'Dirty' displacive ferroelectrics

Using the powder Raman technique we have measured most of the lattice vibrational modes in the Pb1-xLaxTi1-x/4O3 perovskite solid solution series. From the data for these disordered systems the clamped dielectric constant at zero frequency, ε{lunate}m, was determined and compared with the clamped dielectric constant, ε{lunate}cap, measured by standard capitance techniques. We find that ε{lunate}cap/ε{lunate}m exceeds one, and increases as the transition temperature is approached from below. Strikingly, we also find similar behavior for the 'classical' ferroelectrics BaTiO3, LiNbO3 and LiTaO3, as well as for ferroelectrics with the tungsten bronze crystal structure. © 1973.