Synthesis and structural characterisation of new ettringite and thaumasite type phases: Ca-6[Ga(OH)(6)center dot 12H(2)O](2)(SO4)(3)center dot 2H(2)O and Ca-6[M(OH)(6)center dot 12H(2)O](2)(SO4)(2)(CO3)(2), M = Mn, Sn

Investigations into the formation of new ettringite-type phases with a range of trivalent and tetravalent cations were carried out to further study. the potential this structure type has to incorporate cations covering a range of ionic radii (0.53-0.69 angstrom). We report the synthesis and structural characterisation of a new ettringite-type phase, Ca-6[Ga(OH)(6)center dot 12H(2)O](2)(SO4)(3)center dot 2H(2)O, which was indexed in space group P31c with the unit cell parameters a = 11.202(2) angstrom, c = 21.797(3) angstrom and two new thaumasite-type phases Ca-6[M(OH)(6)center dot 12H(2)O](2)(SO4)(2)(CO3)(2), M = Mn, Sn which were indexed in space group P63 with the unit cell parameters a = 11.071(5) angstrom, c = 21.156(8) angstrom and a = 11.066(1) angstrom, c = 22.420(1) angstrom respectively. These new phases show the versatility of the ettringite family of structures to tolerate a large range of cation sizes on the octahedral M site and highlights the preference of tetravalent cations to crystallise with the thaumasite structure over the ettringite structure. (C) 2013 Elsevier Masson SAS. All rights reserved.