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crystal data
Indexed powder diffraction data are presented for Ca3Al2O6 and its sodium-containing solid solutions. Powder patterns of the cubic and orthorhombic phases calculated from the crystal structure data are compared with the observed patterns. Indexed data are presented for the monoclinic phase, which is stabilized by sodium and silicon. The so-called tetragonal phase is shown by electron diffraction to be orthorhombic, pseudo-tetragonal. It probably has the symmetry Pcaa with a = b = 10.8599 (9), c = 15.1234 (20) Å.