Inorganic materials and nanoparticles Flashcards
What is long range order in terms of crystallinity?
(Page 5)
Crystaline eg. SiO2 as Quartz
What is short range order in terms of crystallinity?
Amorphous eg. SiO2 as glass
What is it called when a solid compound has more than one structure for the same composition?
(Page 6)
Polymorphism
What is a particular polymorph referred to as?
(Page 6)
A phase
Under a set of conditions, how many different polymorphs/phases would you expect to be stable?
(Page 6)
One
Are anions or cations generally larger and which fit into the interstitial sites?
(Page 7)
Anions are larger leading to them being close packed and the cations slotting into the interstitial sites as they’re more mobile
What is the overall charge of a bulk solid?
(Page 7)
Zero, however charge can be distributed heterogenously
What is the temperature at which an ionic crystal will have a perfectly ordered array of atoms?
(Page 8)
0K, above 0K crystals will have defects.
Why do crystals only have defects above 0K?
(Page 8)
Because defect formation requires energy and is always endothermic
If defects are endothermic, what drives their formation?
(Page 8)
Entropy gain, structure becomes more disordered
What happens when ΔH and TΔS lines cross?
(Page 8)
ΔG = 0 meaning the system is at equilibrium, which is where the number of defects for an ionic crystal should be measured
What is a Schottky defect?
(Page 8)
A pair of vacancies in the lattice, two sites are left unoccupied
What is a Frenkel defect? (Page 8)
A defect generated by a cation moving into an interstitial site
When are defects most influential on magnetic, electrical and mechanical properties?
(Page 9)
When they cluster together into regions or planes
Is there a higher proportion of defects in ionic or covalent lattices?
(Page 9)
Covalent, atoms are larger meaning electrostatic interaction is smaller (weaker bonds that are easier to break) hence there are larger proportion of defects
How does temperature affect the proportion of defects?
(Page 9)
Higher temeperature = higher proportion of defects
What is doping?
(Page 9)
Introducing different ions into the structure
How are non-stoichiometric solids formed?
(Page 10)
Defects and doping result in non-stoichiometric solids
How are non-stoichiometric solids distinct from other compositions?
(Page 10)
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)
What is a solid solution? (Page 10)
A crystalline solid that can have continual variable composition for a given structure
What is the equation for E cell, Power and Charge? (Page 13)
E cell = E cathode - E anode
Power (W) = voltage (V) x current (A)
Charge (Ah) = current (A) x time (h) 1 Ah = 3600 C
What is the equation for energy, energy density and specific energy? (Page 13)
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)
For the Gibbs free energy equation what units is the Faraday constant in provided the E cell value is in Volts? (Page 13)
A s (Amp seconds) = Coulombs (C)
What are ferroelectrics? (Page 16)
The response of a dipole to an electrical field, electrical field will displace dipole
What are piezoelectrics? (Page 16)
The response of a dipole to the application of pressure
What are pyroelectrics? (Page 16)
Response of a dipole to heat (photons)
What makes a good dielectric material? (Page 16)
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)
What is the difference in the structures of BaTiO3 at temperatures above and below 120 °C> (Page 17)
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)
What is the equation for an ideal cubic centrosymmetric structure? (Page 18)
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)
