Abstract
The introduction of rare earth elements in protecting coatings against degradation due to chemical interactions with liquid silicates as CMAS (CaO–MgO–Al2O3–SiO2) is very promising. They lead to the precipitation of several silicates, as cyclosilicate and apatite phases. In this work, rare earth cyclosilicate phases with formula Ca3RE2(Si3O9)2 (RE = Nd, Sm, Gd, Dy, Yb) and space group C2/c have been prepared by solid state reaction at 1400 °C. High purity powders (with few percents of apatite as impurity) have been obtained. XRD characterization has been performed via synchrotron and the patterns were refined by Rietveld method. Considering that the ionic radius of Ca2+ is larger than the ionic radius of all the RE3+ studied here, the repartition of both cations in the three cationic sites of the structure has been specifically observed. In all cases, the three sites can be occupied by both Ca2+ and RE3+, and the repartitions depend on the ionic radius of RE3+.
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