FIGURE 3 (a) XRD pattern of the dark grey AlN powder sample; (b) and (c) Differentiating-imitations of the diffraction peaks situated at 2θ =32.4º-34º and 37-39.2º, respectively
To determine the phase composition of the dark grey AlN powder sample, an XRD analysis of the sample was performed, and the results are shown in Figure 3a. The main phase of the dark grey AlN powder sample is AlN. However, 2θ values of the three strong peaks of the AlN phase in Figure 3a were shifted left by 0.01-0.02º, comparing with the standard XRD pattern of AlN (PDF65-3409). This indicates that diffraction peak overlapping of AlN and other phases may occur. In fact, the diffraction peaks of Al2OC (100) (2θ = 33.13º) and Al2OC (101) (2θ = 37.80º) are very close to those of AlN(100) and (101) with a slight leftward shift. Therefore, it was predicted that the AlN diffraction peaks in Figure 3a were constructed by the diffraction peaks of AlN and Al2OC. Accordingly, taking the strongest peak (2θ = 33.25º) and second-strongest peak (2θ = 37.97º) in Figure 3a as examples, two differentiated and imitated diffraction peaks, referring to the AlN and Al2OC (100) and (101) planes, are shown in Figure 3b and c, respectively. Since the intensity of the AlN diffraction peak is so high and that of the Al2OC diffraction peak is so weak in Figure 3b and c, the Al2OC in the dark grey AlN powder sample is a low-concentration impurity phase.