Acta Crystallographica Section B

Structural Science, Crystal Engineering and Materials

Volume 69, Part 2 (April 2013)

research papers

Acta Cryst. (2013). B69, 110-121    [ doi:10.1107/S2052519213001401 ]

Crystal structure and microstructure of synthetic hexagonal magnesium-cobalt cordierite solid solutions (Mg2-2xCo2xAl4Si5O18)

F. J. Serrano, N. Montoya, J. L. Pizarro, M. M. Reventós, M. A. Kojdecki, J. M. Amigó and J. Alarcón

Abstract: Co2+-containing cordierite glasses, of nominal compositions (Mg1-xCox)2Al4Si5O18 (with x = 0, 0.2, 0.4, 0.6, 0.8 and 1), were prepared by melting colloidal gel precursors. After isothermal heating at 1273 K for around 28 h, a single-phase [alpha]-cordierite (high-temperature hexagonal polymorph) was synthesized. All materials were investigated using X-ray powder diffraction and field-emission scanning electron microscopy. The crystal structure and microstructure were determined from X-ray diffraction patterns. Rietveld refinement confirmed the formation of magnesium-cobalt cordierite solid solutions. The unit-cell volume increased with the increase of cobalt content in the starting glass. The crystalline microstructure of the cordierites was interpreted using a mathematical model of a polycrystalline material and characterized by prevalent crystallite shape, volume-weighted crystallite size distribution and second-order crystalline lattice-strain distribution. Hexagonal prismatic was the prevalent shape of [alpha]-cordierite crystallites. Bimodality in the size distribution was observed and interpreted as a consequence of two paths of the crystallization: the nucleation from glass of [mu]-cordierite, which transformed into [alpha]-cordierite with annealing, or the nucleation of [alpha]-cordierite directly from glass at high temperatures. Scanning electron microscopy images agreed well with crystalline microstructure characteristics determined from the X-ray diffraction line-profile analysis.

Keywords: cordierite; crystalline microstructure; volume-weighted crystallite size distribution; second-order crystalline lattice-strain distribution; crystallite shape; glass; Rietveld analysis; X-ray diffraction line-profile analysis; powder X-ray diffraction pattern modelling.

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