Mg-bearing quartz solid solutions as structural intermediates between low and high quartz

Glass powder samples of cordierite composition (doped with 8 mol% TiO2) were heat-treated to produce a series of increasingly SiO2-enriched Mg-bearing quartz solid solutions (Qss). The obtained materials were then analyzed by X-ray diffraction: Rietveld structural refinements revealed that Mg-bearing Qss phases possess trigonal symmetry and a compositionally dependent intermediate structural arrangement between those of low and high quartz. High-temperature diffraction measurements were performed up to 700 degrees C to characterize the thermal expansion behavior of the crystals. At SiO2-rich compositions, a reversible high-to-intermediate inversion of the quartz structure is observed, which shifts with increasing stuffing to lower temperatures than the conventional 573 degrees C for pure quartz. Similarities and differences to the better-established Li-bearing Qss are discussed in the text.

Automated summary

Glass powder samples of cordierite composition, doped with 8 mol% TiO2, were heat-treated to produce a series of Mg-bearing quartz solid solutions enriched in SiO2. Rietveld structural refinements showed that Mg-bearing Qss phases have trigonal symmetry and an intermediate structural arrangement dependent on composition. High-temperature diffraction measurements revealed a reversible inversion of quartz structure at SiO2-rich compositions, occurring at lower temperatures than pure quartz. Similarities and differences to Li-bearing Qss were discussed in the text.