Intro to solid state chemistry Flashcards
Crystalline solid
a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions
Amorphous solid
a solid that lacks long-range order and doesn’t organise into a definite lattice pattern
2D lattice counting: atoms in centre of cell
1
2D lattice counting: atoms on edge of cell
1/2
2D lattice counting: atoms at a corner of cell
1/4
3D lattice counting: atoms in centre of cell
1
3D lattice counting: atoms on edge of cell
1/4
3D lattice counting: atoms at a corner of cell
1/8
3D lattice counting: atoms on face of cell
1/2
Packing efficiency formula
Natoms*Vatom / Vunit cell
Laves Principles
regarding the packing of spheres
- space
- symmetry
- connection
Two types of close packing
- Hexagonal close packing (hcp); ABABAB…
- Cubic close packing (ccp); ABCABC…
Coordination no. of close packing
12
Packing efficiency of close packing
74%
Primitive cubic packing
(sites of atoms, packing efficiency, coordination number, points of contact)
- M at (0,0,0)
- 52% of volume occupied
- coordination no. = 6
- spheres in contact along cell edges
Body centred cubic packing
(sites of atoms, packing efficiency, coordination number, points of contact)
- M at (0,0,0) and (1/2, 1/2, 1/2)
- 68% of volume occupied
- coordination no. = 8
- spheres in contact along body diagonal
CsCl structure
Cl at (0,0,0)
Cs at (1/2, 1/2, 1/2)
two interpenetrating primitive cubic lattices
Are Oh or Td holes bigger
Oh
If there are n spheres, how many Oh holes are there?
n
If there are n spheres, how many Td holes are there?
2n
NaCl structure
- Na in all Oh holes of a CCP of Cl
- 6:6 coordination
- 2 interpenetrating CCP arrays
Rutile
TiO 2
- distorted HCP of O with Ti in half Oh holes
- edge and corner sharing TiO 6 octahedra
Fluorite
CaF 2
- all tetrahedral holes in CCP
- Ca is surrounded by 8 F
- F is surrounded by 4 Ca
- 8:4 coordination
NiAs
- all octahedral holes in HCP
- HCP of As with Ni in Oh holes
- As in trigonal prism of Ni
- 6:6 coordination
- Ni octahedra share faces
Perovskite
ABO 3
- ideal cubic structure
- Ti octahedrally coordinated
- Ca is 12 coordinated
- Ti in Oh holes
- corner sharing BO 6 octahedra
What are the allowed oxidation states in perovskite
3+ / 3+
2+ / 4+
1+ / 5+
Ferroelectric Material
dielectric materials in which polarisation remains permanently, even after removing the applied electric field
Crystal polymorphism
compound can crystallise into more than one crystal structure
Spinel
AB 2 O 4
- Mg in MgO 4 tetrahedra
- Al in AlO 6 octahedra
- close packed O layers
- A and B are in some of the Td and Oh holes
Allowed Oxidation states of spinels
2+ / 3+
1+ / 4+
Most favourable conditions for radius ratio rules
- ions treated as hard spheres
- cation-anion contact
- no anion-anion contact
- coordination no. is max possible
Lattice energy
the change in internal energy when 1 mole of an ionic compound at 1 bar is formed from infinitely separated gaseous ions
What is the madelung constant?
the sum of the partial madelung constants which represent the contributions of the individual ions to the total lattice energy
How does Born-Lande Equation differ from Born-Mayer?
Born-Mayer uses density as measuring the repulsion term
How does Born-Lande Equation differ from Kapustinkii?
Kapustinkii can be used to estimate lattice energy without the knowledge of the structure type (i.e. the madelung constant)
How types of polycrystalline materials are formed
- conventional solid state reactions
- precursor methods
- hydrothermal / solvothermal methods
- intercalation ion exchange
How types of single crystals are formed
- single crystal growth from melt
- single crystal growth from fluxes
- floating zone furnace (large) crystal growth
How thin films are formed
- chemical vapour deposition
- sputtering
Why is grinding needed in ‘shake and bake’?
- produces an intimate mixture of reactants
- reduces reactant particle size
Why are high temperatures required for ‘shake and bake’?
- generally leads to thermodynamically stable products
What method is used to deduce crystal structures?
x-ray diffraction
Solid oxide fuel cells: positives and negatives
+ve = clean and efficient energy generation, fuel flexibility, zero CO 2 emissions
-ve = device cost and reliability
Solid oxide fuel cells: electrolyte used
YSZ
Yttria-stabilised zirconia
Isovalent Substitution
the ion that is substituting the original ion is of the same oxidation state as the ion replacing it
Aliovalent Substitution
the ion that is substituting the original ion is of a different oxidation state than the ion it is replacing
Two mechanisms for ionic conduction
- Vacancy-hopping oxide ion conductors
- Interstitial oxide ion conductors
Example of other ionic conductor
Layered materials containing mobile cations
used in rechargeable battery materials
Superconductors
a type of material that conducts electricity with zero energy loss or resistance when cooled to a certain temperature
Example of molecular superconductors
Alkali fullerides, A 3 C 60
Factors for elements replacing one another in doping
- Oxidation state (similar oxidation state is favourable)
- Ionic radii (similar sizes is favourable)
- Coordination preferences (geometry)
