Complex mixed-ion pervoskites, ferroelectric material (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3, attract plenty of applications due to high piezoelectric response. The difficulties result from the complex real structure which in their relaxor state consists of two types of ordered nanodomains, chemical and polar, occuring in the disordered matrix.Thus,the elucidation of the competition between chemical order, local polar region and long range order, and their respective length scales is a long-standing and central problem in relaxors.Our goal is to combine the multitemperature neutron data with the existing X-ray data for quantitative modeling of the diffuse scattering and extend this work beyond the pure PMN compounds to solid solutions of PMN-PT.Information about local structure (diffuse scattering) is needed for sounder contribution of the full picture in this disordered system.