Incorporating the direct derivation method and molecular scattering power method into the Rietveld quantitative phase...

Area of Science:

• Crystallography
• Materials Science
• Analytical Chemistry

Background:

• Conventional Rietveld quantitative phase analysis (QPA) requires complete knowledge of crystal structures.
• Existing methods like the direct derivation method (DDM) and unit-cell scattering power method have limitations.
• There is a need for methods that can analyze mixtures containing phases with partially or unknown crystal structures.

Purpose of the Study:

• To develop and evaluate hybrid QPA methods that integrate with conventional Rietveld analysis.
• To introduce the Ck-corrected direct derivation method (DDM) and the molecular scattering power (MSP) method.
• To assess the accuracy of these hybrid methods for analyzing complex mixtures.

Main Methods:

• Reviewing equations for DDM and unit-cell scattering power method.
• Developing Ck-corrected DDM and MSP methods.
• Integrating these methods into a hybrid QPA routine within TOPAS software.
• Evaluating accuracy using calculated patterns, IUCr CPD-1 dataset, and synthetic mixtures of clay minerals and corundum.

Main Results:

• Hybrid QPA methods enable simultaneous fitting of known and partially/unknown crystal structures.
• Accuracies of hybrid methods are slightly lower than conventional Rietveld QPA, with deviations < 3 wt%.
• Ck correction improves DDM accuracy, especially for mixtures with varying average atomic numbers.
• MSP method removes the need for lattice parameters, unit-cell volume, or molecule count.

Conclusions:

• The Ck-corrected DDM and MSP methods provide accurate quantitative phase analysis for complex mixtures.
• These hybrid methods enhance the applicability of Rietveld analysis to materials with unknown structural information.
• The developed methods offer a valuable advancement in materials characterization and analysis.