For reference data you can search powder diffraction databases. I used < http://www.fiz-karlsruhe.de/icsd.html >. If you want to know the values for your sample, the best method is X-Ray diffraction.

Hi Anantha, I agree with Dieter, X-ray and Neutron diffraction are probably most suited if only the lattice constant is of interest. You can simulate powder patterns e.g. using powder cell, the required input parameters are the unit cell and the occupation of the sites within the unit cell (here is the download link, this is a very useful freeware software http://www.bam.de/de/service/publikationen/powder_cell_a.htm). However, if you want to know more about the structure, then some additional structure resolving methods such as X-ray absorption spectroscopy are useful, because it is difficult to resolve the small scattering differences e.g. between Cu and Zn in these structures (especially in the case of CZTS) by X-ray diffraction alone. Here the element sensitivity of EXAFS and XANES and the ability to use several different absorption edges give much additional information!

Good luck, Dirk

thank you Dr. Dieter and Dr. Dirk for your valuable notes..

i will look into the software and notes you have given

Yes of course, you can use a DFT code to determine the energy versus lattice parameter, and then look at the energy minimum.