Complex crystal structures Flashcards
(22 cards)
What is a Perovskite structure?
ABX3 - ccp of larger ions and small cations fill 1/4 of oct sites
What are the two kinds of Perovskite structures?
B type and A type
What is a B type Perovskite structure?
Primative: A on corners, B in the center and X in the faces
What is an A type Perovskite structure?
Primative: A in the center, B in the corners and X in the edges
When is Perovskite most common?
Oxygen and fluorine anions
What is the polyhedra of Perovskite?
Vertex linked octahedra
What structures do AX3 compounds form?
Non-close packed with A on corners and X on the edges
What is the polyhedra of AX3 compounds?
Vertex linked octahedra
What are Tungsten bases?
An intermediate between Perovskites and AX3. Can have varying Na atoms. High Na = metallic, low Na = semiconducting
How are AX structures formed?
Filling all of the octahedral holes or half of the tetrahedral holes
Describe NaCl
CCP with all octahedral holes filled, both have octahedral environments with coordination no of 6
Where do the atoms occupy in NaCl
Na in holes as anions are bigger
Describe NiAs
HCP with all octahedral holes filled
Where do the atoms occupy in NiAs
Ni in the holes
Describe Zinc Blende
CCP with half tetrahedral holes filled, both have tetrahedral environments with coordination no of 4
Where do the atoms occupy in Zinc Blende
Zn in the holes
Describe Wurtzite
HCP with half tetrahedral holes filled, both have tetrahedral environments with coordination no of 4
What are some examples of AX structures?
NaCl, NiAs, ZnS (zinc blende), ZnS (Wurtzite), CsCl
What are some examples of AX2 structures?
CaF2, CdI2, CdCl2, TiO2
Describe CaF2
FCC, anions in tetrahedral holes, edge sharing polyhedra
Describe Na2O
Anti-fluorite structure, FCC, cations in tetrahedral holes, edge sharing polyhedra
Describe CdCl2
FCC, cations fill half of octahedral holes with middle ones missing. Similar to NaCl
