The problem:

Structure of Li2CoPO4F cannot be solved or

refined from bulk diffraction.

The solution:

Precession electron diffraction càn get the

job done.

This presentation describes the procedure

in the shortest way possible.

For a more detailed treatment:

“Solving the Structure of Li Ion Battery Materials with

Precession Electron Diffraction: Application to Li2CoPO4F”

in Chemistry of Materials

by Joke Hadermann, Artem M. Abakumov, Stuart Turner,

Zainab Hafideddine, Nellie R. Khasanova, Evgeny V. Antipov

and Gustaaf Van Tendeloo

Published online July 11, 2011

http://pubs.acs.org/doi/abs/10.1021/cm201257b

First, electron

diffraction patterns are

taken, using the

precession attachment.

Non main zones have

more reliable peak

intensities than main

zones.

All patterns can be indexed using the cell

parameters and space groups known from XRD:

a= 10.452(2) Å, b= 6.3911(8) Å, c=10.874(2) Å

Pnma

The intensities of the observed peaks are extracted

(ELD software).

Treated: symmetry equivalent reflections merged,

geometric corrections applied

We now have intensities of

237 symmetry unique reflections

Merged into one list (Triple software)

Intensities of 237

symmetry unique

reflections

a= 10.452(2) Å,

b= 6.3911(8) Å,

c=10.874(2) Å

Pnma

&

INTO

Direct Methods

Result: R=31%

CO and P positions similar to Li2FePO4F

but

Li, O, F mixed over remaining positions

Assign

F: tetrahedra around P

O: complete the octahedra around Co

Remaining positions (purple) Li or ghosts?

Difference Fourier maps including Co,P,O,F

The difference Fourier maps

clearly show the real peaks

The Li-atoms are now also located

Straight from direct methods:

too many Li(?) peaks

Difference Fourier allows

to eliminate the grey ones

Structure is solved !

Can be refined...

Separate list of intensities per zone were

put into Jana using separate scale factors

for each list on input

Use PO4 rigid units:

18 variables reduced to 6

R=24% (reasonable for precession

electron diffraction data)

&

PED can be successfully applied

for the crystallographic characterization

of Li-based battery materials

Conclusion

Li2CoPO4F was successfully solved and

refined from precession electron

diffraction