《材料科学与工程基础》英文影印版习题及思考(7)

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3.25 For a ceramic compound, what are the two characteristics of the component ions

that determine the crystal structure?

3.29 On the basis of ionic charge and ionic radii, predict the crystal structures for the

following materials: (a) CsI, (b) NiO, (c) KI, and (d) NiS. Justify your selections.

3.35 Magnesium oxide has the rock salt crystal structure and a density of 3.58 g/cm3.

(a) Determine the unit cell edge length. (b) How does this result compare with the edge length as determined from the radii in Table 3.4, assuming that the Mg2_ and O2_ ions just touch each other along the edges?

3.36 Compute the theoretical density of diamond given that the CUC distance and

bond angle are 0.154 nm and 109.5°, respectively. How does this value compare with the measured density?

3.38 Cadmium sulfide (CdS) has a cubic unit cell, and from x-ray diffraction data it is

known that the cell edge length is 0.582 nm. If the measured density is 4.82 g/cm

—3 , how many Cd 2+ and S 2 ions are there per unit cell?

3.41 A hypothetical AX type of ceramic material is known to have a density of 2.65

g/cm 3 and a unit cell of cubic symmetry with a cell edge length of 0.43 nm. The atomic weights of the A and X elements are 86.6 and 40.3 g/mol, respectively. On the basis of this information, which of the following crystal structures is (are) possible for this material: rock salt, cesium chloride, or zinc blende? Justify your choice(s).

3.42 The unit cell for Mg Fe2O3 (MgO-Fe2O3) has cubic symmetry with a unit cell

edge length of 0.836 nm. If the density of this material is 4.52 g/cm 3 , compute its atomic packing factor. For this computation, you will need to use ionic radii listed in Table 3.4.

3.44 Compute the atomic packing factor for the diamond cubic crystal structure

(Figure 3.16). Assume that bonding atoms touch one another, that the angle between adjacent bonds is 109.5°, and that each atom internal to the unit cell is positioned a/4 of the distance away from the two nearest cell faces (a is the unit cell edge length).

3.45 Compute the atomic packing factor for cesium chloride using the ionic radii in

Table 3.4 and assuming that the ions touch along the cube diagonals.

3.46 In terms of bonding, explain why silicate materials have relatively low densities.

3.47 Determine the angle between covalent bonds in an SiO44— tetrahedron.

3.63 For each of the following crystal structures, represent the indicated plane in the

manner of Figures 3.24 and 3.25, showing both anions and cations: (a) (100)