材料分析方法-X射线衍射方向晶体学基础精要.ppt

第二章 X射线衍射方向河北工业大学材料学院孙继兵 E-mail: hbgdsjb@ 第二章 X射线衍射方向?第一节晶体学基础第一节晶体学基础?晶体特性?晶体结构与空间点阵?倒易点阵 1. 晶体性质?均匀性: 晶体内部各个部分的宏观性质是相同的。?各向异性: 晶体种不同的方向上具有不同的物理性质。?固定熔点: 晶体具有周期性结构,熔化时,各部分需要同样的温度。?规则外形: 理想环境中生长的晶体应为凸多边形。?对称性: 晶体的理想外形和晶体内部结构都具有特定的对称性。邻苯二甲酸氢刚玉电气石锗酸铋 2. 晶体结构与空间点阵-A(术语回顾) ?晶体(crystal) It is solid. The arrangement of atoms in the crystal is periodic. ?点阵(Lattice ) An infinite array of points in space, in which each point has identical surroundings to all others. ?晶体结构(Crystal Structure ) It can be described by associating each lattice point with a group of atoms called the MOTIF (BASIS ) ?单位晶胞( Unit Cell )The ponent of the crystal, which when stacked together with pure translational repetition reproduces the whole crystal ?晶胞参数 Unit Cell Dimensions a , b and c are the unit cell edge lengths. ???????, ? and ? are the angles ( ? between b and c, ? between c and a , ???? between a and b c .) 晶向和晶面指数 -B ?等同点与结点?结构基元:原子、分子或其集团?晶体结构=空间点阵+结构基元 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 Cubic a=b=c?=?= ???? Four threefold axes P I F Tetragona l a=b≠c?=?= ???? One fourfold axis P I Orthorhom bic a≠b≠c?=?= ???? Three twofold axes or mirror plane P I F A(B or C) Hexagona A=b ≠c ??????????????? One threefold axis P Trigonal A=b ≠c ??????????????? One threefold axis P a=b=c?=?=?≠??One threefold axis R Monoclinic a≠b≠c ??????????≠?? One twofold axis or mirror plane P C Triclinic a≠b≠c?≠?≠?≠?? none P