III Semester M.Sc. Degree Examination, December 2013/January 2014 (2010-2011 Scheme) (NS) CHEMISTRY C-301-PC : Chemistry of Solids and Diffraction Methods Time : 3 Hours
Max. Marks : 80
Instruction : Answer question 1 and any five of the remaining. 1. Answer any ten of the following :
(2×10=20)
a) What is a Fermi level ? Mention its importance.
b) Give the relationship of k with the momentum p of a free electron and write its units.
c) Define screw axis. Depict the generation of equivalent points for 3, screw axis. d) To which category the following transformations belong : (i) Graphite → Diamond (ii) Quartz → Cristobalite. e) What is the difference between ferroelectric and paraelectric material. f) Define (i) Phonon (ii) Friedel pa.r. g) Name the element that you would dope into Si lattice to get a (i) n-type and (ii) p-type semiconductor. h) What is an interstitial defect ? i) Calculate the d236 spacing for a cubic crystal with cell length of 3×10 –10 m. j) What does f j, the scattering factor signify ? k) List the Hermann-Mauguin notations for symmetry elements of a crystal lattice. l) Write Wierl equation and explain the terms involved. 2. a) Explain the conductivity of a free electron in a solid by deriving the Ohm’s Law equation.
b) Give the significance of the value of wave vector k in a crystalline solid.
(6+6=12) P.T.O.
PG – 352
-2-
*PG352*
3. a) Obtain on expression for the density of states. b) Draw Froblich diagram. Explain how a Cooper pair of electrons undergo scattering without loss of momentum. (6+6=12) 4. a) From thermodynamic values, how are phase transformations in solids classified ? b) What is Schottky defect ? Obtain an equation relating the number of atoms and the number of Schottky defects. (6+6=12) 5. a) How do you differentiate between Type – I and Type – II superconductors ? b) Explain Weissenberg method and its applications. c) How is neutron scattering different from X-ray scattering ?
(4+4+4=12)
6. a) Diagrammatically depict P, I, F and C lattice types. What does each symbol signify ? How many lattice sites are there in each ? b) Write Euler’s equation and explain its importance. Find out whether 432 and 642 combination of rotation axes are allowed or not in solids. c) 5-fold and >6-fold does not exists in crystal lattice. Explain.
(3+5+4=12)
7. a) Draw the band structure of a p-n junction and explain its function. b) List the four components of the polarizability term for a dielectric material and explain their contribution. c) Describe the Radial-Distribution method for the determination of bond lengths and bond angles in a gaseous molecule. (4+4+4=12)
c) How is neutron scattering different from X-ray scattering ? (4+4+4=12). 6. a) Diagrammatically depict P, I, F and C lattice types. What does each symbol.
g) Isotopes can be differentiated accurately from neutron diffraction. Explain. h) What is phase problem ? i) How does Fermi energy vary with temperature for an ...
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