Ionic conductivity and dielectric measurements in single crystal β---AgI

Ionic conductivity measurements have been made on pure, copper-doped and cadmium-doped single crystals. Dielectric measurements in the frequency range 30Hz–100Hz showed that there was no anomalously to be (0.64 ± 0.02) eV and migration energies for silver ion intersitials and vacancies in the c direction to be (0.41 ± 0.02) eV and (0.50 ± 0.02) eV respectively. ESR measurements have shown that copper exists as Cu+ in these crystals. Dielectric measurements in the frequency range (OHz–100KHz showed that there was no anomalously high value for ε as reported earlier.

High‐temperature phase transitions in pure and deuterated ammonium dihydrogen phosphate: Conductivity and dielectric measurements

Results of axiswise measurements of the electrical conductivity (dc and ac) and dielectric constant of NH4H2PO4 confirm the occurrence of the recently suggested high‐temperature phase transition in this crystal (at 133 °C). The corresponding transition in ND4D2PO4 observed here for the first time takes place at 141.5 °C. The mechanism involved in these transitions and those associated with the electrical conduction and dielectric anomalies are explained on the basis of the motional effects of the ammonium ions in these crystals. Conductivity values for deuterated crystals give direct evidence for the predominance of protonic conduction throughout the entire range of temperatures studied (30–260 °C).

Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni1–xZnxFe2O4, as well as the filler (Ni1–xZnxFe2O4) incorporated rubber ferrite composites (RFCs). Ni1–xZnxFe2O4 (where x varies from 0 to 1 in steps of 0×2) were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (sa.c.) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10–3 S/m. Analysis of the results shows that sa.c. increases with increase of frequency and the change is same for both ceramic Ni1–xZnxFe2O4 and RFCs. sa.c. increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of sa.c. on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples

A practical interpretation of dielectric measurements up to 100-mc.

"PB 161545."

Dielectric measurements on high-temperature materials

Prepared by Massachusetts Institute of Technology, Laboratory for Insulation Research, under USAF Contract F33615-67C-1612.

Simulation study for analysis of online dielectric measurement problems on transformer insulation system

Determining the condition as well as the remaining life of an insulation system is essential for the reliable operation of large oil-filled power transformers. Frequency-domain spectroscopy (FDS) is one of the diagnostic techniques used to identify the dielectric status of a transformer. Currently, this technique can only be implemented on a de-energized transformer. This paper presents an initial investigation into a novel online monitoring method based on FDS dielectric measurements for transformers. The proposed technique specifically aims to address the real operational constraints of online testing. This is achieved by designing an online testing model extending the basic “extended Debye” linear dielectric model and taking unique noise issues only experienced during online measurements into account via simulations. Approaches to signal denoising and potential problems expected to be encountered during online measurements will also be discussed. Using fixed-frequency sinusoidal excitation waveforms will result in a long measurement times. The use of alternatives such as a chirp has been investigated using simulations. The results presented in the paper predict that reliable measurements should be possible during online testing.

Colossal dielectric behavior of semiconducting Sr2TiMnO6 ceramics

Manganitelike double perovskite Sr2TiMnO6 (STMO) ceramics fabricated from the powders synthesized via the solid-state reaction route, exhibited dielectric constants as high as similar to 10(5) in the low frequency range (100 Hz-10 kHz) at room temperature. The Maxwell-Wagner type of relaxation mechanism was found to be more appropriate to rationalize such high dielectric constant values akin to that observed in materials such as KxTiyNi(1-x-y)O and CaCu3Ti4O12. The dielectric measurements carried out on the samples with different thicknesses and electrode materials reflected the influence of extrinsic effects. The impedance studies (100 Hz-10 MHz) in the 180-300 K temperature range revealed the presence of two dielectric relaxations corresponding to the grain boundary and the electrode. The dielectric response of the grain boundary was found to be weakly dependent on the dc bias field (up to 11 V/cm). However, owing to the electrode polarization, the applied ac/dc field had significant effect on the low frequency dielectric response. At low temperatures (100-180 K), the dc conductivity of STMO followed a variable range hopping behavior. Above 180 K, it followed the Arrhenius behavior because of the thermally activated conduction process. The bulk conductivity relaxation owing to the localized hopping of charge carriers obeyed the typical universal dielectric response.

Colossal dielectric behavior of semiconducting $Sr_{2}TiMnO_{6}$ ceramics

Manganitelike double perovskite Sr2TiMnO6 (STMO) ceramics fabricated from the powders synthesized via the solid-state reaction route, exhibited dielectric constants as high as similar to 10(5) in the low frequency range (100 Hz-10 kHz) at room temperature. The Maxwell-Wagner type of relaxation mechanism was found to be more appropriate to rationalize such high dielectric constant values akin to that observed in materials such as KxTiyNi(1-x-y)O and CaCu3Ti4O12. The dielectric measurements carried out on the samples with different thicknesses and electrode materials reflected the influence of extrinsic effects. The impedance studies (100 Hz-10 MHz) in the 180-300 K temperature range revealed the presence of two dielectric relaxations corresponding to the grain boundary and the electrode. The dielectric response of the grain boundary was found to be weakly dependent on the dc bias field (up to 11 V/cm). However, owing to the electrode polarization, the applied ac/dc field had significant effect on the low frequency dielectric response. At low temperatures (100-180 K), the dc conductivity of STMO followed a variable range hopping behavior. Above 180 K, it followed the Arrhenius behavior because of the thermally activated conduction process. The bulk conductivity relaxation owing to the localized hopping of charge carriers obeyed the typical universal dielectric response.

Phase diagram and dielectric studies of binary organic materials

The phase equilibrium studies of organic system, involving resorcinol (R) and p-dimethylaminobenzaldehyde (DMAB), reveal the formation of a 1:1 molecular complex with two eutectics. The heat of mixing, entropy of fusion, roughness parameter, interfacial energy, and the excess thermodynamic functions were calculated based on enthalpy of fusion data determined via differential scanning calorimetric (DSC) method. X-ray powder diffraction studies confirm that the eutectics are not simple mechanical mixture of the components under investigation. The spectroscopic investigations (IR and NMR) suggest the occurrence of hydrogen bonding between the components forming the molecular complex. The dielectric measurements, carried out on hot-pressed addition compound (molecular complex), show higher dielectric constant at 320 K than that of individual components. The microstructural investigations of eutectic and addition compound indicate dendritic and faceted morphological features. (C) 2000 Elsevier Science B.V. All rights reserved.

Dielectric relaxations above room temperature in DMPU derived polyaniline film

Dielectric measurements carried out on drop casted from solution of emeraldine base form of polyaniline films in the temperature range 30-300 degrees C revealed occurrence of two maxima in the loss tangent as a function of temperature. The activation energies corresponding to these two relaxation processes were found to be similar to 0.5 eV and similar to 1.5 eV. The occurrence of one relaxation peak in the dispersion curve of the imaginary part of the electric modulus suggests the absence of microphase separation in the film. Thermogravimetric analysis and infrared spectroscopic measurements showed that the films retained its integrity up to 300 degrees C. The dielectric relaxation at higher temperatures with large activation energy of 1.5 eV is attributed to increase in the barrier potential due to decrease in the polymer conjugation as a result of wide amplitude motion of the chain segments well above the glass transition temperature. (c) 2012 Elsevier B.V. All rights reserved.

Glassy dielectric response in Tb2NiMnO6 double perovskite with similarities to a Griffiths phase

Results of frequency-dependent and temperature-dependent dielectric measurements performed on the double-perovskite Tb2NiMnO6 are presented. The real (epsilon(1)(f,T)) and imaginary (epsilon(2)(f,T)) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from the bulk, grain boundaries and the sample-electrode interfaces, respectively. The epsilon(1)(f,T) and epsilon(2)(f,T) are successfully simulated by a RC circuit model. The complex plane of impedance, Z'-Z `', is simulated using a series network with a resistor R and a constant phase element. Through the analysis of epsilon(f,T) using the modified Debye model, two different relaxation time regimes separated by a characteristic temperature, T*, are identified. The temperature variation of R and C corresponding to the bulk and the parameter alpha from modified Debye fit lend support to this hypothesis. Interestingly, the T* compares with the Griffiths temperature for this compound observed in magnetic measurements. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is markedly clear. We assume that the observed features have their origin in the polar nanoregions which originate from the inherent cationic defect structure of double perovskites. Copyright (C) EPLA, 2013

Magnetic frustration and dielectric relaxation in insulating Nd2NiMnO6 double perovskites

We have investigated structural, dielectric, and magnetic properties of polycrystalline double perovskite Nd2NiMnO6 compound. The compound crystallizes in monoclinic P2(1)/n symmetry and is partially B-site disordered depending on the synthesis conditions. It undergoes second-order ferromagnetic transition at 192K and shows glassy behaviour at low temperature. The glassy phase is due to anti-site disorder within the homogeneous sample. Temperature and frequency dependent dielectric measurements reveal colossal values of dielectric constant and is best interpreted using Maxwell-Wagner interfacial polarization model. Impedance spectroscopy has been used to analyse the intrinsic dielectric response. This enabled us to differentiate the conduction process at the grain and grain boundaries. Arrhenius behaviour is favoured at the grain boundary, while variable range hopping mechanism is considered most suitable within the grain region. dc conductivity measurements corroborate variable range hopping conduction. (C) 2015 AIP Publishing LLC.