Hi Maithili K Rao,

There is no specific rule but there are a number of factors as well as tweaks & tricks one needs to know for the lattice parameter calculation (generally by Reitveld refinement using different software). Please find some of the files which could be helpful.

Thanks & regards

MN

I agree with Mithun Nath .

1 Basics of X-Ray Powder Diffr action.pdf

Dear Maithili K Rao,

Have in mind that, using Rietveld refinement, the precision of your determination is going to decrease as the number of phases increases inside de sample.

As you may realize, the intensity of the peaks can not be straight related to the quantity.

There are several reasons, the diffraction plane contains atoms in interstitial positions, for instance. They contribute to increasing intensities, however not related to the primary phase quantity. It relates to increasing diffraction centers only.

The structural factor is the entity to be considered for intensity relationship. It contains all atoms belonging to a specific plane in the form of cumulative contributions.

In the case of more than one phase, long-range 2theta measurements are mandatory, as the overlap probability is increased. More extended range increases the possibility of observing not overlapped peaks.

Ideally, use as many peaks of a single-phase as possible; you have the opportunity of correcting specimen displacement, zero shifts as an erroneous instrumental contribution, as well as significant systematic errors, not related to you quantification pathway, but the instrumental.

Be aware, substitutional and interstitial atoms interfere in the lattice parameter calculations as much as others physical parameters like high pressure and measurements over a broad temperature range. Especially if the measurement is going to be compared afterward, the conditions must be severely controlled.

As for looks like your samples are natural ones, solid-solutions are of significant probability, depending only on the lithodomain of the samples.

As more than one phase is present, search the peaks carefully, with a proper phase identification software, avoiding false-positive occurrences.

Once precisely determined the positions of the peaks, you may fit the diffraction to result in more accurate relative quantities.

Avoid using strongly overlapped peaks, is not worth it.

Check the algorithm result, and you are interested in phase wt%.

Once all data are available, it is reasonable to refine the phase's lattice parameters.

Take care of the interdependency of the parameters, if the unstable fit is observable, fix/release one by one, and check your result. Some fitting software allows the visualization of the correlation matrix, quite useful to determine the interdependencies. Avoid them, use contour conditions if necessary.

Best regards

WNM

Here is an easy example for the same,

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