Dielectric Properties of Cobalt Oxide, Nickel Oxide, and Their Mixed Crystals

Abstract

Dielectric constant κ′, loss κ″, and conductivity σ of single crystals of CoO, NiO, and mixed crystals of CoO–NiO as a function of frequency from 102 to 1010 cps and temperature from −193°C to 400°C have been determined. The dielectric constant κ′ is constant (12.9 at 25°C) in the whole frequency range in CoO. It decreases with frequency in NiO and mixed crystals CoO–NiO. In NiO κ′ reaches a constant value (11.9 at 25°C) at 105 cps, and in CoO·NiO (12.3 at 25°C) at 1010 cps. The dielectric constants extrapolated to 0°K are 10.9, 10.0, and 9.1 for CoO, CoO·NiO, and NiO, respectively. In all crystals the dielectric constant increases exponentially with temperature. Using modified Debye equations, two thermal activation energies for κ′ have been obtained: 0.042, 0.027, and 0.018 eV for temperatures below 40°C (frequency-independent region); 0.33, 0.20, and 0.16 eV for temperatures above 40°C, for CoO, NiO, and CoO·NiO (frequency-dependent region). The plot of log σ vs 1/T gives straight lines for CoO from 400° to 100°C, and NiO from 400° to 25°C with activation energies 0.73 and 0.66 eV. At lower temperatures the activation energies decrease continuously. The mixed crystals have two activation energies, one at high temperatures and the other at low temperatures. Variation of the activation energy with composition at high temperatures is less than that at low temperatures. The variation of activation energies in mixed crystals is correlated to lattice distortion and an increase of trivalent ion concentration.

Can the Point Defect Model Explain the Influence of Temperature and Anion Size on Pitting of Stainless Steels

“…The temperature dependence of r opt can now be found by differentiating with respect to temperature: (15) The fact that ( ) is negative means that an increase in temperature will favour pitting by smaller anions, i.e. it agrees with the experimental observation that chloride becomes more aggressive than bromide at higher temperatures.…”

Unusual Mott transition in multiferroic PbCrO 3

“…The measured dielectric constant, «′, is significantly reduced when the temperature is decreased because dielectric oscillators are thermally activated or when the frequency is increased ( Fig. 2A) because the space-charge polarization, which partially contributes to «′, is progressively suppressed at higher frequencies (33). Above T N , «′ is sensitive to the external magnetic field (B) at all selected frequencies, suggesting a strong magnetoelectric effect.…”

Investigation on growth, optical and thermal properties of stilbazolium derivative crystal: 4-N,N-dimethylamino-4′-N′-methylstilbazolium 2,4-dimethylbenzenesulfonate

“…It is observed that the dielectric constant and dielectric loss decrease with increasing frequency and attain saturation at higher frequencies. The low dielectric constant value of the crystal at high frequency is attributed to space charge polarization [25]. The very high value of dielectric constant at low frequencies is due to the presence of ionic, electronic and orientation polarizations.…”