Dipole ordering effects and reentrant dipolar glass state in KTaO3:Li, Nb

Dielectric permittivity and Raman-scattering studies reveal unconventional dipole ordering and structural effects that arise in the incipient ferroelectric KTaO3 due to the simultaneous presence of off-center Li+ and Nb5+ ions. A soft-mode-driven transition into a ferroelectric phase accompanied by the formation of a dipole glass in the Li+ subsystem was identified at 39 K in a sample of composition K0.9986Li0.0014Ta0.988Nb0.012O3. A second soft-mode transition was found at 30 K. whereas a transition into a phase identified as a "reentrant dipolar glasslike state" was observed at 15 K. Such a sequence of phases, diordered-long range ordered-reentrant glass, already known for disordered ferromagnets. is here reported for a highly polarizable matrix with soft modes.