现代结构分析方法20097(免费阅读).pptVIP

现代结构分析方法(09－10年度第一学期) 第7讲 倒易点阵与正点阵 4，衍射几何条件：厄瓦球面 4，衍射几何条件：厄瓦球面 5 diffractometer (1/l)/ghkl＝L/Rhkl’ R’d = lL When is q small (electron diffraction), Rd=lL=diffraction constant 倒易点阵、正点阵与衍射 7 衍射图标定?相；取向7.1 单晶衍射图的产生与标定 When is q small (electron diffraction), Rd=lL=diffraction constant, the reflection sphere cuts a 2D reciprocal plane. Indexing: the plane normal [uvw] and at least one low index spot (hkl) (normally two spots), with hu+kv+lw=0. Plot the fcc [110] diffraction pattern 1) The zone axis [uvw] is perpendicular to all the plane indices (hkl) so that hu+kv+lw=0. 2) Distinctions of an fcc lattice: all even or odd (like 111, 200, 311, 220, etc.) 3) R1+R2=R3, and R1×R2=[UVW], R1 and R2 being the two short vectors 4) Fix R1 (if a and Ll are given then R1 is a known value) and draw R2, cosR1^R2=(h1*h2+k1*k2+l1*l2)/ (?N1?N2); R12/R22=N1/N2 5) All the other spots are determined by n1*R1+n2*R2=Rn Plot the fcc [-1-1-8] diffraction pattern 1) The zone axis [-1-1-8] is perpendicular to all the plane indices (hkl) so that hu+kv+lw=h*-1+k*-1+l*-8=0. 2) Distinctions of an fcc lattice: all even or odd (111, 200, 311, 220, 531 etc.) 3) R1+R2=R3, and R1×R2=[UVW], R1 and R2 being the two short vectors R1: 2-20; R2: -5-31; R3= R1+R2= -3-51 4) Fix R1-10 (arbitrary length) and draw R-5-31, cosR1-10^R-5-31 = (h1*h2+k1*k2+l1*l2)/ (?N1?N2)=103.83; R12/R22=N1/N2=8/35 5) All the other spots are determined by n1*R1+n2*R2=Rn Plot the bcc [345] diffraction pattern 1) The zone axis [345] is perpendicular to all the plane indices (hkl) so that hu+kv+lw=h*3+k*4+l*5=0. 2) Distinctions of an fcc lattice: 110, 200, 211, 220, 530 etc.) 3) R1+R2=R3, and R1×R2=[UVW], R1 and R2 being the two short vectors R1: 1-21; R2: -503; R3= R1+R2= -4-24 4) Fix R1-21 (arbitrary length) and draw R-503, cosR1-21^R-503 = (h1*h2+k1*k2+l1*l2)/ (?N1?N2)=98.05; R12/R22=N1/N2=6/34 5) All the other spots are determined by n1*R1+n2*R2=Rn Plot the [211] diffraction pattern of Fe3C (Pnma, a=0.50890, b=0.67433, c