The peaks for δ-TaN are weak and broad, indicating the small size of its particles. The lattice parameter calculated from the highest intensity BMN-673 peak (111) was a = 4.32 Å. This was in good agreement with the previously reported value of 0.433 ± 0.001 nm for thin films [17].

The nitrogen content in the powders at various k values is shown in Table 1. It shows that the nitrogen content at k = 0 is 7.01%, which corresponds to the TaN0.98 composition. With increasing k, the nitrogen content then slowly drops down, reaching to 6.51% at k = 4. This amount of nitrogen theoretically corresponds to the TaN0.91 composition. All the powders contain about 0.15% carbon. Figure 6 XRD patterns of water-purified powders synthesized from K 2 TaF 7 + (5 + k )NaN 3 + k NH 4 F mixture. (a) k = 0, (b) k = 2.0, and (c) k = 4.0. Table 1 Content of nitrogen in TaN k (mol) N (%) Formula 0 7.01 TaN0.98 2 6.95 TaN0.97 3 6.72 TaN0.94 4 6.51 TaN0.91 RAAS inhibitor The SEM microstructure of the combustion product (k = 0) right after the synthesis process is shown in Figure 7a.

Due to a large portion of ERK inhibitor molten fluorides (5NaF to 2KF), the final product has a molten microstructure in which the crystalline particles of tantalum nitride are embedded. The microstructure of the same sample after water purification is shown in Figure 7b. A part of TaN particles were crystallized in a rodlike fashion; at that, the length of rods is about 0.5 to 1.5 μm, as estimated from the micrograph. A large portion of small particles whose sizes are on the order of submicrometers also exist on the same micrograph. We think that the presence of different-sized particles in Figure 7b can be associated with the phase composition of the product, i.e., the rod-shaped particles most likely are those of hexagonal ε-TaN, whereas the small-sized particles belong to the TaN0.8 and Ta2N phases. With an increase in k, the rod-shaped particles disappeared, and the size of particles became smaller and uniform. As a typical example, the micrograph Oxalosuccinic acid of the cubic δ-TaN particles produced using 4.0 mol of NH4F is shown in

Figure 7c. These particles are less than 100 nm in size. They usually exist in the form of relatively large clusters (0.5 to 1.0 μm), owing to the attractive forces between the particles. EDS analysis taken from rodlike and small-sized particles (Figure 7b,c) shows Ta and N as the main elements; however, small peaks of oxygen also exist. Figure 7 SEM micrographs of reaction product (a), and water-purified TaN samples with EDX analysis (b, c). (a) k = 0, (b) k = 0, and (c) k = 4. Figure 8a shows the TEM image and the corresponding selected area electron diffraction (SAED) pattern of the cubic δ-TaN nanoparticles synthesized at 800°C from the K2TaF7 + 9NaN3 + 4NH4F mixture. The TEM image confirmed the formation of TaN nanoparticles, which had an average size of <10 nm.