中文摘要：

采用反应烧结工艺,通过添加硬脂酸,制备孔径为0.8 mm,孔隙率在55%左右的具有宏观球形孔的低密度多孔氮化硅陶瓷,研究了α/β相变对多孔氮化硅陶瓷介电性能的影响。通过调节氮化温度和时间,可得到具有不同β相相对含量（质量分数,下同）的多晶氮化硅陶瓷。结果表明：氮化温度高于1 400℃时发生α/β相变,随着氮化温度的提高和时间的延长,β相的相对含量增加,氮化硅的微观形貌也发生明显变化,由针状和絮状形貌转变成片状形貌最后形成长柱状结构。α/β相变使样品的相对介电常数ε′和介电损耗tanδ都呈现升高的趋势,其中tanδ的变化更为明显。相变导致的氮化硅陶瓷中点缺陷浓度增高是引起材料介电损耗大幅增加的主要原因。

英文摘要：

Low-density porous silicon nitride ceramics,which contained 0.8 mm spherical pores in diameter and had porosity of about 55%,were prepared through adding stearic acid by reactive sintering.The influence of α/β phase transformation on the dielectric properties of porous silicon nitride ceramics was investigated.Pleomorphic silicon nitride ceramics with different relative content（in mass,the same below） of β phase were obtained by setting the nitriding temperature and time.The results show that the α/β trans-formation occurs when the nitriding temperature is higher than 1 400 ℃.The relative content of the β phase increases and the mor-phologies changes from an equiaxed shape to prismatic one with the increase of nitriding temperature and time.The dielectric con-stant ε′ and the dielectric loss tan δ of the samples increase because of the α/β transformation,and the change of the dielectric loss is more obvious.The increase of concentration of point defects due to the α/β transformation leads to the significant increase of the dielectric loss.