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A simulator of lunar permafrost at 100 K exhibits a dielectric relaxation centered at approximately 300 hertz. If permafrost exists in the moon between 100 and 213 K, it should present a relaxation peak at approximately 300 hertz. For temperatures up to 263 K it may go up to 20 kilohertz.
The dielectric response of permafrost at 100 K and vacuums of around 10 ntorr is analyzed, varying its percent ice content from 1 to 18.6. The distributions obtained correspond to dielectric relaxations of the Cole-Cole type, with maximum losses occurring in the 30- to 600-Hz frequency range. The logarithms of such maxima depend linearly on the permafrost ice content, two regions of linear variation being defined above and below 3.6% ice content. Such relations point out the feasibility of determining ice content in permafrost by electromagnetic means.
An oriented piezoelectric film incorporated in the insulator region of a silicon insulated-gate field-effect transistor (FET) results in a sensitive high-frequency strain transducer. Theory governing the transducer properties of the piezoelectric insulator FET transducer is presented. Equations are developed which relate the drain current of the device to induced polarizations of the piezoelectric layer. The highest frequency of surface strains to which the FET transducer can respond is determined by the FET frequency response - ultimately by the channel transit time. This frequency can extend to the GHz range. The low-frequency response to applied strain is determined by the dielectric relaxation frequency of the piezoelectric layer.
Measurements made on several doped-silicon detectors are reported. Topics discussed include: Si:Sb detector, the effects of detector bias on dielectric relaxation; characterization of spontaneous noise and gamma-induced spikes and their circumvention; and the time response of two detectors to step changes in the background photon flux density. Several potential system programs are indicated.
Recent measurements on the dielectric constants of soil-water mixtures show the existence of two frequency regions in which the dielectric behavior of these mixtures was quite different. At the frequencies of 1.4 GHz to 5 GHz, there were strong evidences that the variations of the dielectric (epsilon) with water content (W) depended on soil type. While the real part of epsilon for sandy soils rose rapidly with the increase in W, epsilon for the high-clay content soils rose only slowly with W. As a consequence, epsilon was generally higher for the sandy soils than for the high-clay content soils at a given W. On the other hand, most of the measurements at frequencies 1 GHz indicated the increase of epsilon with W independent of soil types. At a given W, epsilon' (sandy soil) approximately equals epsilon (high-clay content soil) within the precision of the measurements. These observational features can be satisfactorily interpreted in terms of a simple dielectric relaxation model, with an appropriate choice of the mean relaxation frequency f(m) and the range of the activation energy (beta). It was found that smaller f(m) and larger beta were required for the high-clay content soils than the sandy soils in order to be consistent with the measured data.
An experimental study of the transient behavior of Ge:Be and Ge:Zn photoconductors to changes in photon flux rates has been performed under the low background flux conditions (10 to the 8th photon/s) typical of astronomy and astrophysics applications. A characteristic transient behavior with time constants ranging from 0.1 to greater than 5 s has been observed in both materials when the shallow levels are very closely compensated. The detector response consists of both a fast and a slow component. The amplitude of the slow component can be up to 10 times greater than the initial fast component. It has been established that this phenomenon cannot be explained by current models of carrier sweep-out or dielectric relaxation. The transient behavior has been characterized as a function of temperature, electric field, photoconductive gain and material parameters.
The performance as a THz-frequency modulator of a small-area Schottky diode mounted in a corner-cube antenna is evaluated, including the effects of carrier inertia and dielectric relaxation. Calculations are performed for a 1.4-micron diameter diode operating at a carrier frequency of 2.252 THz and a modulation frequency of 8 GHz. The phase modulation is found to completely dominate the amplitude modulation. The performance is shown to be degraded well below the plasma frequency in the undepleted epilayer due to the presence of a second resonance caused by the interaction of the barrier capacitance and the effective inductance due to carrier inertia. An increase in epilayer doping (reducing the diode radius) may improve the single-sideband conversion efficiency by about 20 dB.
A capacitance/dielectric sensor was designed, constructed, and used to measure in real time the in-situ water concentration in a desiccant water bed. Measurements were carried out with two experimental setups: (1) passing nitrogen through a humidity generator and allowing the gas stream to become saturated at a measured temperature and pressure, and (2) injecting water via a syringe pump into a nitrogen stream. Both water vapor generating devices were attached to a downstream vertically-mounted water capture bed filled with 19.5 g of Moisture Gone desiccant. The sensor consisted of two electrodes: (1) a 1/8" dia stainless steel rod placed in the middle of the bed and (2) the outer shell of the stainless steel bed concentric with the rod. All phases of the water capture process (background, heating, absorption, desorption, and cooling) were monitored with capacitance. The measured capacitance was found to vary linearly with the water content in the bed at frequencies above 100 kHz indicating dipolar motion dominated the signal; below this frequency, ionic motion caused nonlinearities in the water concentration/capacitance relationship. The desiccant exhibited a dielectric relaxation whose activation energy was lowered upon addition of water indicating either a less hindered rotational motion or crystal reorientation.
This technical memorandum presents the data and results from a series of tests performed on AVCOAT, charred AVCOAT, and different Shuttle Thermal Protection System (TPS) tile coatings to determine their electrical properties as a function of temperature and frequency. Initially, the samples were assumed to be insulators and the complex permittivities were measured from data collected by sandwiching each sample between two conductors to form a sandwich. However, the AVCOAT sample data showed that the material becomes conductive as it begins to char. To get an accurate conductivity reading on these charred samples, a four-point resistance probe was used to collect data. Overall, this testing showed that the virgin AVCOAT starts out as a material that is a good insulator but transitions to one with a conductivity on the order of 1860 S/m as it chars. The deeper layers of AVCOAT (un-charred) all exhibited a temperature and frequency dependence that is possibly indicative of a dielectric relaxation in the material. As the sample temperatures were increased, a knee appears in the real permittivity data sets below 1 kHz. Both the real permittivity and resistivity drop up to several orders of magnitude yet show that the material remains an insulator. The Shuttle High Temperature Reusable Surface Insulation (HRSI) tile coatings studied included Reac- tion Cured Glass (RCG), Aluminum Enhanced Thermal Barrier (AETB), and Toughened Unipiece Fibrous Insulation (TUFI). The purely glass fiber parts of the tile were removed leaving only the outer layers con- taining just the coating. The data collected shows that the RCG, AETB, and outermost layer of the TUFI have similar electrical properties. The real permittivity plots show that there appears to be a relaxation that shows up at frequencies below 1 kHz. The relaxation frequency increases with increasing temperature. Also, the real permittivity increases up to about a factor of four between room temperature and 650K. Likewise, the resistivity (related to the imaginary permittivity) decreases up to five orders of magnitude over the same temperature interval, but still remains an insulator. This data was collected to support a NASA Engineering and Safety Center (NESC) assessment team investigating the source of thermocouple anomalies in both Shuttle TPS material and AVCOAT used for on the Orion spacecraft for Exploration Flight Test 1 (EFT-1). The details of their findings will be documented in a separate report with this document serving as a reference.
We use broad-band dielectric spectroscopy (BDS) and small-angle X-ray scattering (SAXS) to investigate the impact of architectural asymmetry in the miktoarm star copolymer on the dielectric polymer relaxations. The miktoarm copolymers studied contain one or two polystyrene (PS) chains of constant molecular weight and two identical poly(cis-1,4-isoprene) (PI) chains with varied molecular weights. Using the chains in the PI block as dielectric probes, we find that the architecturally asymmetric miktoarm star copolymer systems (PSPI 2 ) feature distributions in chain relaxation times and dielectric relaxation strengths that are not dependent on molecular weight or morphology, in stark contrast to the effects of morphological confinement observed for symmetric diblock systems (PS-b-PI or PS 2 PI 2 ). Along with evidence from the SAXS measurements regarding phase separation, these results are attributed to influences from chain stretching within the framework of the Gaussian chain model for block copolymer systems. As such, the molecular architecture in block copolymers happens to be a versatile handle to control polymer chain dynamics and, ultimately, the macroscopic physicochemical properties in architecturally complex polymers.
Dielectric spectroscopy is extremely powerful to study molecular dynamics, because of the very broad frequency range. Often multiple processes superimpose resulting in spectra that expand over several orders of magnitude, with some of the contributions partially hidden. For illustration, we selected two examples, (i) normal mode of high molar mass polymers partially hidden by conductivity and polarization and (ii) contour length fluctuations partially hidden by reptation using the well-studied polyisoprene melts as example. The intuitive approach to describe experimental spectra and to extract relaxation times is the addition of two or more model functions. Here, we use the empirical Havriliak-Negami function to illustrate the ambiguity of the extracted relaxation time, despite an excellent agreement of the fit with experimental data. We show that there are an infinite number of solutions for which a perfect description of experimental data can be achieved. However, a simple mathematical relationship indicates uniqueness of the pairs of the relaxation strength and relaxation time. Sacrificing the absolute value of the relaxation time enables to find the temperature dependence of the parameters with a high accuracy. For the specific cases studied here, the time temperature superposition (TTS) is very useful to confirm the principle. However, the derivation is not based on a specific temperature dependence, hence, independent from the TTS. We compare new and traditional approaches and find the same trend for the temperature dependence. The important advantage of the new technology is the knowledge of the accuracy of the relaxation times. Relaxation times determined from data for which the peak is clearly visible are the same within the experimental accuracy for traditional and new technology. However, for data where a dominant process hides the peak, substantial deviations can be observed. Finally, we conclude that the new approach is particularly helpful for cases in which relaxation times need to be determined without having access to the associated peak position.
Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO 3 -Bi(Mg 0.5 Ti 0.5 )O 3 relax or dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High resolution, synchrotron X-ray diffraction indicated a globally cubic structure ($Pm$$\overline{3}$$m$), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along < 100 > and < 110 > zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2–5 nm. Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.
Solid materials with a high dielectric constant have a wide range of applications in the energy storage field. In this research, an imidazolium-based zwitterion is designed, synthesized, and confirmed to have a plastic crystal phase based on the following experimental and computational evidence: (i) the presence of long-range order with weak intermolecular forces and competing attractive-repulsive interactions along different crystallographic directions; (ii) the observation of more than one endotherm on heating including a solid-solid phase transition at T s-s = −26 °C and melting of the plastic crystal at T m = 72°C; (iii) a low entropy of fusion at melting (2.1 JK −1 mol −1 ); (iv) a strongly anisotropic morphology; (v) relatively fast dynamics originating from short-range degrees of freedom. Furthermore, it exhibits a very high dielectric constant in the plastic crystal solid state (147 at −10°C and 103 at 70°C) due to the rotational degrees of freedom of plastic crystals that arise from weak net intermolecular interactions of zwitterions due to only having two carbons between the anion and cation. This material conveniently remains in the plastic crystal phase within 50 K of ambient temperature. This discovery opens new opportunities in the search for solid-state high dielectric constant materials.
Abstract The interaction of condensed phase systems with external electric fields is of major importance in a myriad of processes in nature and technology, ranging from the field-directed motion of cells (galvanotaxis), to geochemistry and the formation of ice phases on planets, to field-directed chemical catalysis and energy storage and conversion systems including supercapacitors, batteries and solar cells. Molecular simulation in the presence of electric fields would give important atomistic insight into these processes but applications of the most accurate methods such as ab-initio molecular dynamics (AIMD) are limited in scope by their computational expense. Here we introduce Perturbed Neural Network Potential Molecular Dynamics (PNNP MD) to push back the accessible time and length scales of such simulations. We demonstrate that important dielectric properties of liquid water including the field-induced relaxation dynamics, the dielectric constant and the field-dependent IR spectrum can be machine learned up to surprisingly high field strengths of about 0.2 V Å −1 without loss in accuracy when compared to ab-initio molecular dynamics. This is remarkable because, in contrast to most previous approaches, the two neural networks on which PNNP MD is based are exclusively trained on molecular configurations sampled from zero-field MD simulations, demonstrating that the networks not only interpolate but also reliably extrapolate the field response. PNNP MD is based on rigorous theory yet it is simple, general, modular, and systematically improvable allowing us to obtain atomistic insight into the interaction of a wide range of condensed phase systems with external electric fields.
Description of the dielectric constants, losses, and ac-conductivities of lunar samples 15065,27, 15459,62, 15555,88, 15415,57, 60015,29, 60315,34, 61016,34, and 62235,17 as measured over a range of frequencies from 100 Hz to 10 MHz and temperatures from 77 to 473 K by two-terminal capacitance substitution methods. The dielectric spectra of lunar gabbroic basalts are typified by the dielectric behavior of samples 15065 and 15555, showing complex relaxation processes which are both frequency- and temperature-dependent. Such feldspar-rich crystalline lunar basalts like samples 15459, 62235, and 60015 showed essentially the same dielectric relaxation mechanisms which are also a function of both frequency and temperature with a very broad relaxation frequency distribution. Highly-brecciated lunar sample, 60315, exhibits rather an unusual dielectric behavior which is dependent upon on field-strength.
Dielectric constants, dipole moments, relaxation times, conduction phenomena, insulating films, breakdown, materials, and applications of dielectrics - annotated bibliography
Poly(dimethylsiloxane) (PDMS)-based bottlebrush polymers, PDMS-g-PDMS, have been synthesized by anionic polymerization in combination with a condensation-based grafting reaction. Bottlebrush polymers show intriguing features, e.g., extremely low viscosities. Hereby, studies of their dynamics are rare. Therefore, we focus on the segmental relaxation by broadband dielectric spectroscopy. An increasing cross-sectional radius proportional to the increasing side chain length has been observed by small-angle neutron scattering over three samples. Here, a comparison of the segmental relaxation times of the bottlebrushes with the respective linear chains reveals slower dynamics in the former. For longer chains, this effect vanishes.
Bottlebrushes are an interesting class of polymers which shows intriguing material properties often associated with dynamics. While dynamical phenomena in linear polymers are well understood and existing theories can describe them in a good way, bottlebrush dynamics have only rarely been investigated. Therefore, we performed dielectric spectroscopy and quasi-elastic neutron scattering to study the dynamics of polydimethylsiloxane-based bottlebrush polymers, PDMS-g-PDMS focusing mostly on the segmental dynamics of the side chains. Comparing the relaxation times of the α – relaxation, tracked with dielectric spectroscopy, of bottlebrush polymers with those of their respective linear side chains show a slowing down once the side chains are attached to the backbone. This effect diminishes and finally vanishes with increasing side chain length. The time and length scale, offered by quasi-elastic neutron scattering, fits for the segmental dynamics together with faster processes. The Q -dependence of the segmental relaxation times allows to classify bottlebrush polymers as heterogenous including a non-Gaussian character. For such a dynamical system, the mean square displacement needs to be separated into single processes before an overall mean square displacement can be generated by applying the time temperature superposition principle.