抄録
A quaternary oxycarbide, [Al16.77(5)Si1.23(5)]Σ18[O3.04(9)C10.96(9)]Σ14, has been for the first time discovered in the Al-Si-O-C system. The crystal
structure was characterized by XRPD, TEM and EDX. The atom ratios [Al : Si] were determined by EDX, and the initial structural model was derived
by the direct methods. The structural parameters as well as the atom ratios [O : C] were determined by the Rietveld method. The crystal is monoclinic
(space group C2/m, Z = 1) with lattice dimensions a = 0.57404(1) nm, b = 0.331435(5) nm, c = 1.92410(2) nm, β = 90.036(1)º and V = 0.366076(9) nm3.
The final structural model showed the positional disordering of Al/Si sites. The validity of the split-atom model was verified by the three-dimensional
electron density distribution, the structural bias of which was reduced as much as possible using the maximum-entropy methods-based pattern fitting
(MPF). The reliability indices calculated from the MPF were Rwp = 4.20% (S = 1.14), Rp = 3.09%, RB = 0.92% and RF = 1.05%. The crystal was an
inversion twin with nearly the same twin fraction.
