HP-CaSiN2 was obtained by HP/HT (high pressure / high temperature) synthesis utilizing the multianvil technique (4.5 to 18 GPa, 900 to 1200 degrees C) starting from the ambient pressure phase CaSiN2. Structure solution and Rietveld refinement were started with the cell parameters of HP-CaSiN2 determined by selected area electron diffraction (SAED). The crystal structure of the high-pressure phase was refined in space group Pbca (no. 61) with a = 5.1296(2), b = 10.2993(2), c = 14.5442(3) angstrom, V = 768.39 angstrom(3), Z = 16, R-Bragg = 0.0484, R-w = 0.0256 and GoF = 1.0. HP-CaSiN2 is built up by a three-dimensional nitridosilicate network of vertex-sharing SiN4-tetrahedra with N bridging. The arrangement of the vertex-linked tetrahedra in HP-CaSiN2, being isostructural with KGaO2, is a tilting distortion of the stuffed -cristobalite type framework. Due to the high pressure the tilting angle of the SiN4-tetrahedra has become much smaller so that the latter appear edge-sharing sharing which is only a consequence of the chosen view along [100]. The Ca ions are located within these sechser-ring channels and are coordinated by 6 and 7 N-atoms, respectively. HP-CaSiN2 is similar to CaSiN2, but differs clearly in the rotation of the SiN4-tetrahedra and in the conformation of the sechser-rings. Because of their coexistence HP-CaSiN2 and CaSiN2 represent a very good example of an isosymmetric polymorphism.

中文翻译：

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HP-CaSiN2 - 一种新的高压改性

HP-CaSiN2 是从环境压力相 CaSiN2 开始，利用多砧技术（4.5 至 18 GPa，900 至 1200 摄氏度）通过 HP/HT（高压/高温）合成获得的。结构求解和 Rietveld 精修从通过选区电子衍射 (SAED) 确定的 HP-CaSiN2 的电池参数开始。高压相的晶体结构在空间群 Pbca (no. 61) 中精修，a = 5.1296(2), b = 10.2993(2), c = 14.5442(3) 埃, V = 768.39 埃(3) , Z = 16, R-Bragg = 0.0484, Rw = 0.0256 和 GoF = 1.0。HP-CaSiN2 由具有 N 桥接的顶点共享 SiN4-四面体的三维氮化硅酸盐网络构成。HP-CaSiN2 中顶点连接的四面体的排列，与 KGaO2 同构，是填充方石英型框架的倾斜变形。由于高压，SiN4-四面体的倾斜角变得更小，以至于后者出现边缘共享，这只是沿[100]选择视图的结果。Ca 离子位于这些 sechser-ring 通道内，分别由 6 个和 7 个 N 原子协调。HP-CaSiN2 类似于 CaSiN2，但在 SiN4-四面体的旋转和 sechser 环的构象方面明显不同。由于它们的共存，HP-CaSiN2 和 CaSiN2 代表了等对称多态性的一个很好的例子。Ca 离子位于这些 sechser-ring 通道内，分别由 6 个和 7 个 N 原子协调。HP-CaSiN2 类似于 CaSiN2，但在 SiN4-四面体的旋转和 sechser 环的构象方面明显不同。由于它们的共存，HP-CaSiN2 和 CaSiN2 代表了等对称多态性的一个很好的例子。Ca 离子位于这些 sechser-ring 通道内，分别由 6 个和 7 个 N 原子协调。HP-CaSiN2 类似于 CaSiN2，但在 SiN4-四面体的旋转和 sechser 环的构象方面明显不同。由于它们的共存，HP-CaSiN2 和 CaSiN2 代表了等对称多态性的一个很好的例子。