中文摘要：

为了研究 γ-Si3N4在高温高压下的相变，在压力为 5.2、5.4 及 5.7 GPa，温度为 1 300～1 450 K，保温时间为 15 min 条件下，以 Y2O3、Al2O3和 La2O3为烧结助剂，制备了 γ-Si3N4烧结体。用 X 射线衍射和扫描电子显微镜对烧结样品进行了分析和观察。结果表明：γ-Si3N4首先转变为 α-Si3N4，再由 α-Si3N4转变为 β-Si3N4；β-Si3N4烧结体主要由长柱状的晶粒组成，晶粒相互连接，呈交叉分布，显微结构较为均匀，结构致密。拟合了三相相界方程，得到了γ、γ＋α、α、α＋β、β-Si3N4相界方程，并讨论了相关的相变机制。

英文摘要：

In order to investigate the phase transition of γ-Si3N4 under high pressure and high temperature, γ-Si3N4 was sintered with Y2O3, Al2O3 and La203 as additives at 5.2, 5.4 and 5.7 GPa and 1 300-1 450 K for 15 min, respectively. The sintered samples were analyzed by X-my diffraction and scanning electron microscopy. The results show that the γ-Si3N4 powder is firstly transformed into α-Si3N4, and then α-Si3N4 is transformed into β-Si3N4. When the γ-Si3N4 powder was completely transformed into β-Si3N4, the sintered samples were mainly composed of the elongated rod crystals with the interconnected and cross distribution, and had the more uniformity and compact microstructure. The rough boundary equations of γ、γ＋α、α、α＋β and β could be used to fit the experimental data, respectively. In addition, the related mechanism of phase transformation was also discussed.