CLUSTER AND DOMAIN-STATE DYNAMICS OF FERROELECTRIC SR1-XCAXTIO3 (X=0.007)

A high, rounded peak of the permittivity, max′6×104, at T18 K evidence a percolative-type phase transition into a random-field-induced ferroelectric domain state of the doped system Sr1-xCaxTiO3 (x=0.007). Dispersion measurements of the permittivity reveal strong polydispersivity of the system. Deviations from Arrhenius behavior below T=11 K indicate the onset of dissipative quantum tunneling of the Ca2+ dipoles between their different off-center positions. Anomalies in both the linear and the nonlinear dielectric permittivity are explained by the presence of two different dissipative cluster contributions. They are attributed to the reorientation of Ca2+-centered polar nanometer-scale regions within ferroelastic single domains of the system and to their interaction with coherent acoustic quantum fluctuations of the host lattice, respectively. © 1995 The American Physical Society.