Formation behavior and microstructure of multi-cation α-sialons containing neodymium and ytterbium or yttrium

Multi-cation α-sialons containing neodymium and ytterbium, as well as neodymium and yttrium, were prepared by hot pressing at the temperatures ranging from 1550 to 1750°C for 2 h with the compositions (Nd0.18Yb0.18/Nd0.18Y0.18)Si10.36Al1.62O0.54N15.46. The densification process, reaction sequence, cell dimensions and microstructure were studied in comparison with the corresponding single cation α-sialon. Experimental results have shown that the samples hot-pressed at 1750°C mainly consist of α-sialon phase, whose content (around 95 wt%) is higher than that of counterpart single rare earth doped α-sialon, especially much higher than the one of Nd-α-sialon. On the other hand, the multi-cation α-sialons compositions are beneficial to lower the eutectic temperature in the systems, thus promoting the dissolution of intergranular crystalline melilite phase, and facilitating the precipitation of α-sialon phase. TEM and EDS revealed that the amount of Yb3+ or Y3+, which possess relatively smaller ionic radii than Nd3+, is higher than that of the Nd3+ in α-sialon grains and more Nd3+ are remained in the grain boundary phase. Small amount of elongated α-sialon grains were observed by TEM and the preferred orientation also occurred under hot-pressing for such a low x value composition (x=0.36) used in this study.