz solid solutions at cryogenic temperatures

“…All analyzed glass powders could be crystallized into Qss, although they also inevitably developed non‐negligible amounts of Kss (Figure 2A). The early occurrence of this phase was not unexpected due to its thermodynamic stability at these compositions 8 and was in accordance with previous results in TiO 2 ‐nucleated glass‐ceramics 22 . Moreover, the formation of Kss did not appear to induce undesired compositional shifts of the Qss phases, whose lattice parameters at room temperature matched the values expected from literature sources (Figure 3).…”

“…These previous works invariably obtained Qss by devitrification with the exception of Henglein 9 and Carpenter et al, 30 who examined naturally occurring crystals, and Xu et al, 14 who also employed high‐temperature sintering and high‐temperature high‐pressure protocols 31 . Concerning additional data points from glass‐ceramics containing nucleating agents (typically TiO 2 and ZrO 2 10,22,32 ), they are more scattered, but show a general agreement with the trend of stoichiometric references (square points in the figure). Notice that all points are plotted according to the nominal composition of the obtainable Qss crystals in the samples (Table 1), as most of the other authors did before us.…”

“…A, a lattice constant, (B) c lattice constant, and (C) unit cell volume of Qss as obtained at room temperature for all analyzed LAS crystals, plotted against their nominal SiO 2 content and in comparison with various literature sources 9‐11,14,22,30,32 (* labels the lattice parameters of pure high quartz extrapolated to room temperature). The data from Ray and Muchow (1968), Carpenter et al (1998), Xu et al (2001) and this work were used for linear interpolation.…”

“…Unit cell volumes of Kss obtained in the samples analyzed within this work, plotted as a function of the nominal SiO 2 content of the crystals and in comparison with available literature references 22,34 ; error bars are smaller than the depicted symbols [Color figure can be viewed at wileyonlinelibrary.com]…”

“…This observation, though in accordance with previous theoretical predictions, 19 was based on a single T c data point for temperatures below ambient, 17 due to the special instrumentation required at these challenging conditions. Note that Qss phases can be also obtained if Mg and Zn are employed as stuffing cations instead of Li 10,11,20‐23 . Particularly in the case of Mg doping, however, the univocal assignment of their structure to a high or low quartz symmetry is still debated 24‐26 …”