Chapter 12: Problem 28
Would you expect Frenkel defects for anions to exist in ionic ceramics in relatively large concentrations? Why or why not?
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Chapter 12: Problem 28
Would you expect Frenkel defects for anions to exist in ionic ceramics in relatively large concentrations? Why or why not?
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The unit cell for \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) has hexagonal symmetry with lattice parameters \(a=0.4961 \mathrm{~nm}\) and \(c=1.360 \mathrm{~nm}\). If the density of this material is \(5.22 \mathrm{~g} / \mathrm{cm}^{3}\), calculate its atomic packing factor. For this computation assume ionic radii of \(0.062 \mathrm{~nm}\) and \(0.140 \mathrm{~nm}\), respectively, for \(\mathrm{Cr}^{3+}\) and \(\mathrm{O}^{2-}\).
Using the Molecule Definition Utility found in both "Metallic Crystal Structures and Crystallography" and "Ceramic Crystal Structures" modules of \(V M S E\), located on the book's web site [www.wiley.com/ college/callister (Student Companion Site)], generate (and print out) a three-dimensional unit cell for titanium dioxide, \(\mathrm{TiO}_{2}\), given the following: (1) The unit cell is tetragonal with \(a=0.459 \mathrm{~nm}\) and \(c=0.296 \mathrm{~nm},(2)\) oxygen atoms are located at the following point coordinates: \(\begin{array}{llllll}0.356 & 0.356 & 0 & 0.856 & 0.144 & \frac{1}{2} \\\ 0.664 & 0.664 & 0 & 0.144 & 0.856 & \frac{1}{2}\end{array}\) and (3) Ti atoms are located at the following point coordinates: \(\begin{array}{llllll}0 & 0 & 0 & & 1 & 0 & 1 \\ 1 & 0 & 0 & & 0 & 1 & 1 \\\ 0 & 1 & 0 & & 1 & 1 & 1 \\ 0 & 0 & 1 & & \frac{1}{2} & \frac{1}{2} & \frac{1}{2} \\ 1 & 1 & 0 & & & & \end{array}\)
Compute the atomic packing factor for cesium chloride using the ionic radii in Table \(12.3\) and assuming that the ions touch along the cube diagonals.
Determine the angle between covalent bonds in an \(\mathrm{SiO}_{4}^{4-}\) tetrahedron.
Compute the atomic packing factor for the diamond cubic crystal structure (Figure 12.15). Assume that bonding atoms touch one another, that the angle between adjacent bonds is \(109.5^{\circ}\), 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).
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