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Example - 123-high T c superconductors ( \erice_server – YBCO textureybco.zip) CuK a Bragg-Brentano diffractometer (Siemens) sample back packed in holder high quality data collection - used in original publication by ( Phys. Rev. B37, 7960-7962, 1988)
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Example - 123-high Tcsuperconductors • (\\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-dX-Ray Powder Data with Texture no. parms 20 22 25 29 34 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 = 001 001 pole distribution In plane Normal 100 pole distribution Makes sense! Crystals are plates with 001 normals perpendicular to BB sample surface