Time‐ and Frequency‐Dependent Surface Transport on Humid Insulators

Abstract

Measurements are reported, we believe for the first time, of the dynamic surface conduction on humid insulators, resolved as complex impedance plots in the frequency range 0.01-10 kHz, and also of the corresponding time dependence of the charging and discharging currents in the time interval between 100 ~s and many hours, with a range of step voltage amplitudes. The aspect ratio of the surface electrode configuration has been varied over three decades and the magnitude of the impedance, instead of being linear in this ratio as in the classical surface conduction with a uniform surface conductance, is found to follow a power law at small values of this ratio and an exponential law at larger values, suggesting the presence of surface dispersion. The conductance is also exponentially dependent on the relative humidity of the ambient air, suggesting the importance of percolation phenomena. The charging and discharging currents vary very slowly in time and their magnitudes are strongly nonlinear in the amplitude of the step voltage, pointing clearly to the importance of electrochemical storage of charge and of energy, as distinct from the classical electrostatic processes. Phenomena of negative capacitance are seen in certain circumstances. Probing of the space between the electrodes shows the surface potential to be distributed and not to be predominantly concentrated at the electrodes. The behavior of glass, mica, and silicon nitride was found to be very similar. The significance of these observations is discussed in terms of a model involving nonuniform filamentary conduction paths on the humid surfaces.

The dielectric properties of humid cellulose

“…The decay at time t r will (in logarithmic representation) become more gradual and extend backwards to shorter times. Such characteristics have been observed in time domain measurements on solid ionic conductors [39,40] and humid conducting surfaces [16,17,41].…”

“…Experimental data in the literature show striking similarities over a wide range of materials, including exponential dependence of low frequency conductivity on N À1/3 [1,2]. Low frequency dielectric data showing rapid increases of magnitude with decreasing frequency have been widely reported for hydrophilic solids [3][4][5][6][7][8][9][10][11][12][13][14][15] and for humidified surfaces [16,17]. Many of these data show linearity in log-log graphs and, where reported, a constant phase angle over many decades of frequency.…”

Ferroelectric properties of lanthanum and titanium modified SBN ceramic system

“…Contribution of humidity to permittivity is indeed a familiar fact in the literature. Dipolar orientation and low frequency dispersion are just two examples of mechanisms that characterize water vapor activity in solid state materials [15][16][17]. Figure 4 summarizes the permittivity versus temperature curves, measured at 1 kHz, for the three samples.…”

Microstructure and gas sensing properties of the ZnO thick film treated by hydrothermal method

“…6(a)-(d). The impedance curves below 400 Hz, which were disordered or looped due to the so-called negative capacitance effect [29], could be ignored.…”