When the intensity of the highest peak in a Rietveld refinement does not match expectations, several strategies can be employed to address the issue. Here are some key considerations and steps to take:

1. Check for Preferred Orientation

• Preferred Orientation: If the crystallites in your sample are not randomly oriented, this can lead to intensity discrepancies. This phenomenon, known as preferred orientation or texture, often occurs with needle- or plate-shaped crystals. Consider using methods to quantify and correct for this effect, such as adding a preferred orientation model to your refinement3.

2. Refine Scale Factors

• Scale Factor Adjustment: The scale factor is crucial for matching observed and calculated intensities. If there is a significant mismatch, refining the scale factor can help improve the fit. Ensure that this is one of the first parameters adjusted during refinement23.

3. Examine Unit Cell Parameters

• Lattice Parameters: Incorrect unit cell dimensions can lead to poor intensity matches. Verify that your initial lattice parameters are accurate and refine them if necessary. This may involve checking the space group or re-evaluating the initial guesses used in the refinement62.

4. Adjust Background and Peak Profile

• Background Correction: Ensure that background contributions are accurately modeled as they can affect peak intensities across the entire pattern. Adjusting background parameters may help align observed and calculated intensities better4.
• Peak Profile Fitting: Use appropriate peak shape functions to model the peak profiles accurately. A poor fit can lead to intensity mismatches1.

5. Investigate Parameter Correlations

• Parameter Correlation Issues: Sometimes, correlated parameters can prevent effective refinement. If certain parameters are not converging, consider refining them individually rather than collectively to isolate the issue3.

6. Perform Le Bail or Pawley Refinement

• If intensity mismatches persist after addressing the above factors, consider conducting a Le Bail or Pawley refinement as a preliminary step. These methods focus on fitting peak positions and intensities without requiring a full structural model, which may help clarify issues before proceeding with full Rietveld refinement45.

7. Visual Inspection of Rietveld Plots

• Use Rietveld plots to visually assess discrepancies between observed and calculated patterns. This can help identify which peaks exhibit the largest deviations and guide subsequent refinements towards those specific parameters2.

By systematically addressing these factors, you can improve the match between observed and calculated intensities in your Rietveld refinement results.