Page 79 - Materials Chemistry, Second Edition

66 2 Solid-State Chemistry

Figure 2.39. 2-D representations of the Pmm2, Amm2, Cmm2, Imm2 and Fmm2 space groups, showing
general positions and symmetry elements.

beam will be diffracted by the 3-D periodic array of atoms/ions to yield a
characteristic diffraction pattern on a photographic film or area detector/CCD camera
(Figure 2.40). As first presented in the early 1900s the most intense diffraction peaks
correspond to scattered waves that are in-phase with one another (i.e., constructive
interference), which will occur only when the conditions of the Bragg equation are
satisfied (Eq. 10 and Figure 2.41).