2007年国家司法考试试卷一真题解析Tit.ppt

* Quasicrystals  AlCuLi QC Rhombic triacontrahedral grain Typical decagonal QC diffraction pattern (TEM) Quasicrystals  Diffraction pattern for 8-fold QC Diffraction pattern for 12-fold QC Quasicrystals  Principal types of QCs: icosahedral decagonal Quasicrystals  Principal types of QCs: icosahedral decagonal metastable (rapid solidifcation) stable (conventional solidification) Quasicrystals  Principal types of QCs: icosahedral decagonal metastable (rapid solidifcation) stable (conventional solidification) QCs usually have compositions close to crystalline phases - the crystalline approximants Quasicrystals   While pentagons (108° angles) cannot tile to fill 2=D space, two rhombs w/ 72° 36° angles can - if matching rules are followed N.B. - see definitive comprehensive book on tiling by Grünbaum and Shepherd Quasicrystals   While pentagons (108° angles) cannot tile to fill 2=D space, two rhombs w/ 72° 36° angles can - if matching rules are followed Quasicrystals   Fourier transform of this Penrose tiling gives a pattern which exhibits 5 (10) - fold symmetry – very similar to diffraction patterns for icosahedral QCs Quasicrystals   Quasicrystals   Quasicrystals   Diffraction pattern (in reciprocal space) of icosahedral QC can be indexed w/ 6 six integers - axes along 6 icosahedron directions qi (referred to Cartesian qx, qy, qz) 1 t Quasicrystals   Diffraction pattern (in reciprocal space) of icosahedral QC can be indexed w/ 6 six integers - axes along 6 icosahedron directions qi (referred to Cartesian qx, qy, qz) q1 = (1 t 0) q2 = (t 0 1) q3 = (t 0 1) q4 = (0 1 t) q5 = (1 t 0) q6 = (0 t 1) 1 t Quasicrystals   t = (1 + 5)2 = 1.618… Diffraction pattern (in reciprocal space) of icosahedral QC can be indexed w/ 6 six integers - axes along 6 icosahedron direc