Synthesis and crystal structure refinement by the Rietveld method of antimony-bearing titanite Ca(Ti_(0.6)Al_(0.2)Sb_(0.2))OSiO_4

摘要

A synthetic analogue, Ca(Ti_(0.6)Al_(0.7)Sb_(0.2))OSiO_4, of antimony-bearing titanite of a composition similar to that found at St. Marcel-Praborna (Italy) was synthesized using ceramic methods and the crystal structure was refined using the Rietveld method. Unit-cell dimensions (in A) are a = 7.0184(1), b = 8.7097(2), c = 6.5586(1), and β=113.700(1)°. The substitution of 40% Ti by (Al + Sb) in octahedra causes a loss of long-range coherency of the off-centered Ti atoms. The space group of Sb-bearing titanite is All a, like other cases of M~(3+)-M(5+)-doped titanites. This study confirms that titanite with up to 0.2 Sb atom per f.u. can exist and that the substitution scheme is 2Ti~(4+)←→Al~(3+)+Sb~(5+).