Dielectric constant and ordering effects of pure and doped KTaO3 quantum paraelectric; Cu-codoping enhancement effect

Abstract

epsilon'(T, f) and tan[delta(T, f)] spectra (10-300 K, 120 Hz-1 MHz) of pure KTaO3 (KTO), KTO:Li (0.1-3%), KTO:Fe 1%, KTO:Cu 0.83% below 70 K reveal a Debye-like universal Arrhenius relaxation with Delta approximate to 80-85 meV, tau(0) similar to 5 x 10(-14) s. In KTO:Li Fe and KTO:Li Cu this contribution increases, confirming dipole-pair ordering effects with the leading role of Li+ in pair relaxation (V. Trepakov er al., J. Phys.: Condens. Matter 7, 3785 (1995)). A dramatic Cu-codoping dielectric enhancement effect in KTO: Li Cu was observed. In KTO:Li 3% Cu 0.2% in region 50-60 K epsilon'(T) reveals a maximum of similar to 10(5), accompanied by temperature hysteresis and dielectric loops. Ferroelectric-type phase transition with a critical dynamic central peak, induced by Cu2+(Ta)V-O centers as a slowest relaxator or oscillator in KTO:Li, is considered as an epsilon' enhancement cause. A possibility of incommensurate phase induced by Cu2+-V-O centers and cluster-induced cooperative behavior is discussed too.