Current interest in silicon nitride ceramics, a kind of high-temperature structurematerials, started more than 30 years ago, but the exact nature of the α→βtransformation in hot-pressed silicon nitride has not been completely understood. Be-cause it has been found that oxide additives are usually necessary to preparing siliconnitride ceramics of high quality, it is meaningful and important to investigate the diffusion behavior of additive ions in hot-pressed silicon nitride in order to have a bet-ter understanding of the process of the α→β phase transformation. Current interest in silicon nitride ceramics, a kind of high-temperature structurematerials, started more than 30 years ago, but the exact nature of theα → βtransformation in hot-pressed silicon nitride has not been completely understood. Be-cause it has been found that oxide additives are usually necessary to preparing siliconnitride ceramics of high quality, it is meaningful and important to investigate the diffusion behavior of additive ions in hot-pressed silicon nitride in order to have a bet-ter understanding of the process of the α → β phase transformation.