INFLUENCE OF LATTICE IMPERFECTIONS ON THE TRANSITION-TEMPERATURES OF STRUCTURAL PHASE-TRANSITIONS - THE PLATEAU EFFECT

The influence of defects on the apparent phase transition temperature has been studied over a large range of defect concentrations. An interval was found for low concentrations (around 1 mol%) in which the transition temperature depends only weakly on the number of defects and where defect tails occur. This interval is called the plateau. For higher defect concentrations we find that chemical mixing leads to strong variations of the transition temperature which are well described in the approximation of a homogeneous crystal. Experimental results on lead-phosphate doped with Ba, Pb doped zirconium titanate and omphacite solid solutions are discussed within mean field theory of strongly localised defects and Ornstein-Zernike response functions. Renormalisation of the order parameter saturation at low temperatures and changes of the diplacive or order/disorder behaviour of the phase transition are predicted. © 1991, Taylor & Francis Group, LLC. All rights reserved.