Solid state chemistry

What is the role of the catalyst?

reduce the over-potential for the reaction and to modulate selectivity

overpotential

potential difference/ energy needed beyond what is thermodynamically expected to drive a reaction

CO₂ Electrolyser structure

hexagonal close packed crystal structure

ABABA…. layering

cubic close packed crystal structure

ABCABC…. layering

What are the two types of interstitial sites?

tetrahedral— in direct proximity to 4 atoms

octahedral— in direct proximity to 6 atoms

What is the the three types of packing that can result from the filling of the interstitial sites

What are some common defects found in solids?

vacant sites

misplaced atoms

TRUE OR FALSE: Defect free crystals don’t exist

TRUE; can only be theoretically observed at absolute zero

a) Stoichiometric and b) non-stoichiometric defects

a) crystal composition is unchanged due to the defect

b) results in a change in the composition of the crystal.

What types of defects are a) Frenkel and b) Schottky?

a) atom has been displaced onto an interstitial site; stoichiometric

b) site vacancies present overall charge balance is maintained; stoichiometric

What structural features makes Frenkel defects more likely?

low co-ordination open structures

significant difference in size between the cation and the anion

What are the types of non-stoichiometric defects?

an atom is added within the crystal lattice, either filling interstitial site or substitute for atoms

What are the guidelines for the atom causing substitutional defects?

must have same charge and similar size (±15%) to replaced atom

Extended defects: what are they and what are some types?

affect order of many unit cells

Stacking fault: ‘mix-up’ in the packing arrangement of layers (eg. ABA→ABC)

Edge Dislocations (pictured): an extra half plane of atoms exist that go part way through the structure

Wat effect does applying stress to a metal have?

hardens it; the number of grain boundaries and dislocations are increased creating boundaries at which the slip plane is stopped (slip planes can shift laterally)

Metals with what types of unit cells are most malleable and why?

fcc unit cells because slips