SC Flashcards
define crystal
a regular, periodic arrangement of atoms, ions or molecules
define motif
a periodic pattern that becomes associated with each point in the lattice
deffine lattice
defines the periodicity of the structure
define crystal structure
regular pattern defined by the lattice and the motif
define unit cell
a repeating unit that can generate the entire structure by translation in 3 dimensions
what does an atom in the corner of a unit cell contribute
1/8
what does an atom in the edge of a unit cell contribute
1/4
what does an atom in the face of a unit cell contribute
1/2
what does an atom fully within a unit cell contribute
1
what are miller indices used for
to label planes across a unit cell
what are the 2 true close packed systems
hexagonal and cubic close pack
what is the packing efficiency of a truly close packed structure
0.74
what is the formula for packing efficiency
n atoms in UC x V atom / V (UC)
what is the coordination number of a truely close packed system
12
what pattern does cubic close pack follow
ABC
what pattern does hexagonal close pack follow
AB
why is body centred cubic packing not truly close pack
only has PE of 0.68 and a coordination number of 8
what is the PE and CN of simple cubic packing
PE - 0.52
CN - 6
what effect does corrugation have on hexagonal close packed structures
low corrugation
more brittle
what effect does corrugation have on cubic close packed structures
low corrugation
more ductile
how does the corrugation of body centred cubic differ to hexagonal and cubic close pack
higher corrugation
harder than CCP
more ductile than HCP
what is an alloy
a metallic containing atoms of 2 or more metals
what are the 3 types of alloy
pure metal
substitutional alloy
interstitial alloy
how does an alloy change properties
disrupts periodicity