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Activation energies (Ea) for electrode and grain boundary (GB) conduction are found to be greater than that of the bulk conduction. This implies that both electrode and GB act as two insulating barriers affecting conductivity and dielectric relaxations in KxTiyNi1-x-yO. Decrease in Ea for electrode conduction above T>295 K leads to relatively greater loss due to the dc-charge transportation between electrodes and dielectric. The Cole-Cole equation has been modified to explain [variant_greek_epsilon]′ over a wide range of frequency (10–107 Hz). Impedance spectroscopic study has also been employed to distinguish electrode relaxation from GB relaxation. [ABSTRACT FROM AUTHOR]

Dielectric permittivity at different polarizing states during field driven ferroelectric-ferroelectric (F-F) transition and the dielectric relaxation spectra in the antiferroelectric liquid crystal (AFLC) phase have been studied to elucidate the interaction processes involved during the transition. The unwinding process of antiferroelectric helix has been found to be governed by the polar coupling between the applied field and the antiferroelectric polarization vector followed by nonpolar interaction with the dielectric anisotropy of the tilted molecules. Frequency dependence of the permittivity-voltage hysteresis behavior observed during the F-F transitions is concluded to be due to different relaxation processes involved in the AFLC phase. [ABSTRACT FROM AUTHOR]

The KxTiyNi1-x-yO system in the series AxTiyNi1-x-yO (A=Li, K, Na; x=0.05–0.30, y=0.02) shows the highest dielectric constant [variant_greek_epsilon]′∼105 and lowest loss. The high [variant_greek_epsilon]′ value is attributed to microstructures, which form boundary layer capacitors. Electrical conductivity in these materials follows small polaron hopping mechanism in the nonadiabatic regime. Unlike LixTiyNi1-x-yO and NaxTiyNi1-x-yO (NTNO), KxTiyNi1-x-yO (KTNO) exhibits an anomaly around Tp∼430 K. Tp shifts to the lower temperature range with increasing K content which is related to the higher ionic radius of K. [ABSTRACT FROM AUTHOR]

With increasing the Li doping level in La[SUB0.7]Ca[SUB0.3-y]Li[SUBy]MnO[SUB3] (0⩽y⩽0.3), the system is driven from a higher-conductivity regime to a lower-conductivity regime, which is in sharp contrast with the behavior of Na or K doping. Compared to those of K or Na, the ionic radius of Li is much smaller than that of Ca. Therefore, substitution of Ca by Li results in a smaller average A-site radius, narrowing the bandwidth and hence enhancing the band gap and resistivity. The effect of random disorder of La[SUP3+] and A[SUP2+] also plays an important role leading to charge localization. [ABSTRACT FROM AUTHOR]

Dielectric permittivity at different polarizing states during field driven ferroelectric-ferroelectric (F-F) transition and the dielectric relaxation spectra in the antiferroelectric liquid crystal (AFLC) phase have been studied to elucidate the interaction processes involved during the transition. The unwinding process of antiferroelectric helix has been found to be governed by the polar coupling between the applied field and the antiferroelectric polarization vector followed by nonpolar interaction with the dielectric anisotropy of the tilted molecules. Frequency dependence of the permittivity-voltage hysteresis behavior observed during the F-F transitions is concluded to be due to different relaxation processes involved in the AFLC phase. [ABSTRACT FROM AUTHOR]