→Octahedron Connectivity →Edge sharing octahedra 4 NaCl in unit cell. • Structure of NaCl CERAMIC STRUCTURE (1) This structure can be described as having FCC Bravais lattice with two ions (1Na+ and 1Cl-) ... • The unique relationship between such patterns and crystal structures provide a powerful tool for identification of the phase composition of powders and polycrystalline materials. First, consider examples of crystals with a basis group of just one atom per lattice point, with atomic scattering factor f. The results are valid for any crystal system. We can specify the structure of cesium chloride, for example, with only four pieces of 12.3, Callister 7e. 939 0. N = 1, so n 1 (The text is taken from: Basic Solid State Chemistry, by Anthony R. West) 1.17 Some important structure types a) Rock salt (NaCl), zinc blende or sphalerite (ZnS), fluorite (CaF2), antifluorite (Na2O) These structures are considered together because they all have ccp/fcc anions and differ only in the positions of the cations. The calcite (CaCO 3) crystal structure is shown above.Triangular CO 3 2-ions fill octahedral holes between the Ca 2+ ions (black spheres) in a distorted NaCl lattice. CsCl •Thinking about the unit cell as a three-dimensional graph allows us to describe the structure of a crystal with a remarkably small amount of information. As in NaCl, each ion is coordinated by six of the other kind. determining crystal structures beginning with NaCl, ZnS and diamond. • All of the faces of the sodium chloride crystal are square, but can have different number of ions: 4 (2 x 2 x 2), 9 (3 x 3 x 3), and one Cl ion. Primitive Cells This is really simple! For example in NaCl, the basic building block is composed of one Na and one Cl ion which is repeated in a cubic pattern to make the NaCl structure 2 The Bravais lattice of NaCl is FCC with the basis containing one Na ion. Cesium Chloride structure: ∴ cubicsites preferred So each Cs + has 8 neighboring Cl- The molecule is under equilibrium because, the attractive force due to ions is balanced by repulsive force due to electron clouds. • Both the sodium chloride crystal and water crystal consist of repeating patterns. Differences • The sodium chloride crystal is a cube. ... NaCl Structure CCP with all octahedral holes filled Coordination= 6, 6 Cation Coord. NaCl (salt shaker variety) Hexagonal Close Packed: unit cell. →Octahedron Anion Coord. 1we will see that the basic building blocks of periodic structures can be more complicated than a single atom. • Ittellsuswhichreflections(ie peaksIt tells us which reflections (i.e., peaks , hkl)to) to expect in a diffraction pattern. Zinc Blende (ZnS) Structure structure. • The water crystal is a hexagon. Crystal Structures Chapter 7 Wednesday, October 21, 2015. Crystal Structure of Sodium Chloride(NaCl) NaCl is a ionic compound. Although Bragg's law was used to explain the interference pattern of X-rays scattered by crystals, diffraction has been . Structure Factor The general expression for : Now we apply this to various crystals. 181 0. 170 Cl Cs = = − + r r Adapted from Fig. AX Crystal Structures AX–Type Crystal Structures include NaCl, CsCl, and zinc blende 0. Structure Factor (Fhkl) 2( ) 1 ij i N ihu kv lw hkl i i Ffe • Describes how atomic arrangement (uvw) influences the intensity of the scattered beam. From this image we can see why the CaCO 3 structure has a lower symmetry than that of NaCl. Hence both Na and Cl are in ionic state.