2004. 6.18
1.Provide a systematic account of the structural chemistry of perovskites and
perovskite-related compounds. You may find it useful to discuss some of the
following:
(i)Give a basic description of the two types of unit cells of perovskite
(ii)the importance of the tolerance factor in determining the structure of
compounds with stoichiometry ABX3
(iii)ordered oxygen vacancies in perovskite-like phases:the structures of
tetragonal YBa2Cu3O7-x
(20%)
2.(i)Name four types of crystal defects present in close packed metallic
systems as obtained, for example, by casting.
(ii)Which of these defects can be avoided if the solid phase is a perfect
single crystal?
(iii)Which defect is primarily responsible for the fact that metals do not
exhibit their theoretical tensile strength?
(iv)Which defect accounts for the phenomenon of Solid state diffusion in
these closed packed systems?
(20%)
3.Consider a spherical gold nanoparticle that is 3nm in diameter. If the
diameter of an atom is approximately 3A, how many atoms are on the surface
of the particle? What fraction of the gold atoms in the particle are on the
surface?
(12%)
4.(i)Skecth diagrams to illustrate the fundamental differences in band
structure between an insulator, a semiconductor, and a metal. By
annotating your diagrams, or otherwise, indicate the effacts of
temperature on electrical conduction for each type of material.
(ii)Explain the following terms:
a.Direct band gap semiconductor
b.Chemical Mechanical Polishing
c.Epitaxial growth
d.Ion Implantation
(20%)
5.The oxides MnO and NiO all have the cubic rock salt structure with
octahedral coordination of the cations. The structure of CuO is different
and contains grossly distorted CuO6 octahetron. Explain.
(8%)
6.Write a short esay to explain the basic principles and construction of Scan
tunneling microscopy (STM).
(20%)
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