Low temperature structural transformations of dilute KTa 1–x Nb x O 3 : x = 0.018, quantum superparaelectric or reentrant glass scenario?

Abstract

Impurity induced structural transformations are studied for KTa{sub 1-x}Nb{sub x}O{sub 3} with x = 0.0018 (KTN-1.8) by low-frequency linear and non-linear dielectric spectroscopy techniques. Nb admixture leads to the appearance of a sharp {var_epsilon}{prime}(T) maximum accompanying the ferroelectric phase transition at T{sub C} {approx} 27 K, and a glass-like state formation at lower temperatures. The linear permittivity evidences properties inherent to systems being near the quantum-mechanical displacive limit and shows the long range polar order with macroscopic polarization formation at {approx}27 K. This conclusion was proven by nonlinear polarization response stuidy under dc electric field action, which evidenced also the proximity of the three-critical point. Above 27 K, the nonlinearity increases at cooling in accordance with the Devonshire theory for the paraelectric phase of conventional ferroelectrics. Below 27 K, the random distribution of Nb{sup 5+} ions and related system's inhomogeneities provoke a new low temperature phase state formation, which can be treated as reentrant polar-glass.