Phase Relationships in the Silicon Carbide‐Aluminum Nitride System

Phase relationships in the SiC‐AlN system were determined by analytical electron microscopy of local equilibria among adjacent phases in hot‐pressed samples and in diffusion couples. At 2100° to 2300°C, a 4H–2H equilibrium exists, the 4H field extending from ∼2 mol% AlN to an upper limit of 11 to 14 mol% AlN. The wurtzite‐type 2H (δ) solid solution extends from an impurity‐sensitive lower limit of 17 to 24 mol% AlN up to 100 mol% AlN. Semiquantitative Auger electron spectroscopy and energy dispersive X‐ray spectroscopy ultrathin‐window detector measurements confirmed the assumption that the solid solutions have the general formula (SiC) 1‐x (AlN) x and belong to the SiC‐AlN pseudobinary system. The existence of a miscibility gap below 1950°C was confirmed, but its limits were not determined accurately. A faulted metastable cubic phase, β′, exists below ∼2000°C and contains up to ∼4 mol% AlN. The transformations into the stable a structures occur through diffusion‐controlled stacking rearrangements.