Due to their exceptional ferroelectric properties, lead-based perovskite materials (PbB'B''O3) have been the subject of numerous studies. The different solid solutions exhibit their highest electromechanical responses for compositions lying at the so-called morphotropic phase boundary (MPB) between the rhombohedral (R3m) and tetragonal (P4mm) phases. Ferroelectric properties are dependent on 3 variables: applied electric field, temperature and mechanical stress σij. The effect of hydrostatic pressure on the physical properties of ferroelectrics is actually under intense investigations. In technological applications, large stress fields can be observed in miniaturized components or in ferroelectric dots. Additionally in the literature, experiments and theoretical calculations have indicated the existence of an intrinsic short range dynamical disorder over nearly the entire lead-based perovskite materials systems. Therefore the structural and dynamical behavior of lead-based perovskite materials as a function of P,T,E has to be entirely considered in the fundamental understanding of the ferroelectric-to-ferroelectric and ferroelectric-to-paraelectric phase transitions of such important technological materials. Based on neutron diffraction, X-ray diffraction, dielectric measurements, resonance Raman spectroscopy and X-Ray absorption Spectroscopy, we will present an overview of our new results.