Fabrication of Novel Ceramics in the Rare-Earth Oxide and Silicon Nitride System and Their Evaluation for the Application to the Materials

作者在Si_3N_4-SiO_2-Y_2O_3系统中制备了四种陶瓷，即：黄长石型结构（Y_2Si_3O_3N_4）、硅灰石型结构（YSiO_2N）、尖晶石型结构（Y_4Si_2O_7N_2）和磷灰石型结构（Y_5（SiO_4）_3N），并对其热性能和力学性能进行了评价。研究了以Si_3N_4和RE_2O_3为原料合成RE_2Si_3O_3N_4（RE = La、Ce、Nd、Sm、Gd、Dy、Er和Yb）的工艺条件。采用热压工艺制备了Si_3N_4-SiO_2-Y_2O_3系高密度陶瓷。Si_3N_4-SiO_2-Y_2O_3系统热压陶瓷的相对密度在98%以上。抗弯强度的大小顺序为：YSiO_2N（249 MPa）> Y_2Si_3O_3N_4（193 MPa）> Y_4Si_2O_7N_2（177 MPa）> Y_5（SiO_4）_3N（144 MPa）。Y_2Si_3O_3N_4和YSiO_2N陶瓷分别在1100℃和1050℃左右开始氧化，Y_4Si_2O_7N_2陶瓷在800℃左右开始氧化，Y_5（SiO_4）_3N陶瓷在850℃左右开始氧化。以Si_3N_4和RE_2O_3为原料，研究了RE_2Si_3O_3N_4（RE =稀土金属）的合成条件。当RE = Nd，Sm，Gd，Dy和Er时，形成了单一的RE_2Si_3O_3N_4相。在这些化合物中，只有Gd_2Si_3O_3N_4在近紫外光照射下发光。在Gd_2Si_3O_3N_4中掺杂了激活剂RE ′_2O_3。Sm掺杂的Gd_2Si_3O_3N_4的激发峰位于300 nm，而发射峰位于601 nm。这种磷光体发出红光。随着Sm掺杂量的增加，Sm掺杂量为1mol%时，Gd_2Si_3O_3N_4的发光强度达到1.8。结果表明，在Si_3N_4-SiO_2-Y_2O_3系统的四种复合材料中，热压法制备的YSiO_2N陶瓷的抗弯强度最大（249 MPa），而Sm掺杂1mol%的Gd_2Si_3O_3N_4陶瓷的抗弯强度最大（相对强度为1.8）。

The author fabricated four kinds of ceramics in the Si_3N_4-SiO_2-Y_2O_3 system, i.e., melilite-type structure (Y_2Si_3O_3N_4), wollastonite-type structure (YSiO_2N), cuspidine-type structure (Y_4Si_2O_7N_2) and apatite-type structure (Y_5(SiO_4)_3N), and evaluated the thermal and mechanical properties. Moreover, synthesis conditions of RE_2Si_3O_3N_4 (RE = La, Ce, Nd, Sm, Gd, Dy, Er and Yb) were examined using Si_3N_4 and RE_2O_3. The high-density ceramics in the Si_3N_4-SiO_2-Y_2O_3 system were fabricated from the powders by hot pressing technique. Relative densities of the hot-pressed ceramics in the Si_3N_4-SiO_2-Y_2O_3 system were 98% or higher. The magnitude of the flexural strength of these ceramics could be arranged as follows; YSiO_2N(249 MPa) > Y_2Si_3O_3N_4(193 MPa) > Y_4Si_2O_7N_2(177 MPa) > Y_5(SiO_4)_3N(144 MPa). Oxidations of Y_2Si_3O_3N_4 and YSiO_2N ceramics started at around 1100℃ and 1050℃, respectively ; oxidation of Y_4Si_2O_7N_2 ceramic started at around 800℃, whereas that of Y_5(SiO_4)_3N ceramic started at around 850℃. Synthesis conditions of RE_2Si_3O_3N_4 (RE = rare-earth metal) were examined using Si_3N_4 and RE_2O_3. Single phases of RE_2Si_3O_3N_4 were formed in the case of RE = Nd, Sm, Gd, Dy and Er. Among these compounds, only Gd_2Si_3O_3N_4 emitted the light by the irradiation of near-ultraviolet beam. The activators (RE'_2O_3) were doped to the Gd_2Si_3O_3N_4. In the case of Sm-doped Gd_2Si_3O_3N4, the excitation peak appeared at 300 nm, whereas the emission peak appeared at 601 nm. This phosphor emitted the red light. With increasing amount of Sm dopant, the emission intensity of Gd_2Si_3O_3N4 with 1 mol% of Sm dopant achieved 1.8. It was concluded that among four kinds of the composites in the Si_3N_4-SiO_2-Y_2O_3 system, the flexural strengths of YSiO_2N ceramics fabricated by hot pressing-techniques showed maximum (249 MPa), whereas 1 mol% of Sm-doped Gd_2Si_3O_3N_4 intensity showed maximum (relative intensity:1.8).