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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

A

1- 0.732

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
Q

What close packing and coordination is NiAs?

A

HCP 6,6 octahedral Ni, trigonal As

26
Q

Fluorite coordination?

A

CCP = 8,4

all tetrahedral holes filled with F

all octahedral holes empty

27
Q

zinc blende/sphalerite coordination?

A

CCP = 4,4

half tetrahedral holes filled by S-

28
Q

What structure do III-V semiconductors form?

A

zinc blende

29
Q

wurtzite coordination?

A

same as zinc blende but HCP

HCP, 4,4 coordination with half filled tetrahedral holes w/ anions

30
Q

coordination of Li3Bi?

A

FCC with Bi3- in all octahedral, Li+ in all tetrahedral

Li 4 & 6 coordinate
Bi 14 coordinate

31
Q

coordination of CsCl?

A

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
Q

coordination of ReO3

A

simple cubic, 6-coordinate octahedral Re6+, linear 2-coordinate O2-, perovskite structure

33
Q

general formula for spinels

A

AB2X4, A & B = cations, X = anions

34
Q

describe the 2,3 spinel structure

A

Mg2+, Al3+, O2-

FCC oxides, A cations (Mg) in 1/8 tetrahedral holes

B cations in 1/2 octahedral holes

35
Q

How do you work out the no. of octahedral and tet holes in spinels?

A

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
Q

describe the 4-2 spinel structure

A

A4+, B2+, X2-

37
Q

compare inverse spinels to spinels

A

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
Q

for d electrons are s electrons included?

A

YES

39
Q

describe perovskite

A

ABX3, FCC, B cations in oct holes, ReO3 structure with A cation at centre

BO6 octahedra in corners
12 coordinate cuboctahedral A

40
Q

tolerance factor range for hexagonal

A

1<t<1.06

41
Q

tolerance factor range for ideal cubic

A

0.9<t<1

42
Q

tolerance factor range for orthorhombic pervoskite

A

0.8<t<0.9

43
Q

tolerance factor range for other structure types

A

t<0.8

44
Q

what is YBCO

A

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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