Debye Peaks Research Articles

Investigation of Dielectric Properties of Quaternary Ceramic 0.47BNT-0.04BT-0.37PMN-0.18PT

Dielectric dispersion analysis has been carried out for the first time on a new quaternary ceramic [0.47(Bi0.5Na0.5)TiO3-0.04BaTiO3-0.31Pb(Mg1/3Nb2/3)O3-0.18PbTiO3] having a morphotropic phase boundary composition. The measurement of the dielectric parameters has been carried out in the frequency range of 200 Hz to 2 MHz and temperature range from 30 oC to 300 oC. The material showed high dielectric constant, low dielectric loss, negligible DC conductivity and high ferroelectric to paraelectric transition temperature. A clear Debye type relaxation was observed in the dielectric constant and dielectric loss data. An interesting feature of two Debye peaks has been noticed in dielectric loss versus frequency curves in the temperature range 125 oC to 175 oC. These peaks shift towards higher frequencies when temperature is increased. The extracted relaxation times of the two peaks are three orders of magnitude different and have been found to follow the Arrhenius law with significantly different activation energies.

Thermoelastic Damping in Partially Covered Bilayer Microbeam Resonators with Two-Dimensional Heat Conduction

Thermoelastic damping (TED) has been proved as an intrinsic mechanism of energy dissipation in the microelectromechanical systems (MEMS) resonators. However, the previous TED models developed for the fully covered bilayer beam resonators cannot be used for the partially covered cases. This paper firstly derives an analytical TED model for partially covered bilayer microbeams. The bilayer beam performs small-amplitude vibration in pure bending mode, and the mode shape is achieved from the dynamic of Euler-Bernoulli beam. To obtain the coupled temperature field, Green's functions are utilized to solve the heat conduction along thickness and length directions within the framework of Fourier's law. The expression for TED is derived in the form of an infinite series. The present TED model can reduce to that of a fully covered bilayer beam, and matches well with the finite element method (FEM). The behaviors of TED spectrum are investigated comprehensively. Two comparable Debye peaks are noticed at approximately two corresponding critical frequencies. The partial coating greatly reduces the peak values at high critical frequency, but causes an additional TED peak at low critical frequency. The TED peaks of the coating slightly increase as the length increases. The effects of the length and position of the metal coating on the TED at the fundamental frequency are significant. To reduce TED, the metal coating should be located away from the substrate clamped end. This paper provides a developing methodology for controlling TED.

Excess wing physics and nearly constant loss in glasses

Excess wings and nearly constant loss are almost universal nonequilibrium phenomena in glass formers. Both lack an accepted theoretical foundation. A model-free and unified theoretical description for these phenomena is presented that encompasses also fast -processes, emergent Debye peaks, and the relaxation strength of the boson peak. The theory is model-free in the same way as the classical Debye relaxation equation for orientational polarisation. It is based on generalizing time flow from translation semigroups to composite time translation-convolution semigroups. Composite translation-convolution fits have less parameters than traditional fits. They need only one dynamic scaling exponent, while four are needed in Havriliak–Negami fits. For glycerol the single dynamic exponent in the translation-convolution fit is found to be temperature-independent.

Impact of Gd and Cu substitution on dielectric and magnetic properties of MnFeO3 multiferroic materials

Gadolinium (Gd) and copper (Cu) substituted MnFeO3 nanoparticles were synthesized via sol gel auto-combustion route. In imaginary electric modulus Debye peaks occurred which indicated the phenomenon of relaxation in the given frequency range. Cole-Cole plots were taken to investigate the contribution of grain and grain boundaries. The grain boundary resistance increased as compared to grain resistance with the incorporation of Gd and Cu. Magnetization and remanence were observed to decrease while coercivity (Hc) increased with Gd-Cu substitution. The phenomenon of super exchange interaction takes place between cations which reside on tetrahedral and octahedral sites. The magnetic ordering and spin canting were distorted with the substitution of Gd and Cu which leads to decrease in magnetic properties. The value of coercivity was raised upto 1992 Oe which proposed that synthesized multiferroics are useful in the fabrication of perpendicular recording media.

Statistical Mechanics Treatment of the Broadened Snoek Relaxation Peak in Ternary Niobium⁻Vanadium⁻Oxygen Alloys.

The Snoek relaxation profiles for ternary Niobium–Vanadium–Oxygen systems were analyzed by an embedded-cell model of statistical mechanics treatment. The relaxation characteristic and broadening mechanism were systematically discussed and some conflicting interpretations in the early research were clarified. The complicated Snoek spectrums of the Nb–V–O system can be resolved into a series of effective elementary Debye peaks, which result from the transitions of interstitial oxygen atoms between adjacent octahedral sites. The relaxation parameters of each elementary peak can be determined by element species and atomic arrangements within the corresponding embedded octahedron. The Snoek relaxation characteristic in Nb–V–O systems mainly depends on the sites distributions and the transitions status of the interstitial oxygen atoms, which are controlled by the site-dependence energies and the transition probabilities, respectively.

The origin of the Debye relaxation in liquid water and fitting the high frequency excess response.

We critically review the literature on the Debye absorption peak of liquid water and the excess response found on the high frequency side of the Debye peak. We find a lack of agreement on the microscopic phenomena underlying both of these features. To better understand the molecular origin of Debye peak we ran large scale molecular dynamics simulations and performed several different distance-dependent decompositions of the low frequency dielectric spectra, finding that it involves processes that take place on scales of 1.5-2.0 nm. We also calculated the k-dependence of the Debye relaxation, finding it to be highly dispersive. These findings are inconsistent with models that relate Debye relaxation to local processes such as the rotation/translation of molecules after H-bond breaking. We introduce the spectrumfitter Python package for fitting dielectric spectra and analyze different ways of fitting the high frequency excess, such as including one or two additional Debye peaks. We propose using the generalized Lydanne-Sachs-Teller (gLST) equation as a way of testing the physicality of model dielectric functions. Our attempts at fitting the experimental spectrum using the gLST relation as a constraint indicate that the traditional way of fitting the excess response with secondary and tertiary Debye relaxations is problematic. All of our work is consistent with the recent theory of Popov et al. (2016) that Debye relaxation is due to the migration of Bjerrum-like defects in the hydrogen bond network. Under this theory, the mechanism of Debye relaxation in liquid water is similar to the mechanism in ice, but the heterogeneity and power-law dynamics of the H-bond network in water results in excess response on the high frequency side of the peak.

Annealed SnO2 thin films: Structural, electrical and their magnetic properties

SnO2 thin films of ~150nm thicknesses were deposited on quartz substrate by pulse laser deposition technique and annealed at 600–900°C for 1h with a variation of 100°C per sample. The X-ray diffraction patterns show that as deposited SnO2 thin film was completely amorphous while annealed SnO2 thin films were randomly oriented, polycrystalline in nature and correspond to the rutile phase. The average crystallite size estimated using Scherrer and Williamson–Hall equations was found to increase with annealing temperature. In addition to the three fundamental Raman peaks at 473cm−1, 627cm−1 and 766cm−1 corresponding to the tetragonal rutile phase of SnO2, two IR active Raman bands and one Raman forbidden mode were also observed at 500cm−1, 690cm−1 and 544cm−1 respectively. The dc resistivity measurements in the temperature range of 297–400K show semiconducting behavior of all the annealed thin films. Room temperature dielectric properties of all the samples show dispersion which is explained in the light of Koop's theory based on Maxwell–Wagner two layer models. The dielectric parameters: real part of dielectric constant, dielectric loss and ac conductivity show their maximum value for SnO2 film sample annealed at 600°C. The dielectric loss shows anomalous behavior and exhibits relaxation peaks (Debye peaks) at lower and middle frequencies. Complex impedance plots (Nyquist plots) for annealed SnO2 thin films show two well-resolved semicircles corresponding to two different electrical transport mechanisms which stand for grain and grain boundary. It is observed that the contribution of grains in the conduction process starts dominating over the grain boundary with the increase in annealing temperature. From a magnetic hysteresis loop, it is clear that all the single phase SnO2 thin films annealed at different temperatures are ferromagnetic at room temperature and the value of saturation magnetization shows its maximum for the film annealed at 600°C.

Synchrotron X-ray diffraction to detect glass or ice formation in the vitrified bovine cumulus-oocyte complexes and morulae.

Vitrification of bovine cumulus-oocyte complexes (COCs) is not as successful as bovine embryos, due to oocyte's complex structure and chilling sensitivity. Synchrotron X-ray diffraction (SXRD), a powerful method to study crystal structure and phase changes, was used to detect the glass or ice formation in water, tissue culture medium (TCM)-199, vitrification solution 2 (VS2), and vitrified bovine COCs and morulae. Data revealed Debye's rings and peaks associated with the hexagonal ice crystals at 3.897, 3.635, 3.427, 2.610, 2.241, 1.912 and 1.878 Å in both water and TCM-199, whereas VS2 showed amorphous (glassy) appearance, at 102K (−171°C). An additional peak of sodium phosphate monobasic hydrate (NaH2PO4.H2O) crystals was observed at 2.064 Å in TCM-199 only. All ice and NaH2PO4.H2O peaks were detected in the non-vitrified (control) and vitrified COCs, except two ice peaks (3.145 and 2.655 Å) were absent in the vitrified COCs. The intensities of majority of ice peaks did not differ between the non-vitrified and vitrified COCs. The non-vitrified bovine morulae in TCM-199 demonstrated all ice- and NaH2PO4.H2O-associated Debye's rings and peaks, found in TCM-199 alone. There was no Debye's ring present in the vitrified morulae. In conclusion, SXRD is a powerful method to confirm the vitrifiability of a solution and to detect the glass or ice formation in vitrified cells and tissues. The vitrified bovine COCs exhibited the hexagonal ice crystals instead of glass formation whereas the bovine morulae underwent a typical vitrification.

Quasi-Solid Semi-Interpenetrating Polymer Networks as Electrolytes: Part III. Probing the Mechanism of Ionic Charge Transport Employing Temperature-Step Electrochemical Impedance Spectroscopy

The correlated ion-transport mechanism and its dependence on microscopic phase separation for a new class of quasi-solid semi-IPN electrolytes is probed in considerable detail using temperature-step electrochemical impedance spectroscopy. The response of electrolyte matrices under alternating current perturbation is comprehensively analyzed using a simulated model fit to extract pertinent information relevant to the phase composition and homogeneity, contribution of each phase, interfacial charge-transfer resistance, phase entanglement zones, bulk relaxation time for ionic hopping mechanisms, coupled segmental motions, rate of site reorganization that dictates successful hopping events, and estimates of ionic transport numbers. The normalized complex plane Nyquist plots (ρ′ versus ρ″) show two well-defined regions for bulk (in mid- and high-frequency regions) and electrode–electrolyte interfacial impedance (in low-frequency regions). Rigorous analysis indicates the presence of three microscopic phases in the matrix bulk (pure poly(ethylene oxide)–polyurethane (PEO-PU), pure poly(ethylene glycol) dimethyl ether (PEGDME), and PEO-PU/PEGDME mixed phase) along with the charge-transfer resistance (Rct) which contribute to the bulk resistance. Spectroscopic plots of complex impedance against frequency (Z″ versus log f) depict Debye peaks, providing an estimate of the bulk relaxation time (τpeak). Profiles depicting the real component of conductivity (σ′(ω)) as a function of frequency (log f) follow a modified universal power law where the simulated fit results reveal vital information on the site relaxation rates, cumulative favorability for successful hopping events, and predominant charge carrier type. The behavior of the dielectric contributions provides insights into the various ion polarization processes dominant in the high-, mid-, and low-frequency windows of the sweep. These trends were further correlated with our prior evaluation of the physico-chemical properties of the semi-IPN matrices to propose a rational physical model for these complex systems.

Dynamics of glass-forming liquids. XVII. Dielectric relaxation and intermolecular association in a series of isomeric octyl alcohols

It is well established that many mono-hydroxy alcohols show an extra relaxation process of the Debye type in addition to the signatures of primary and secondary structural relaxations, which is observed only in dielectric spectroscopy and related techniques. In order to gain further insight into the nature of this Debye peak, we study the linear and nonlinear dielectric behavior of a series of isomeric octyl alcohols and of mixtures of n-propanol with one of the octanols. These samples display systematic variations of the Debye peak intensity and concomitant changes in the Kirkwood correlation factor gK from 0.1 to 4, indicative of different equilibrium constants, K(c∕r), that characterize the populations of non-polar ring and polar open chain structures. For cases where K(c∕r) is not too far from unity, we find that a high electric field shifts K(c∕r) towards more chains, and that the accompanying change in the end-to-end vector of hydrogen-bond connected structures occurs on the Debye time scale. The results suggest that gK is correlated with the spectral separation of the Debye and primary structural peaks, as both features depend on steric hindrance of chain flexibility or bond rotation barriers and on average chain lengths. Based on the complex dynamics of supercooled mono-hydroxy alcohols with three relaxation peaks that cover many orders of magnitude in frequency, it is argued that a frequency dependent gK may be required for assessing the average orientational correlations within hydrogen-bonded structures correctly.

Anelastic Effects on Martensitic Carbon Steels during First Stage of Tempering

The evolution of martensitic carbon steel during low temperature tempering was studied using internal friction. The steel containing 0.71wt.% carbon was heated at 1093K for 5min and then rapidly cooled into water (quenched), and tempered for 10 min at 340, 380, 420 and 460K. Additionally, other samples were tempered at 380K for 1 and 20 hours. Internal friction was measured by using a forced vibration pendulum, in a temperature range from 300 to 600K, with deformation amplitude 3 x 10-6 and temperature rate of 0.8 K/min. The internal friction spectrum is decomposed into three Debye peaks: P1 at 380K, P2 at 420K and P3 at 480K, for 3 Hz. P1 is attributed to the epsilon carbide precipitation. P2 and P3 are associated to the dislocation relaxation process. P2 appears when dislocations are pinning with epsilon carbide and P3 appears when dislocations are pinning with cementite carbide.

Hydrogen-Induced Mechanical Losses in Oxygen-Free Copper

Two oxygen-free copper grades with purity of 99.99 % were studied by means of free decay inverted torsion pendulum at the temperature range of 90 – 300 K and frequencies of 0.5 – 2 Hz. One copper grade was oxygen free electrolytically refined copper with oxygen content of 1.2 wt. ppm. The other one was oxygen-free phosphorous-alloyed grade with oxygen content less than 5 wt. ppm and phosphorous content of 30 – 70 wt. ppm. Electrochemical hydrogen charging induces a complex internal friction peak in the studied copper grades. The observed internal friction peak has a relaxation origin with apparent activation enthalpy and pre-exponential factor for the oxygen-free grade of 0.276 ± 0.002 eV and 10-11.59 ± 0.08 s, respectively. The internal friction peak can be fitted by three broadened Debye peaks (P1, P2 and P3) with activation enthalpies and pre-exponential factors of 0.248 ± 0.003 eV and 10-11.4 ± 0.4 s; 0.297 ± 0.004 eV and 10-11.8 ± 0.2 s; 0.36 ± 0.04 eV and 10-12.7 ± 1.4 s, respectively. Phosphorous doping markedly reduces the height of the observed peak. It was also shown that prior deformation by tension suppresses high-temperature components of the complex internal friction peak. Mechanism of relaxation is presumably caused by interaction of H – H pairs (low-temperature component, peak P1), interaction of hydrogen atoms with dislocations (P2) and interaction of hydrogen with impurities (high-temperature component, peak P3). Absorption of hydrogen in the studied copper grades during electrochemical hydrogen charging was confirmed by the thermal desorption method.

Diffusion Phenomena of the Oxygen and Nitrogen in Niobium by Mechanical Spectroscopy

The short-range diffusion phenomenon (Snoek Effect) was investigated by mechanical spectroscopy measurements between 300 K and 650 K, in a polycrystalline niobium sample, containing oxygen and nitrogen, using a torsion pendulum. Experimental spectra of anelastic relaxation were obtained under three conditions: as-received sample; annealed sample and subsequently annealed in an oxygen atmosphere for three hours at 1170 K in partial pressure of 5x10-5mbar. The experimental spectra obtained were decomposed in elementary Debye peaks and the anelastic relaxation processes were identified. With anelastic relaxation parameters and the lattice parameters, the interstitial diffusion coefficients of the oxygen and nitrogen in niobium were calculated for each kind of preferential occupation (octahedral and tetrahedral). The results were compared with the literature data, and confirmed that the best adjustment is for the preferential occupation octahedral model for low concentrations of interstitial solutes, but at higher concentration of oxygen were observed deviations of experimental data for the interstitial diffusion coefficients of oxygen in niobium when compared with the literature data, this could be related to the possible occurrence of a double occupation of interstitial sites in the niobium lattice by oxygen interstitials.

Sharp low frequency dissipative effects in tetragonal BaTiO3 ceramics

Mechanical anomalies (damping peaks sharper than Debye peaks, in contrast to a broad relaxation peak) were observed in tetragonal barium titanate ceramic via broadband viscoelastic spectroscopy at low frequencies (<10 Hz) at ambient temperature after aging at 90 °C for 15 h. The sharp peaks disappear after aging above the Curie point (150 °C for 10 h). Mechanical anomalies are tentatively attributed to negative stiffness heterogeneity, the mechanism of which is proposed based upon the theory of symmetry-conforming short-range order property of point defects.

Impedance studies on high energy Li 3+ irradiated PZT thin films

The ferroelectric Pb(Zr 0.48Ti 0.52)O 3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiated films, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25 eV of unirradiated film to 1.62 eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss.

Glass Transitions in Viscous Monohydroxy Alcohols: Calorimetry Versus Dielectric Relaxation

An extensive comparison of the calorimetric and dielectric measurements of the glass transitions in both monohydroxy alcohols and other molecular liquids is presented, with only these alcohols displaying an additional pronounced dielectric Debye peaks. It is found that the calorimetric T g’s of the non-Debye liquids with moderate cooling and heating rates (±20 K · min−1, for example) are slightly higher than the kinetic ones which are determined as the temperatures at which the relaxation time is 100 s. As the difference does not exceed 3 K, this relation of calorimetric and kinetic T g’s is used as ‘standard.’ Two kinetic glass transitions from the dielectric relaxation of Debye type monohydroxy alcohols are identified, and it is found that the Debye process is not the signature of the glass transition.

Internal friction of Niobium–Titanium–Oxygen alloys

The compositional and temperature dependence of the anelastic relaxation behavior in Nb–Ti–O alloys have been investigated. Using a fitting method, the complicated relaxation spectra were resolved into several elementary Debye peaks, which corresponded to the reorientation transitions of O atoms at different octahedral interstitial sites. The number of the peaks depended upon the Ti concentration. The calculation results of the site energies show that the interstitial oxygen atoms preferentially occupy the octahedral interstitial site, which has nearest-neighbor Ti substitutional atoms. Therefore, substitutional Ti solutes will markedly influence the Snoek relaxation behavior in Nb-Ti-O ternary system, even if the concentration of Ti is rather low.

Natural mechanism of the broadened Snoek relaxation profile in ternary body-centered-cubic alloys

The natural mechanism of the broadened Snoek relaxation peak in the ternary bcc alloy system has been investigated by an embedded-cell model of statistical mechanical treatment. In this method, interstitial sites of different geometries (octahedral, tetrahedral, etc.) in bcc crystals are considered and further distinguished by element species and atomic arrangements within their first shell of the neighbors. Following these preconditions, the interstitial site occupancies, the spatial configurations, and the transition probabilities of the interstitial atoms are concretely calculated for the ternary bcc alloy system, and all possible elementary relaxation processes contributing to the broadened Snoek peak are physically described with the determined activation energy and peak temperature for each elementary process. Using this approach for Snoek peak deconvolution, the broadened Snoek peak of the ternary bcc alloy can be resolved into several elementary Debye peaks, which correspond to the concrete relaxation mechanism. In the present study, this method is successfully applied to analyze the natural mechanism of experimentally observed Snoek relaxation in Nb-Ti-O systems.

Determination of the oxygen and nitrogen interstitial diffusion coeficient in niobium by mechanical spectroscopy

Mechanical spectroscopy measurements have been extensively used in the last decades to obtain information about many aspects of the behavior of solutes in metallic materials. Metals of body-centered cubic lattice that contain heavy interstitial elements (oxygen, nitrogen and carbon) in solid solution, present anelastic relaxation peaks when submitted to cyclic tensions, due to process know stress-induced ordering. Internal friction and frequency as a function of temperature were performed between 300 K and 650 K in a polycrystalline sample of Nb, for three distinct conditions, using a torsion pendulum inverted Kê-type operating in a frequency oscillation between 1Hz and 10 Hz range, with a heating rate of 1 K/min and pressure lower than 2 x 10-5 mbar. The experimental spectra obtained for each condition of the sample, were decomposed by the successive subtraction method in elementary Debye peaks. The following metal-interstitial interactions were identified: Nb-O and Nb-N for all conditions of the sample. From the anelastic relaxation parameters obtained (relaxation strength, peak temperature, activation energy and relaxation time) and lattice parameter (obtained from x ray diffraction), the determination of the oxygen and nitrogen interstitial diffusion coefficient in Nb was possible, for each condition of the sample.

Interstitial Diffusion of Oxygen in Tantalum Obtained by Anelastic Relaxation Measurements

Anelastic relaxation measurements have been used in order to obtain information about several aspects of the behavior of solutes in metals, for example, matrix-solute interaction, interstitial diffusion, etc. The diffusion coefficient for interstitial solutes in body centered-cubic metals is accurately determined by anelastic relaxation measurements. The kind of preferential occupation of the interstitial solutes in body centered-cubic metals, such as oxygen and nitrogen in tantalum, is still controversial. Internal friction and frequency measurements as a function of temperature in tantalum sample were performed using a torsion pendulum operating in a frequency oscillation in the hertz bandwidth. These results presented the following phenomenon: the intensity of the internal friction peak decreased between the first run and the other runs. These results were decomposed, by the successive subtraction method, in elementary Debye peaks, for determination of characteristic anelastic relaxation parameters (relaxation strength, peak temperature, activation energy and relaxation time). Interstitial diffusion coefficients for oxygen in tantalum were determined, for different intensities of internal friction peaks, and when compared with literature, these results introduced a better adjustment for the tetrahedral preferential occupation sites of oxygen in tantalum.