Quantum effects and glass-like behavior in ferroelectric oxides

Abstract

Quantum fluctuations, or zero-point motions, can strongly influence the low temperature response of a system near a structural phase transition. Among the manifestations of quantum fluctuations at ferroelectric phase transitions are different critical exponents, the suppression of the transition temperature, T c, below its classical value and the development of a quantum paraelectric state. To study these quantum effects as well as the crossover from the classical to the quantum regime, it is necessary to shift T c continuously from high to low temperatures. Hydrostatic pressure is an excellent variable for doing so. Results on the mixed oxides K 1− y Na y TaO 3 and KTa 1− x Nb x O 3 for fixed y and x will be summarized and discussed to illustrate some of the essential features. Some of these mixed oxides, as well as simpler oxides, exhibit short-range dipolar correlations and glass-like responses. An important current debate is centered around the question of whether or not the low temperature phase of these systems results from the freezing in of short-range order. Results on KTa 1− x Nb x O 3 oxides will be discussed and contrasted with other oxides. A novel pressure-induced crossover from normal ferroelectric ordering to dipolar glass behavior in soft TO mode systems with dilute impurities will be discussed, and possible experimental evidence for such a phenomenon will be presented.