Example - 123-high T c superconductors ( \\erice_server – YBCO texture\ybco.zip)
description
Transcript of Example - 123-high T c superconductors ( \\erice_server – YBCO texture\ybco.zip)
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-DollaseSpherical 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
0.075
0.08
0.085
0.09
0.095
0.1
0.105
no PO H L=2 H L=4 H L=6 H L=8 MD
Residuals for Various Texture Models
Rw
p
Refinement of YBa2Cu3O7-d X-Ray Powder Data with Texture
• Great improvement of the fit • March-Dollase better than L=2 Harmonic model• L=6 Harmonic model about optimum
no. parms 20 22 25 29 34 21
POLFPLOT - Radial Distribution for Harmonic Model L=6
Hkl = 001
Normal In plane
Cut through pole figure – axial distribution
Pole figure – projection down z-sample axis
001 pole distribution
100 pole distribution
Makes sense! Crystals are plates with 001 normalsperpendicular to BB sample surface