disorted lattice

Question 1

What is a Direct Interstitial Jump

Answer 1

movement of atoms from one interstitial site to
another neighboring interstitial site without permanent displacement any of
the atoms in the matrix crystal lattice

Question 2

when does a Direct interstitial mechanism happen?

Answer 2

occurs when an atom is of small radius. Smaller atoms cause less distortion of the lattice during migration and diffuse more readily than ones having larger atomic radii; being small allows them to fit into interstitial sites and to jump from one interstitial site to another without greatly displacing the solvent atoms from their normal lattice sites

Question 3

Interstitialcy Mechanism

Answer 3

lattice member from one interstitial position to another

Question 4

when are crystal defects important?

Answer 4

– solid oxide fuel cells

Question 5

name of the two defects

Answer 5

Schottky and Frenkel defects

Question 6

Schottky Defect

Answer 6

this type of point defect forms when oppositely charged ions leave their corresponding lattice sites, creating a pair of vacancy defects.

Question 7

frenkel defect

Answer 7

smaller ion leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location.

Question 8

ion migration schottky

Answer 8

To get across the unit cell into the vacancy in this NaCl crystal,
the Na+ ion must hop through the center of the cube where it squeezes past 4 Cl- and 2 Na+. The energy of this “transition state” will determine the ease of migration.

Question 9

what is the formula for the schottky defect?

Answer 9

anion + cation —– V anion + V cation

Question 10

what is the formula for the frenkel defect?

Answer 10

ion — V ion + ion intersititual

Question 11

in Schottky and frenkel defects the charge is….

Answer 11

neutral.

Question 12

direct intersitiual jump powerpoint definition

Answer 12

The ion sits on top of the layer / intersitually and it moves to the vacant site from one unit cell to another

Question 13

indirect intersitual jump

Answer 13

forces an ion out of their vacancy

Question 14

Schottky does

Answer 14

ion migration.

Question 15

what is ion migration?

Answer 15

ion moves across unit cell into the vacant site.

Question 16

defects are present in all…

Answer 16

crystals

Question 17

why are defects present in all crystals

Answer 17

as there is an equilbrium for defects

Question 18

what is the formula for defects

Answer 18

n - Nexp(-Ev.Kbt)

Question 19

asides from heat what other techniques are used to create defects

Answer 19

X-rays
Radioactive decay

Question 20

X-rays can create

Answer 20

farben centres

Question 21

how are farben centres created ?

Answer 21

X rays generate an ion and an electron.
the electron can sit in place in an anion vacancy. the electron based of schrodinger box theory has allowed energies which are within the UV range. when E releases energy then a colour is shown.

Question 22

what do defects do to the energy of the system?

Answer 22

increase it

Question 23

how do defects change the energy of the system

Answer 23

If an ion has to break 6 bonds but make 3 bonds then it is endothermic.
if a ion hops back into the vacant sit it is exothermic.

Question 24

what is wigners energy?

Answer 24

energy of defects recombined.

Question 25

how did the wigners energy nearly cause nuclear fall out in england

Answer 25

Two types of interstitial vacancy form - one with four bonds and one with three. These are highly mobile at room temperature
These have a barrier to recombination of 1.4eV and will release 12eV
These are probably the main cause of Wigner energy release

Question 26

what is wigners effect?

Answer 26

the displacement of atoms in a solid caused by neutron radiation. this increases the energy of system