2008 Material Science

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2a)calculate the number of vacancies per cubic meter in gold 900C given that the energy of vacancy

formation is 0.98 eV per atom and density and atomic weight of gold 900C are 18.63 grams per and196.9 grams per mole respectively.

This involves evaluating the equation

Nv =N

We need to find N using the equation

N=

=()

=5.598*

Nv = 5.598*

= 3.458*

Sketch and describe briefly twinning and twin boundary in crystal

When two atom are separated by a boundary and one of the atom on one side is a mirror image other the atoms is a

twin and the boundary separating both atoms is the twin boundary. See diagram below

Twin

Twin boundary

2c) what are super and partial dislocation? Explain in detail Frank and Shockley dislocations and their effect on

stacking faults.

The whole: 2 dislocations plus anti phase boundary is called a super dislocation. The 2 dislocations repel each other,

and move from each other. A so-called anti-phase boundary will occur.

A partial dislocation in which the Burger's vector lies in the fault plane, so that it is able to glide, in contrast to a

Frank partial dislocation


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What is ferroelectricity? Sketch the unit cell of BaTi and explain why ferroelectricity is observed in this ceramicmaterial.

Ferroelectricity is a property of certain materials which possess a spontaneous electric polarization that can be

reversed by the application of an external electric field

Depending upon their behavior in an external magnetic field,superconductors are divided into two types:

a) Type I superconductors and b) Type II superconductors

Let us discuss them one by one:

1) Type I superconductors:

a). Type I superconductors are those superconductors which loose their superconductivity very easily or abruptly

when placed in the external magnetic field. As you can see from the graph of intensity of magnetization (M) versus

applied magnetic field (H), when the Type I superconductor is placed in the magnetic field, it suddenly or easily

looses its superconductivity at critical magnetic field (Hc) (point A).
http://en.wikipedia.org/wiki/Polarization_densityhttp://www.winnerscience.com/superconductivity/superconductors-critical-temperature-critical-magnetic-field-and-meissner-effect/http://www.winnerscience.com/superconductivity/superconductors-critical-temperature-critical-magnetic-field-and-meissner-effect/http://en.wikipedia.org/wiki/Polarization_density


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After Hc, the Type I superconductor will become

conductor.

b). Type I superconductors are also known as soft superconductors because of this reason that is they loose their

superconductivity easily.

c) Type I superconductors perfectly obey Meissner effect.

d) Example of Type I superconductors: Aluminum (Hc = 0.0105 Tesla), Zinc (Hc = 0.0054)

2) Type II superconductors:

a). Type II superconductors are those superconductors which loose their superconductivity gradually but not easily

or abruptly when placed in the external magnetic field. As you can see from the graph of intensity of magnetization

(M) versus applied magnetic field (H), when the Type II superconductor is placed in the magnetic field, it gradually

looses its superconductivity. Type II superconductors start to loose their superconductivity at lower critical magnetic

field (Hc1) and completely loose their superconductivity at upper critical magnetic field (Hc2).

b) The state between the lower critical magnetic field (Hc1) and upper critical magnetic field (Hc2) is known as

vortex state or intermediate state.

After Hc2, the Type II superconductor will become conductor.

c). Type I superconductors are also known as hard superconductors because of this reason that is they loose their

superconductivity gradually but not easily.

c) Type I superconductors obey Meissner effect but not completely.

d) Example of Type I superconductors: NbN (Hc = 8 x 106

Tesla), Babi3 (Hc = 59 x 103

Tesla)

e) Application of Type II superconductors: Type II superconductors are used for strong field superconducting

magnets.
http://www.winnerscience.com/superconductivity/superconductors-critical-temperature-critical-magnetic-field-and-meissner-effect/http://www.winnerscience.com/superconductivity/superconductors-critical-temperature-critical-magnetic-field-and-meissner-effect/http://www.winnerscience.com/superconductivity/type-i-and-type-ii-superconductors/attachment/fig-type-ii/http://www.winnerscience.com/superconductivity/type-i-and-type-ii-superconductors/attachment/fig-type-1/http://www.winnerscience.com/superconductivity/type-i-and-type-ii-superconductors/attachment/fig-type-ii/http://www.winnerscience.com/superconductivity/type-i-and-type-ii-superconductors/attachment/fig-type-1/http://www.winnerscience.com/superconductivity/superconductors-critical-temperature-critical-magnetic-field-and-meissner-effect/http://www.winnerscience.com/superconductivity/superconductors-critical-temperature-critical-magnetic-field-and-meissner-effect/

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2008 Material Science