Thank you very much Sir. But in this case composition of the materials are not playing any important role. Only the direction of  SiGe (67.93) and Si (69.13) in XRD  are given . Out of plane lattice mismatch was easily found by using  n *lamda= 2d sin theta and d= a/(h^2+k^2+l^2)^0.5.

Using these supplied data(percentage of composition is not given) we have to find out in plane lattice mismatch of Si and SiGe assuming SiGe layer is pseudomrphically grown on Si.

Thanks

shantanu