b) List the assumptions of the independent electXon model. Explain the need for. these assumptions. c) Describe the dist
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PG – 121
*PG121*
III Semester M.Sc. Degree Examination, December 2014 (2010 – 11 Scheme) (N.S.) CHEMISTRY C-301 – IC : Solid State Chemistry Time : 3 Hours
Max. Marks : 80
Instruction : Answer question No. 1 and any five of the remaining. 1. Answer any ten of the following :
(2×10=20)
a) In the free electron theory, why is the potential of the electron outside the ‘box’ assumed to be infinity ? b) What are phonons ? How are they responsible for the Ohmic resistance of metals ? c) What is responsible for the ‘metal like conduction’ in graphite ? d) How does band theory explain the metallic nature of Mg ? e) Why does NiO. behave as an insulator ? f) What is inverse piezoelectric effect ? g) What are the parameters correlated in a dispersion relation ? h) Why are Frenkel defects uncommon in the anion sublattice ? i) What are Cooper Pairs ? °
°
°
j) A crystal has a = 3.01 A , b = 5.02 A , c = 8.7 A , α = γ = 90° and β = 102°. Identify the crystal system. k) What does the following space group notation imply I1
2 1? c
l) What are allowed point groups in the triclinic crystal system ? 2. a) What are the limitations of free electron theory ? b) List the assumptions of the independent electXon model. Explain the need for these assumptions. c) Describe the distortions of a cubic BaTiO3 crystal at the different transition temperatures. (3+4+5) P.T.O.
*PG121*
PG – 121 3. a) What is Peltier effect ? b) Explain the origin of weak paramagnetism in a free electron metal.
c) With suitable geometric constructions obtain the relationship between hkl (3+4+5) and dhkl for a cubic crystal. 4. a) Differentiate between intrinsic and extrinsic semiconductors. b) Discuss the types of line defects in crystals. c) How is the order of a phase transition defined within Ehrenfests thermodynamic classification of phase transitions ? (4+4+4) 5. a) Write the Wierl equation and explain all the terms. b) Plot schematically the variation in the intensity of magnetization versus the applied magnetic field for Type I and Type II superconductors. c) Discuss the salient features of the theory of low temperature superconductivity. (3+4+5) 6. a) Write the expression for the structure factor and explain all the terms involved. b) Describe the nature of order disorder transitions with a suitable example. c) Write on the origin and construction of reciprocal lattice based on Bragg’s law. (3+5+4) 7. a) What is the phase problem in X-ray diffraction ? b) Discuss the role of Patterson synthesis in X-ray structure determination. c) Describe briefly the working of a Weissenberg Camera. How is it superior to a rotation – oscillation camera ? (3+4+5)
