Hello everyone!
I suppose the XRD of sample LaPO4 has some anisotropic line broadening along [h00]. How could I model the shape of particle using WPPF method or something else? Diffraction pattern processing has informed about parameters P0-P5, which correlate with parameters b11, b22 etc., in SmartLab Studio II by Rigaku. We have opportunity to save the report in FullProf, but I've no idea how to depict a particle of a specific diffractogram.
I attached XRD, SEM pattern and some theory for the proof
Dear Maria Enikeeva ,
Some considerations:
A sphere is perfectly isotropic; therefore, the mean column length is the same for every lattice direction and diffraction peak in an XRD pattern.
For other shapes, the mean column length will depend on the crystal's direction and vary more or less from reflection to reflection.
Apart from the shape of the crystallite and the crystallographic direction, the shape of the diffraction peak profile, the definition of the profile width, and the crystallites' size distribution all play a significant role in the texturized sample. The presence of a size distribution implies that integral methods like XRD will usually give some mean value for properties like "size" and "shape."
To model the shape of particles, using WPPF is necessary to access the descriptors of the anisotropy.
You may restrict your analysis to families of reflections for the principal crystal directions like h00, 0k0, and 00l, as mentioned.
However, this is not a complete pattern analysis, is omitted the mixed reflections' information.
For proper whole pattern fitting, it is necessary a model which includes the treatment of intermediate reflections. Cylindrical or ellipsoidal models for size anisotropy are applied to overcome the problem.
Whole Powder Pattern Fitting (WPPF) tries to fit the observed diffraction pattern using pre-defined peak shape functions.
In contrast, a Rietveld refinement of a crystal structure may work as well with empirical profiles. Ideally, we hope to get both crystal structure and microstructure (size-strain) information from a single fit; nevertheless, real systems often have to sacrifice one.
Whole Powder Pattern Modelling (WPPM) takes a different approach. Based on some physically based priory assumptions, the complete peak profiles are considered.
In contrast to WPPF, WPPM can deal with effects like stacking faults.
A Particle Shape Quantities and Measurement Techniques - A review, December 2012, Electronic Journal of Geotechnical Engineering 18(A):169 have interesting points.
The mentioned factors are anisotropic temperature factors, B11, B22, B33, B12, B13, B23 as treated in Fullprof suite, to simulate or fit the X-ray diffraction. It is essential to mention that anisotropic displacement (temperature) parameters, βij are all refinable for X-ray or nuclear Neutron scattering.
In the fullprof suite, you may enter all descriptors manually and in the top command line, choose the pattern simulation instead of the fitting. The Fp_Studio, a taskbar program inside Fullprof Suite, is used to visualize the crystal and magnetic structures, considering all filled parameters. The input file for Fp_Studio has the extension ".fst" automatically generated after a structure refinement.
That procedure is straight forward if using the PCR editing software from the taskbar inside fullprof.
The shape or the morphology of a crystal may be visualized using public programs like VESTA, proprietary programs like Mercury from CCDC, Materials Studio from Biovia, or even the old SHAPE software.
Please pay attention to your choice; some of them will neglect the anisotropic temperature factors.
Best regards,
WNM
Dear Maria Enikeeva ,
Some considerations:
A sphere is perfectly isotropic; therefore, the mean column length is the same for every lattice direction and diffraction peak in an XRD pattern.
For other shapes, the mean column length will depend on the crystal's direction and vary more or less from reflection to reflection.
Apart from the shape of the crystallite and the crystallographic direction, the shape of the diffraction peak profile, the definition of the profile width, and the crystallites' size distribution all play a significant role in the texturized sample. The presence of a size distribution implies that integral methods like XRD will usually give some mean value for properties like "size" and "shape."
To model the shape of particles, using WPPF is necessary to access the descriptors of the anisotropy.
You may restrict your analysis to families of reflections for the principal crystal directions like h00, 0k0, and 00l, as mentioned.
However, this is not a complete pattern analysis, is omitted the mixed reflections' information.
For proper whole pattern fitting, it is necessary a model which includes the treatment of intermediate reflections. Cylindrical or ellipsoidal models for size anisotropy are applied to overcome the problem.
Whole Powder Pattern Fitting (WPPF) tries to fit the observed diffraction pattern using pre-defined peak shape functions.
In contrast, a Rietveld refinement of a crystal structure may work as well with empirical profiles. Ideally, we hope to get both crystal structure and microstructure (size-strain) information from a single fit; nevertheless, real systems often have to sacrifice one.
Whole Powder Pattern Modelling (WPPM) takes a different approach. Based on some physically based priory assumptions, the complete peak profiles are considered.
In contrast to WPPF, WPPM can deal with effects like stacking faults.
A Particle Shape Quantities and Measurement Techniques - A review, December 2012, Electronic Journal of Geotechnical Engineering 18(A):169 have interesting points.
The mentioned factors are anisotropic temperature factors, B11, B22, B33, B12, B13, B23 as treated in Fullprof suite, to simulate or fit the X-ray diffraction. It is essential to mention that anisotropic displacement (temperature) parameters, βij are all refinable for X-ray or nuclear Neutron scattering.
In the fullprof suite, you may enter all descriptors manually and in the top command line, choose the pattern simulation instead of the fitting. The Fp_Studio, a taskbar program inside Fullprof Suite, is used to visualize the crystal and magnetic structures, considering all filled parameters. The input file for Fp_Studio has the extension ".fst" automatically generated after a structure refinement.
That procedure is straight forward if using the PCR editing software from the taskbar inside fullprof.
The shape or the morphology of a crystal may be visualized using public programs like VESTA, proprietary programs like Mercury from CCDC, Materials Studio from Biovia, or even the old SHAPE software.
Please pay attention to your choice; some of them will neglect the anisotropic temperature factors.
Best regards,
WNM
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