High thermal conductivity Si_3N_4 ceramic is a prospective substrate material for high-power electronic devices. In this paper, pressureless and liquid-phase sintering was proposed using Re_2 O_3(Re=Sm, Er, Lu)-Ti O_2 as sintering additives to effectively reduce the cost for applications. Effect of the additive type and content on microstructure, mechanical properties and thermal conductivity of the ceramic were investigated. Results showed that the relative density, thermal conductivity and grain size of S...