The crystal structure of 6 Ca2SiO4·1 Ca3(PO4)2

Single crystals of the composition 6 Ca2SiO4 · 1 Ca3(PO4)2 have been grown by the Verneuil-method. The crystals represent a structure derivative of α′-Ca2SiO4. Due to twinning of the crystals a structure determination was possible only on the basis of the weak superlattice reflections [Pnm21; a = 9.40(8), b = 21.71(2), c = 6.83(3) Å, Z = 2]. Important features are: (1) All tetrahedra are tilted away from the ideal positions, (2) there is no strong ordering nor statistic distribution of Si, P, Ca, (3) there exists a relation between the tetrahedra positions enriched in P and the occupancies of the neighbouring Ca positions. (4) In reality the superlattice reflections proved to be satellites suggesting a modulated structure.