Problem 1
Explain what is meant by (a) a Schottky defect in \(\mathrm{CaCl}_{2}\) and (b) a Frenkel defect in AgBr. (c) Suggest what effect doping crystals of AgCl with \(\mathrm{CdCl}_{2}\) might have on the AgCl lattice structure.
Problem 2
Why are \(d\) -block metal oxides much more frequently nonstoichiometric than are non-d-block metal oxides?
Problem 4
Comment on cach of the following: (a) the difference between extrinsic and intrinsic defects; (b) why \(\mathrm{CaO}\) is added to \(\mathrm{ZrO}_{2}\) used in refractory materials; (c) the formation of solid solutions of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) and \(\mathrm{Cr}_{2} \mathrm{O}_{3}\)
Problem 5
Suggest why doping \(\mathrm{NiO}\) with \(\mathrm{Li}_{2} \mathrm{O}\) in air (or the presence of \(\mathrm{O}_{2}\) ) leads to an increase in electrical conductivity, and comment on the dependence of this increase on the amount of lithium dopant.
Problem 7
If Ag electrodes are placed in contact with and on either side of a piece of bulk \(\mathrm{AgI}(\mathrm{mp} 831 \mathrm{K})\) heated at \(450 \mathrm{K}\) and current is passed through the cell for a given period, it is found that one electrode gains mass and the other loses mass. Rationalize these observations.
Problem 11
(a) The structure of \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}\) can be described as consisting of rock salt and perovskite layers. Describe the origin of this description. (b) Why is the potential replacement of NbTi by high-temperature superconducting components in M RI equipment of commercial interest?
Problem 14
Suggest likely products in the following reactions; (the reactions as shown are not necessarily balanced): (a) \(x \mathrm{LiI}+\mathrm{V}_{2} \mathrm{O}_{5} \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{CaO}+\mathrm{WO}_{3} \stackrel{\Delta}{\longrightarrow}\) (c) \(\mathrm{SrO}+\mathrm{Fe}_{2} \mathrm{O}_{3} \stackrel{\Delta, \text { in }}{\longrightarrow}\) \(O_{2}\)
Problem 15
Suggest possible solid state precursors for the formation of the following compounds by pyrolysis reactions: (a) \(\mathrm{BiCaVO}_{5} ;(\mathrm{b})\) the Mo(VI) oxide \(\mathrm{CuMo}_{2} \mathrm{YO}_{8}\) (c) \(\mathrm{Li}_{3} \ln \mathrm{O}_{3} ;(\mathrm{d}) \mathrm{Ru}_{2} \mathrm{Y}_{2} \mathrm{O}_{7}\)
Problem 17
Briefly discuss each of the following. (a) Precursors for, and composition and uses of, CVD wear-resistant coatings. (b) The production of GaAs thin films. (c) The advantages of using LEDs over traditional glass-reflector cat's eyes for road-lane markings. (d) Problems in developing CVD methods for the deposition of perovskite and cuprate superconductors.
Problem 20
(a) \(\mathrm{MOCVD}\) with \(\mathrm{Al}\left(\mathrm{O}^{\mathrm{i}} \mathrm{Pr}\right)_{3}\) as the precursor can be used to deposit \(\alpha\) -Al \(_{2} \mathrm{O}_{3}\). Outline the principle of MOCVD, commenting on the required properties of the precursors. (b) Fibres of InN can be grown at \(476 \mathrm{K}\) by the following reaction; nano-sized metal droplets act as catalytic sites for the formation of the crystalline fibres. \\[ \begin{aligned} 2 \mathrm{H}_{2} \mathrm{NNMe}_{2}+\operatorname{In}^{\mathrm{t}} \mathrm{Bu}_{2}\left(\mathrm{N}_{3}\right) & \\ &-\operatorname{InN}+2 \mathrm{Me}_{2} \mathrm{NH}+2^{\mathrm{t}} \mathrm{BuH}+2 \mathrm{N}_{2} \end{aligned} \\] When \(^{\prime} \mathrm{Bu}_{3}\) In replaces \(\operatorname{In}^{\prime} \mathrm{Bu}_{2}\left(\mathrm{N}_{3}\right),\) only amorphous products and metallic In are obtained. What is the likely role of the \(1,\) 1-dimethylhydrazine in the reaction, and what appears to be the primary source of nitrogen for the InN? Group 13 nitrides have applications in blue/violet LED displays. What controls the wavelength of emitted light in compounds of this type?
