PG – 350

*PG350*

III Semester M.Sc. Degree Examination, December 2013/January 2014 (2010-11 Scheme) (NS) CHEMISTRY C-301-IC : Solid State Chemistry Time : 3 Hours

Max. Marks : 80

Instruction : Answer question No. 1 and any five of the remaining questions. 1. Answer any ten of the following :

(10×2=20)

a) Differentiate between p-type and n-type semiconductors. b) State the law of interfacial angles. c) What is piezoelectric effect ? d) Write dhkl as a function of Miller indices and lattice parameter of cubic crystal and tetragonal crystal. e) The vibration spectrum of a solid reveals two modes of vibration : i) 150 cm–1 which varies linearly with q , the reciprocal lattice vector and


ii) 1500 cm–1, which is independent of q . Which of these is an optical mode ? Give reasons.


f) What is the effect of temperature on the conductivity in semiconductor ? g) Define “Ewald’s sphere of reflection”. h) Using the Frolisch diagram show how a cooper pair of electrons can undergo scattering without loss of momentum. i) Highlight the advantages of neutron diffraction over X-ray diffraction. j) What are grain boundaries ? k) Differentiate between mirror plane and glide plane. l) Which phase transition is termed as Lamda transition and why ? P.T.O.

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2. a) What is the phase problem in X-ray diffraction ? Describe the Patterson synthesis approach to overcome the phase problem. b) Specify lattice type, crystal system and the principal symmetry elements in the following space groups i) P2221 ii) I4/m iii) Fm3m.

(6+6=12)

3. a) Using relevant equations show that electron density function is Fourier transform of the structure factor. b) The density of the orthorhombic compound (a = 4 A , b = 5 A , c = 6 A ) is 5.79/cc. If the unit cell contains four molecules, calculate the molecular weight of the compound.








c) Define scattering factor. How does it vary with Bragg angle θ ?

(4+4+4=12)

4. a) How do you differentiate between Type I and Type II superconductors ? b) List the various factors responsible for origin of resistivity of metals. c) Explain the Debye-Scherrer powder method.

(4+4+4=12)

5. a) Explain the conductivity of a free electron in a solid by deriving the ohm law equation. b) Write the Schrodinger equation for an electron in a weak periodic potential write any one form of its solution and explain all the terms. c) Make a schematic plot of the variation in resistivity, ρ with temperature, T i) expected for a normal metal and ii) observed in the care of a super conductor.

(5+4+3=12)

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6. a) Prove that 5 fold rotation axis does not exist in crystal lattice. b) Write a note on reciprocal lattice concept. c) Write the characteristic features of Martensitic transition.

(4+4+4=12)

7. a) Derive an expression for the energy of the Fermilevel of a n-type extrinsic semiconductor. How does the Ef vary with T the temperatures ? b) Make a schematic plot of In σ versus

1 T

for an extrinsic semiconductor and

indicate the different regions. c) Describe the Peltier effect.

(6+3+3=12)

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