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The relaxation processes in pure and copper-doped potassium tantalate niobate (KTN) were investigated by dielectric spectroscopy over a wide frequency and temperature range. In the copper-doped KTN above the ferroelectric phase transition temperature, a relaxation process was observed to behave according to the Vogel-Fulcher-Tammann model. This process was not observed in the pure KTN crystal. Following the Adam-Gibbs theory of glass-forming liquids, this behavior was attributed to a cooperative rearrangement of dipolar clusters that are formed by off-center niobium ions around the copper impurity ions. This interpretation was substantiated by the observed difference in the configurational entropy between Cu-doped KTN and pure KTN crystals derived from differential scanning calorimetry measurements.
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Ishai et al. (2004) studied this question.
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