Pressure as a probe of the glassy properties of disordered ferroelectrics, antiferroelectrics and dielectrics

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Abstract
Frustration-induced disorder and impurity-induced disorder can lead to the formation of a glassy state in ferroelectric (FE) and antiferroelectric (AFE) crystals. This paper highlights the important role of hydrostatic pressure as a variable for delicately tuning interatomic interactions and for understanding the short-range interactions and correlations responsible for the glassy state in disordered systems. Specifically, summaries and a comparison of novel glassy properties of mixed hydrogen-bonded FE and AFE crystals [Rb1-x(NH4)xH2PO4] which exhibit frustration-induced disorder and perovskites with dilute substantial impurities (KTa1-xNbxO3 for x≤0.02) are given. The properties of these materials are contrasted with those of more conventional orientational glasses in disordered dielectrics. Features of the results which have broad implications for the glassy state are discussed. These include (1) the pressure-induced crossover from long-range FE order to glassy behavior in soft mode systems, (2) the applicability and generality of the Vogel-Fulcher equation for treating the temperature and pressure dependences of the dipolar relaxation time, and (3) a unique manifestation of the non-equilibrium nature of the glass transition in high pressure measurements.