Synthesis and structural characterisation of new ettringite and thaumasite type phases: Ca_6[Ga(OH)_6?12H_2O]_2(SO_4)_3?2H_2O and Ca_6[M(OH)_6?12H_2O]_2(SO_4)_2(CO_3)_2, M = Mn, Sn N^Rachel L NormanDepartment of Chemistry, Loughborough University, Loughborough LEU 3TU, UK

摘要

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 A). We report the synthesis and structural characterisation of a new ettringite-type phase,Ca_6[Ga(OH)_6?12H_2O]_2(SO_4)_3?2H_2O, which was indexed in space group P31c with the unit cell parameters a = 11.202(2) A, c = 21.797(3) A and two new thaumasite-type phases Ca_6[M(OH)_6?12H_2O]_2(SO_4)_2(CO_3)_2, M = Mn, Sn which were indexed in space group P63 with the unit cell parameters a = 11.071(5) A, c = 21.156(8) A and a = 11.066(1) A, c = 22.420(1) A 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.