Inorganic materials and nanoparticles

Question 1

What is long range order in terms of crystallinity?
(Page 5)

Answer 1

Crystaline eg. SiO2 as Quartz

Question 2

What is short range order in terms of crystallinity?

Answer 2

Amorphous eg. SiO2 as glass

Question 3

What is it called when a solid compound has more than one structure for the same composition?
(Page 6)

Answer 3

Polymorphism

Question 4

What is a particular polymorph referred to as?
(Page 6)

Answer 4

A phase

Question 5

Under a set of conditions, how many different polymorphs/phases would you expect to be stable?
(Page 6)

Answer 5

One

Question 6

Are anions or cations generally larger and which fit into the interstitial sites?
(Page 7)

Answer 6

Anions are larger leading to them being close packed and the cations slotting into the interstitial sites as they’re more mobile

Question 7

What is the overall charge of a bulk solid?
(Page 7)

Answer 7

Zero, however charge can be distributed heterogenously

Question 8

What is the temperature at which an ionic crystal will have a perfectly ordered array of atoms?
(Page 8)

Answer 8

0K, above 0K crystals will have defects.

Question 9

Why do crystals only have defects above 0K?
(Page 8)

Answer 9

Because defect formation requires energy and is always endothermic

Question 10

If defects are endothermic, what drives their formation?
(Page 8)

Answer 10

Entropy gain, structure becomes more disordered

Question 11

What happens when ΔH and TΔS lines cross?
(Page 8)

Answer 11

ΔG = 0 meaning the system is at equilibrium, which is where the number of defects for an ionic crystal should be measured

Question 12

What is a Schottky defect?
(Page 8)

Answer 12

A pair of vacancies in the lattice, two sites are left unoccupied

Question 13

What is a Frenkel defect? (Page 8)

Answer 13

A defect generated by a cation moving into an interstitial site

Question 14

When are defects most influential on magnetic, electrical and mechanical properties?
(Page 9)

Answer 14

When they cluster together into regions or planes

Question 15

Is there a higher proportion of defects in ionic or covalent lattices?
(Page 9)

Answer 15

Covalent, atoms are larger meaning electrostatic interaction is smaller (weaker bonds that are easier to break) hence there are larger proportion of defects

Question 16

How does temperature affect the proportion of defects?
(Page 9)

Answer 16

Higher temeperature = higher proportion of defects

Question 17

What is doping?
(Page 9)

Answer 17

Introducing different ions into the structure

Question 18

How are non-stoichiometric solids formed?
(Page 10)

Answer 18

Defects and doping result in non-stoichiometric solids

Question 19

How are non-stoichiometric solids distinct from other compositions?
(Page 10)

Answer 19

They have the same structure within a range of x. For example TiOx, within the range 0.7 < x < 1.25, all compounds (no matter the value of x have same structure, although volume will vary) (TiO would have same structure as TiO1.25)

Question 20

What is a solid solution? (Page 10)

Answer 20

A crystalline solid that can have continual variable composition for a given structure

Question 21

What is the equation for E cell, Power and Charge? (Page 13)

Answer 21

E cell = E cathode - E anode
Power (W) = voltage (V) x current (A)
Charge (Ah) = current (A) x time (h) 1 Ah = 3600 C

Question 22

What is the equation for energy, energy density and specific energy? (Page 13)

Answer 22

Energy (Wh) = power (W) x time (h)
Energy density = Energy stored per volume (Wh L^-1)
Specific energy = Energy stored per mass (Wh kg^-1)

Question 23

For the Gibbs free energy equation what units is the Faraday constant in provided the E cell value is in Volts? (Page 13)

Answer 23

A s (Amp seconds) = Coulombs (C)

Question 24

What are ferroelectrics? (Page 16)

Answer 24

The response of a dipole to an electrical field, electrical field will displace dipole

Question 25

What are piezoelectrics? (Page 16)

Answer 25

The response of a dipole to the application of pressure

Question 26

What are pyroelectrics? (Page 16)

Answer 26

Response of a dipole to heat (photons)

Question 27

What makes a good dielectric material? (Page 16)

Answer 27

A material that has a high dielectric strength (meaning it doesn’t break down at high voltages and become electron conducting), and have a low dielectric loss (doesn’t lose electrical energy as heat energy)

Question 28

What is the difference in the structures of BaTiO3 at temperatures above and below 120 °C> (Page 17)

Answer 28

Above 120 °C the titanium atoms are in a symmetric octahedral TiO6 site (gives cubic BuTiO3 centrosymmetric)

Below 120 °C the Ti atoms are displaced along one of the TiO6 axes (gives tetragonal BuTiO3 non-centrosymmetric)

Question 29

What is the equation for an ideal cubic centrosymmetric structure? (Page 18)

Answer 29

t x 2(rB + rO) = √2 (rA + rO) where t = 1
As t deviates from 1, structure is distorted because 2(rB + rO) = √2 (rA + rO) is no longer true (it’s true for a cube so we know structure has distorted from cubic centrosymmetric)