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* LOGO * The 14 possible BRAVAIS LATTICES {note that spheres in this picture represent lattice points, not atoms!} 2. 晶体结构与空间点阵-C 7 crystal Classes Crystal system Unit cell shape Essential symmetry Space lattices Cubi a=b=c a=b=g=90 Four threefold axes P I F Tetragonal a=b≠c a=b=g=90 One fourfold axis P I Orthorhombic a≠b≠c a=b=g=90 Three twofold axes or mirror plane P I F A(B or C) Hexagona A=b≠c a=g=90 b=120 One threefold axis P Trigonal A=b≠c a=g=90 b=120 One threefold axis P a=b=c a=b=g≠90 One threefold axis R Monoclinic a≠b≠c a=b=90 g≠90 One twofold axis or mirror plane P C Triclinic a≠b≠c a≠b≠g≠90 none P 2. 晶体结构与空间点阵-D 点阵类型 ◆阵点的坐标表示 ●以任意顶点为坐标原点，以与原点相交的三个棱边为坐标轴，分别用点阵周期（a、b、c）为度量单位 四种点阵类型 简单 体心 面心 底心 ◆简单点阵的阵点坐标为000 ◆底心点阵，C 除八个顶点上有阵点外，两个相对的面心上有阵点，面心上的阵点为两个相邻的平行六面体所共有。因此，每个阵胞占有两个阵点。阵点坐标为