Zero-dimensional or point defects - Classification and Structure of Materials - Engineering Sciences Previous Year Questions

1

2007 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2007

The enthalpy of formation of vacancies in Cu is 120 kJ.mol^-1. The equilibrium fraction of vacant lattice sites in Cu at 1000 K would be

A

1.35 x 10^-8

B

5.39 x 10^-7

C

7.76 x 10^-6

D

2.58 x 10^-9

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2

2007 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2007

Cd²⁺ doped NaCl crystal has higher conductivity at room temperature as compared to pure NaCl due to

A

lower activation energy for movement of cations

B

increase in the concentration of cation vacancies

C

introduction of holes in the crystal

D

increase in concentration of anion vacancies

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3

2008 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2008

A Schottky defect in CaF₂ is comprised of

A

one Ca²⁺ vacancy and one F⁻ vacancy

B

one Ca²⁺ vacancy and one F⁻ interstitial

C

two Ca²⁺ vacancies and one F⁻ vacancy

D

one Ca²⁺ vacancy and two F⁻ vacancies

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4

2010 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2010

A Frenkel defect is

A

A pair of cation and anion vacancy

B

A pair of cation interstitial and cation vacancy

C

A cation vacancy

D

An anion vacancy

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5

2012 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2012

A Schottky defect in an ionic crystal is a stoichiometric defect of

A

Cation vacancy

B

Anion vacancy

C

Cation and anion vacancy

D

Cation and anion interstitial

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6

2014 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2014

The equilibrium concentration of vacancies in a pure metal

A

increases exponentially with temperature

B

decreases exponentially with temperature

C

varies linearly with temperature

D

is independent of temperature

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7

2015 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2015

Vacancies play an important role in

A

deformation twinning

B

self diffusion

C

strain hardening

D

cross-slip

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8

2017 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2017

Which of the following is a Frenkel defect?

A

One Cl vacancy and one Na vacancy in NaCl

B

One Zn vacancy and one Zn interstitial in ZnO

C

K at the Na site in NaCl

D

None of the above

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9

2017 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2017

If the energy of formation of vacancies in pure copper is 0.9 eV, the fraction of vacancies in pure copper at 27 °C will be ………..×10^-16 (Boltzmann’s constant is 8.62×10^-5 eV/K)

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10

2019 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2019

In NaCl, the substitution of a Na⁺ ion by a Ca²⁺ ion would most probably lead to

A

the formation of a Na⁺ vacancy

B

the creation of a Cl⁻ interstitial

C

the formation of a Cl⁻ vacancy

D

the formation of a Na⁺ and Cl⁻ vacancy pair

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11

2020 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2020

The number of Schottky defects per mole of KCl at 300 °C under equilibrium condition will be:
Given:
Activation energy for the formation of Schottky defect = 250 kJ.mol^-1
Avogadro number = 6.023 × 10²³ mol^-1
Universal Gas Constant = 8.314 J.K^-1.mol^-1

A

1.21 × 10¹⁸

B

1.52 × 10¹⁶

C

9.75

D

2.42 × 10¹²

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12

2023 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2023

Aliovalent doping of $MgCl_2$ in $NaCl$ leads to the formation of defects. Which one of the following is the correct defect reaction?

A

$Mg_{Cl}^{\bullet} + Na_{Na} + V_{Cl}^{'} = \emptyset$

B

$Mg_{Na}^{\bullet} + Cl_{Cl} + V_{Na}^{'} = \emptyset$

C

$Mg_{Na} + Cl_{Cl} = \emptyset$

D

$Mg_{Na}^{\bullet} + Cl_{Cl} + V_{Na}^{\bullet} = \emptyset$

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13

2024 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2024

Which of the following figures schematically represent(s) either the Frenkel defect or the Schottky defect in ionic solids?

A

Figure (A): A 3x4 grid of alternating blue and orange circles with one orange circle missing from the middle row.

B

Figure (B): A 3x4 grid of alternating blue and orange circles with one orange circle displaced to an interstitial position in the middle row.

C

Figure (C): A 3x4 grid of alternating blue and orange circles with two orange circles missing from the middle row.

D

Figure (D): A 3x4 grid of alternating blue and orange circles with one orange circle missing from the middle row and another orange circle displaced to an interstitial position.

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14

2026 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2026

The equilibrium vacancy concentration in aluminum at 900 K is \(1.1 \times 10^{-4}\). The enthalpy of formation of vacancies, in kJ.mol\(^{-1}\), is __________ (rounded off to one decimal place).
Given: Universal gas constant = \(8.314 \text{ J.K}^{-1}.\text{mol}^{-1}\)

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15

2026 · Engineering Sciences · Classification and Structure of Materials · Zero-dimensional or point defects

Engineering Sciences (XE) 2026

Which one of the following statements regarding point defects in ionic solids is correct?

A

Frenkel defects are dominant in those ionic solids where there is a considerable size difference between the cation and anion.

B

Schottky defects are dominant in those ionic solids where there is a considerable size difference between the cation and anion.

C

Schottky defects are the dominant defects in all ionic solids.

D

Similar density of both Frenkel and Schottky defects is present in all ionic solids.

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