Hello B Mohan Rao

In order to use Braggs's Law correctly, you must set the correct wavelength used in experiment. Could you please provide the details of your calculation and the reference value?

Best regards,

Ricardo Tadeu

Dear B Mohan Rao ,

in addition to the answer of Ricardo Tadeu Maia

you should consider experimental issues which will cause peak shifts such as for example an off set in the angular (theta) scale or shifts due to not optimal sample height adjustment. In the latter case you will have a cos(theta)-dependence of the peak shift(s)*).

From the wellknown lattice constant of austenite and your x-ray wave length you are able to calculate the expected the peak positions and thus your peak shift(s) with respect to these expectations. You can check whether there is a constant shift or a cos(theta) dependence. Just check the ratio of these shifts...

*) see for example

Presentation XRD and XRR angular shifts due to sample height variations

or

equation 17 of

Article X-Ray Diffraction Techniques for Mineral Characterization: A...

Good luck and

best regards

G.M.

You should show the XRD plot and state all experimental parameters as well as how you identified the peaks, otherwise it is imppossible to thelp you.

We actually don't need all experimental details to help you, if you can use equations, rather than having us do the math for you.

One approach would be to fit the peaks and use the estimated error in the fits to calculate d with estimated uncertainty for each peak, then lattice parameter a with estimated uncertainty from each peak. Then calculated weighted average with weighting given by inverse of variance (squared estimated uncertainty).

But a better method is to use the fact that conventional diffractometers have typical angle errors that are not the same across the whole diffraction pattern. These have been characterized and several different extrapolation schemes have been developed. Look up "high accuracy lattice parameter measurement" in Cullity's index. My favorite is the Nelson-Riley extrapolation. Google that.

You would really prefer more peaks! But using that analysis will probably give you the best estimate with your current data.

Be sure to run an angle calibration standard in your diffractometer and use that to correct your raw data for best results.