Elastic strain and stress determination by Rietveld refinement: generalized treatment for textured polycrystals for all Laue classes

A novel approach to model diffraction line shifts caused by elastic residua l or applied stresses in textured polycrystals is proposed. The model yield s the complete strain and stress tensors as a function of crystallite orien tation, as well as the average values of the macroscopic strain and stress tensors. It is particularly suitable for implementation in Rietveld refinem ent programs. The requirements on refinable parameters for all crystal Laue classes are given. The effects of sample symmetry are also included and th e conditions for strain invariance to both the sample symmetries (texture a nd stress/strain) are discussed.