Hole filling Flashcards
How many tetrahedral holes are there per sphere in hcp, and where are it/they located?
Two per sphere. One right above and one right below each sphere in the layer.
How many tetrahedral holes per sphere in hcp can be occupied?
One per sphere.
How many tetrahedral holes are there per sphere in ccp, and where are it/they located?
Two per sphere. One right above and one right below each sphere in the layer.
How many tetrahedral holes per sphere in ccp can be occupied?
All.
What kind of closest packing do we have in CaF2, and which holes are occupied?
In CaF2 we have cubic closest packing of Ca with all tetrahedral holes filled by F.
What kind of closest packing do we have in zinc blende, and which holes are occupied?
In zinc blende (e.g. sphalerite, ZnS), we have cubic closest packing of S with half tetrahedral holes filled by Zn.
What kind of closest packing do we have in wurtzite, and which holes are occupied?
In wurtzite (e.g. ZnS) we have hexagonal closest packing of S with half tetrahedral holes filled by Zn.
What is the difference between wurtzite and zinc blende?
Wurtzite is hcp and zinc blende in ccp. Both have ZnS with half tetrahedral holes filled.
What kind of closest packing do we have in rock salt (NaCl) and which holes are occupied?
In rock salt we have cubic closest packing of Na/Cl, with all octahedral holes filled by Cl/Na.
What kind of closest packing do we have in NiAs and which holes are occupied?
In NiAs we have hexagonal closest packing of As with all octahedral holes filled by Ni. Ni stacked on top of each other
What is the coordination polyhedra for As in NiAs-type structure?
Trigonal prism.
What is the coordination polyhedra for Ni in NiAs-type structure?
Octahedron.
What are Heusler alloys?
Heusler alloys are compounds with formula XYZ (Half-Heusler) or X2YZ (Full-Heusler). X and Y are transition metals, Z is p-block.
How can a Heusler alloy be described?
X2YZ (full Heusler), XYZ (half Heusler).
Two fcc-lattices superimposed (shifted [1/2 0 0]) occupied by X. For half Heuslers one of these is unoccupied.
All tetrahedral holes filled by alternating Y and Z.
What are Laves phases?
Compositions MM’2 where M are bigger than M’.
These can be regarded as a superstructure of CsCl. In these cases they have tetrahedra of M’ instead of a single atom. E.g. MgCu2.
How can the partial filling of CA2-compounds be in hcp?
Two types: CdI2 or CaCl2.
CdI2: Every second plane have fully filled octahedral holes.
CaCl2: Every plane has half filled octahedral holes.
How can be the partial filling of CA2-compounds be in ccp?
One type: CdCl2
Every second plane have fully filled octahedral holes.
How can the partial filling of CA3-compounds be in hcp?
Three types: Cr2AlC, RuBr3, BiI3
Cr2AlC: Every third plane fully filled octahedral holes.
RuBr3: Every plane filled 1/3 octahedral holes.
BiI3: Every second plane filled 2/3 octahedral holes.
How can the partial filling of CA3-compounds be in ccp?
One type: YCl3
Every second plane filled 2/3 octahedral holes.
How can the partial filling of C2A3-compounds be in hcp?
One type: Al2O3 (corundum)
Every plane filled 2/3.
How can the partial filling of C2A3-compounds be in ccp?
One type: La2O3
Two planes filled fully octahedral holes, one plane empty.
How is the packing in a spinel?
Spinel: AM2X4
In a spinel there is a combined fractional hole filling of tetrahedral and octahedral intersticies.
There is a cubic closest packing of X (usually oxygen). Two-thirds of metal ions occupy octahedral sites, the rest tetrahedral.
What is an inverse spinel?
Spinel: AM2X4
Normally, larger ions will occupy octahedral sites and smaller ions with occupy tetrahedral sites.
In an inverse spinel, half of the M-ions occupy tetrahedral sites and half octahedral sites, while A occupy octahedral sites.
Degree of inversion is designated by λ (0 < λ < 0.5), where 0.5 indicates inverse spinel and 0 indicates normal.
How can the closest packing in a perovskite be described?
ABX3 - cubic closest packing of AX.
In hcp, how are the octahedral intersticies linked?
- Face-sharing when octahedra are located one on top of the other in the direction c.
- Edge-sharing when they are adjacent in the a-b plane.
- Vertex-sharing when they are adjacent at different heights.
What are the bond angles between bridging atoms of the the octahedral intersticies in hcp for the different arrangements?
- Face-sharing: 70.5°
- Edge-sharing: 90°
- Vertex-sharing: 131.8°
What are the bond angles between bridging atoms of the tetrahedral itnersticies in hcp for the different arrangements?
- Face-sharing: 56.7°
- Edge-sharing: 70.5°
- Vertex-sharing: 109.5°
What are the bond angles between bridging atoms of the the octahedral intersticies in ccp for the different arrangements?
- Face-sharing: There are no face-sharing octahedra in ccp.
- Edge-sharing: 90°
- Vertex-sharing: 180°
What are the bond angles between bridging atoms of the the tetrahedral intersticies in ccp for the different arrangements?
- Face-sharing: There are no face-sharing tetrahedra in ccp.
- Edge-sharing: 70.5°
- Vertex-sharing in octants with common edge: 109.5°
- Vertex-sharing in octants with common vertex: 180°
How are MnP and NiAs related?
MnP is a distorted structure of the NiAs-type. Metal ions are closely linked in the ab-plane in a zigzag-pattern.
