Synthesis and structural characterization of Al7C3N3-homeotypic aluminum silicon oxycarbonitride, (Al7-xSix)(OyCzN6-y-z) (x∼1.2, y∼1.0 and z∼3.5)

A new aluminum silicon oxycarbonitride, (Al5.8Si1.2)(O1.0C3.5N1.5), has been synthesized and characterized by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). The title compound is hexagonal with space group P63/mmc and unit-cell dimensions a=0.322508(4) nm, c=3.17193(4) nm and V=0.285717(6) nm3. The atom ratios of Al:Si and those of O:C:N were, respectively, determined by EDX and EELS. The initial structural model was successfully derived from the XRPD data by the direct methods and further refined by the Rietveld method. The crystal is most probably composed of four types of domains with nearly the same fraction, each of which is isotypic to Al7C3N3 with space group P63mc. The existence of another new oxycarbonitride (Al6.6Si1.4)(O0.7C4.3N2.0), which must be homeotypic to Al8C3N4, has been also demonstrated by XRPD and TEM. - Graphical abstract: A new oxycarbonitride discovered in the Al-Si-O-C-N system, (Al7-xSix)(OyCzN6-y-z) (x∼1.2, y∼1.0 and z∼3.5). The crystal is composed of four types of domains (I, II, III and IV), and hence the structure is represented by a split-atom model. Individual crystal structures can be regarded as layered structures, which consist of A-type [(Al, Si)4(O, C, N)4] unit layers and B-type [(Al, Si)(O, C, N)2] single layers. Highlights: → (Al5.8Si1.2)(O1.0C3.5N1.5) as a new aluminum silicon oxycarbonitride. → Crystal structure is determined and represented by a split-atom model. → Existence of another new oxycarbonitride (Al6.6Si1.4)(O0.7C4.3N2.0) is demonstrated. → Both new materials are formed by oxidation and nitridation of (Al, Si)6(O, C)5.