抄録
We have prepared a new layered oxycarbide, [Al5.25(5)Si0.75(5)][O1.60(7)C3.40(7)], by isothermal heating of (Al4.4Si0.6)(O1.0C3.0) at 2273 K near the carbon-carbon monoxide buffer. The crystal structure was characterized using XRPD, TEM and EDX. The title compound is trigonal with space group R-3m, Z = 3, and a = 0.32464(2) nm, c = 4.00527(14) nm and V = 0.36556(3) nm3. The atom ratios Al : Si were determined by EDX, and the initial structural model was derived by the direct methods. The final structural model showed the positional disordering of one of the three types of Al/Si sites. The reliability indices were Rwp = 4.45% (S = 1.30), Rp = 3.48%, RB = 2.27% and RF = 1.25%. The crystal is composed of three types of domains with nearly the same fraction, one of which has the crystal structure of space group R-3m. The crystal structure of the rest two domains is noncentrosymmetric (R3m).
