Example - 123-high Tc superconductors
(\\erice_server – YBCO texture\ybco.zip)
• CuKa Bragg-Brentano diffractometer (Siemens)
• sample back packed in holder
• high quality data collection - used in original publication by
(Phys. Rev. B37, 7960-7962, 1988)
• presumably platy habit crystals - texture or “preferred
orientation” about 001
• Question – how to refine the texture (preferred
orientation?
• Do Rietveld refinement with different texture models
March-Dollase
Spherical Harmonics - cylindrical sample symmetry
• No texture model
• Poor fit - Rwp = 10.4%
• Especially some peaks!
• Harmonic Model L=6
• Much better fit - Rwp = 8.3%
• Not a lot different from MD and
L=4 fits
Refinement of YBa2Cu3O7-d X-Ray Powder Data
with Texture
Residuals for Various Texture Models
0.105
0.1
R
wp
0.095
0.09
0.085
0.08
0.075
no PO
no. parms
20
22
H L=2
25
H L=4
29
H L=6
34
H L=8
MD
21
• Great improvement of the fit
• March-Dollase better than L=2 Harmonic model
• L=6 Harmonic model about optimum
POLFPLOT - Radial Distribution for Harmonic Model L=6
Cut through pole figure – axial distribution
Pole figure – projection down z-sample axis
Hkl = 001
Normal
001 pole distribution
In plane
100 pole distribution
Makes sense! Crystals are plates with 001 normals
perpendicular to BB sample surface