Hiya
all
I've come across a
unit cell that seems to give alot of software a headache when generating the
powder patterns. I've tested 6 software packages with this (including
commercial) and found only a 50% success rate in generating a good pattern with
correct relative intensities. Not sure where the problem lies with the
'faulty' software, maybe some of the hkl multiplicities are off.
The cell is in space
group P3112 and is a �3a x �3a
supercell of a nice boring simple R-3m layered structure. It's quite a
pretty structure and when the metals are similar in scattering power you'd
expect a very similar diffraction pattern to the R-3m (identical if all of the
TMs are the same). Doesn't always happen though. If you're curious
try making these 2 cif files and seeing what your software churns
out. There aren't even any structures with this space
group in the ICSD (not even the other enantiomorph P3212), and only a few in the
PDF2, so it's not exactly a fatal flaw. Might make it worth checking
some other trigonal space groups though if your software fails this one.
BTW I am well aware that quartz has the P3221/P3121 chiral structures, and
that any software worth its salt gets that one right!
Have fun!
Pam
_chemical_formula_sum 'Li3 Mn Ni Co O6'
_cell_length_a 2.8600
_cell_length_b 2.8600
_cell_length_c 14.3000
_cell_angle_alpha 90.000
_cell_angle_beta 90.000
_cell_angle_gamma 120.000
_symmetry_space_group_name_H-M 'R -3 m'
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_occupancy
_atom_site_B_iso_or_equiv
Li1 Li 0.0000 0.0000 0.5000 1.000 1.00000
Mn1 Mn 0.0000 0.0000 0.0000 0.333 1.00000
Ni1 Ni 0.0000 0.0000 0.0000 0.333 1.00000
Co1 Co 0.0000 0.0000 0.0000 0.333 1.00000
O1 O 0.0000 0.0000 0.2560 1.000 1.00000
_chemical_formula_sum 'O18 LI9 NI3 CO3 MN3'
_cell_length_a 4.9537
_cell_length_b 4.9537
_cell_length_c 14.3000
_cell_angle_alpha 90.00
_cell_angle_beta 90.00
_cell_angle_gamma 120.00
_symmetry_cell_setting Hexagonal
_symmetry_space_group_name_H-M 'P 31 1 2'
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_occupancy
_atom_site_B_iso_or_equiv
Li Li 0.77780 0.22220 0.83330 1 1
Li Li 0.11110 0.88890 0.83330 1 1
Li Li 0.44440 0.55560 0.83330 1 1
Ni Ni 0.77780 0.22220 0.33330 1 1
Co Co 0.11110 0.88890 0.33330 1 1
Mn Mn 0.44440 0.55560 0.33330 1 1
O O 0.44440 0.22220 0.25600 1 1
O O 0.11110 0.22220 -0.07730 1 1
O O 0.11110 0.55560 0.25600 1 1
Dr Pamela Whitfield CChem MRSC
Energy Materials Group
Institute for Chemical Process and Environmental Technology
Building M12
National Research Council Canada
1200
Montreal Road
Ottawa ON K1A
0R6
CANADA
Tel: (613) 998 8462 Fax:
(613) 991 2384
Email:
<mailto:[EMAIL PROTECTED]>
ICPET WWW: http://icpet-itpce.nrc-cnrc.gc.ca
