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CHEM313 > Sam - crystal structures > Flashcards

Sam - crystal structures Flashcards

1
Q

Diamond v graphite

A

diamond: electrically insulating (doesn’t conduct), hard

graphite: conducts electricity, soft, lubricant

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2
Q

How do you convert 3D to 2D?

A

look along one of the axes

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3
Q

how are lattice points in a unit cell counted?

A

corner = 1/8
edge = 1/4
face = 1/2
central = 1

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4
Q

what is l-centred?

A

body centred cubic

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5
Q

what is F-centred?

A

face centred cubic

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6
Q

which unit cell parameters are equal for orthorhombic crystals?

A

a, b, c = 3 diff lengths

all angles = 90degrees

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7
Q

which unit cell parameters are equal for tetragonal crystals?

A

a=b, c

all angles = 90

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8
Q

which unit cell parameters are equal for cubic crystals?

A

a = b=c

all angles = 90

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9
Q

difference between face centred and body centred?

A

body = only corners and one in the middle

face = all corners and one on each face too

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10
Q

what packing does face centred do?

A

cubic close packed (CCP) aka (FCC)

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11
Q

Describe CCP

A

ABCA

CN= 12

PE = 0.74/74%

Forms anti-cube octahedron (triangles opposite orientations)

stacking inbetween holes, where there isnt an atom beneath

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12
Q

Describe HCP

A

ABA

CN=12

PE = 0.74/74%

Forms cube octahedron (triangles same orientation)

stacked avoiding the hole between first A &B stack

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13
Q

Describe body centred cubic

A

ABA

CN = 8

PE = 0.68

often metals, not truly close packed

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14
Q

Describe simple cubic

A

CN = 6

PE = 0.52

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15
Q

Describe simple cubic

A

CN = 6

PE = 0.52

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16
Q

Compare properties of HCP/FCC and BCC

A

HCP/FCC: low corrugation of layers, closer packing so layers slip over each other, FCC more ductile, HCP more brittle

BCC: higher corrugation, cubic structure, tends to be harder than FCC but more ductile than HCP

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17
Q

Two types of alloys?

A

substitutional: atoms of one element exchanged for another,

interstitial: additional atoms of another element between atoms of the host lattice

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18
Q

What do A and B usually refer to in ionic solids?

A

A = cation , B=anion

19
Q

What is a eutactic structure?

A

when the structure has expanded to accommodate ions in the interstitial sites (the host ions are no longer touching)

20
Q

radius ratio range for cubic structure

21
Q

radius ratio range for octahedral structure

A

0.732 - 0.414

22
Q

radius ratio range for tetrahedral structure

A

0.414 - 0.225

23
Q

radius ratio range for trigonal structure

A

0.225 - 0.155

24
Q

Examples with rocksalt structure

A

NaCl, MgO, AgCl, KBr, CaO, transition metal monoxides

25
What close packing and coordination is NiAs?
HCP 6,6 octahedral Ni, trigonal As
26
Fluorite coordination?
CCP = 8,4 all tetrahedral holes filled with F all octahedral holes empty
27
zinc blende/sphalerite coordination?
CCP = 4,4 half tetrahedral holes filled by S-
28
What structure do III-V semiconductors form?
zinc blende
29
wurtzite coordination?
same as zinc blende but HCP HCP, 4,4 coordination with half filled tetrahedral holes w/ anions
30
coordination of Li3Bi?
FCC with Bi3- in all octahedral, Li+ in all tetrahedral Li 4 & 6 coordinate Bi 14 coordinate
31
coordination of CsCl?
simple cubic array of Cl-, 8,8, cubic hole occupied with Cs, no close packing NOT body centred cubic as there is no central Cl- as the central lattice point
32
coordination of ReO3
simple cubic, 6-coordinate octahedral Re6+, linear 2-coordinate O2-, perovskite structure
33
general formula for spinels
AB2X4, A & B = cations, X = anions
34
describe the 2,3 spinel structure
Mg2+, Al3+, O2- FCC oxides, A cations (Mg) in 1/8 tetrahedral holes B cations in 1/2 octahedral holes
35
How do you work out the no. of octahedral and tet holes in spinels?
8 formula units per unit cell, no. of oxygens x 8 = oct holes tet holes = no. of oct x 2 use ratio of A cation to the oxygens (e.g. MgO4 Mg = 1/4) x no. of oxygens to get the no. in the tet holes (then divide this no. by the no. of tet holes) do the same for B in the oct holes
36
describe the 4-2 spinel structure
A4+, B2+, X2-
37
compare inverse spinels to spinels
spinels: A cations in 1/8 tet holes, B cations in 1/2 oct holes inverse spinels: A cations in 50% of 1/2 oct holes, B cations in tet and the other 50% of 1/2 oct
38
for d electrons are s electrons included?
YES
39
describe perovskite
ABX3, FCC, B cations in oct holes, ReO3 structure with A cation at centre BO6 octahedra in corners 12 coordinate cuboctahedral A
40
tolerance factor range for hexagonal
1
41
tolerance factor range for ideal cubic
0.9
42
tolerance factor range for orthorhombic pervoskite
0.8
43
tolerance factor range for other structure types
t<0.8
44
what is YBCO
1,2,3 superconductor YBa2Cu3O7 high temp superconductor - oxide loss makes it a semi-conductor rather than superconductor

CHEM313 (6 decks)

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