A new low-temperature state in a La-modified lead zirconate titanate relaxor

Several anomalies are observed in the relaxer system Pb0.91La0.09 Zr0.65Ti0 .35O3 at low temperature for the first time: a boson peak in the Raman scat tering at frequencies below 100 cm(-1), and extrema in the dielectric permi ttivity and pyroelectric current near 45 K. Calculations show that these an omalies are connected with a polarization-deformation coupling via electros triction. Due to this coupling, the new low-temperature glassy state is cal led an "improper dipole glass". The generality of the proposed model sugges ts that similar states should also exist in other disordered ferroelectrics .