镶嵌晶体是C.G.Darwin在1922年提出的真实晶体的简化模型（The reflection of X-rays from imperfect crystals. Philos. Mag. 43, 809–829；但“镶嵌”一词实际上是由P.P.Ewald引入的）。在这个模型中，真实的晶体被描述为微小晶体块体的组合体，彼此倾斜很小的角度。每个微小晶体都被断层和裂缝与周围的微小晶体隔开。在衍射实验中，波之间的干涉只发生在块体内部，其尺寸满足运动学理论适用的理论条件。由于从不同块衍射的波之间的相干性损失，来自整个晶体的衍射强度等于每个块衍射的强度之和。如果块不够小，则在每个块内都会发生动力学效应，从而降低衍射强度。这是初级消光。如果块体相对于彼此的取向不充分，则衍射强度也会降低。这是二次消光。The mosaic crystal is a simplified model of real crystals proposed by C. G. Darwin in 1922 (The reflection of X-rays from imperfect crystals. Philos. Mag. 43, 809–829; but the term 'mosaic’ was actually introduced by P. P. Ewald). In this model, a real crystal is described as a conglomerate of minute crystalline blocks, tilted to each other by fractions of a minute of arc. Each block is separated from the surrounding blocks by faults and cracks.In a diffraction experiment, interference between waves only occurs inside a block, whose dimensions satisfy the theoretical conditions of applicability of the kinematical theory. Because of the loss of coherence between the waves diffracted from different blocks, the diffracted intensity from the whole crystal is equal to the sum of the intensities diffracted by every block. If the blocks are not small enough, dynamic effects take place within each block, reducing the diffracted intensity. This is primary extinction. If the blocks are not sufficiently misoriented with respect to each other, reduction of the diffracted intensity also occurs. This is secondary extinction.![]()
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