Temperature Dependence Of Dielectric Loss Research Articles

Two-level system loss: Significant not only at millikelvin

Tow-level system (TLS) loss in amorphous dielectric materials has been intensively studied at millikelvin temperatures due to its impact on superconducting qubit devices and incoherent detectors. However, the significance of TLS loss in superconducting transmission lines at liquid helium temperatures remains unclear. This study investigates TLS loss in amorphous SiO2 at liquid helium temperatures (about 4 K) within a frequency range of 130–170 GHz, using niobium microstrip and coplanar waveguide resonators. Our results demonstrate notable power and temperature dependence of dielectric loss, with the dielectric loss and quasiparticle loss exchanging dominance at around 4 K. These findings are consistent with TLS models and provide crucial insight for the design of superconducting devices operating at liquid helium temperatures.

Temperature dependent dielectric studies of pure and Sr doped Pr2NiMnO6

The physical properties of Sr doped Pr2NiMnO6 have been discussed. The Samples of Pr2-xSrxNiMnO6 (x = 0.0, 0.2, 0.4) have been synthesized via Solid State Reaction. The X-Ray diffraction and Scanning Electron Microscopy characterizations were applied to examine the structure and surface morphology. Observed XRD patterns reveal the structure to be monoclinic with P21/n space group. Increase in the Sr doping resulted in the reduction in the particle size and crystallite size. Raman peak corresponding to the wave number 515 cm−1 represents the asymmetric mode and the other one at 655 cm−1 represents symmetric mode of the NiO6/MnO6 octahedra. The frequency and temperature dependent dielectric studies on samples of Pr2-xSrxNiMnO6 (x = 0.0, 0.2, 0.4) suggest the decrease in dielectric constant with the increase in Sr doping. The appearance of relaxation peak has been also observed in the temperature dependent dielectric loss plots. Furthermore, the ac conductivity reduction has been seen with the increase in Sr doping.

Analysis of dielectric losses in chromespinelide samples from the ophiolite complexes of the Urals

Relevance is determined by the need to search for scientifically based criteria for the identification of chromite mineralization. The purpose of this work is to study the features of dielectric losses and their temperature dependence of ore-forming chromespinelides in relation to the chemical composition and phase transformations in their structure. Research methodology. To study the dielectric properties of chromespinelides, samples were prepared in the form of a cube with an edge of 0.02 m (two cube samples were prepared from each sample). Measurements were performed in an open system at atmospheric pressure. Dielectric losses were measured with a two-electrode setup every 10 degrees in the temperature range 20–900 °C. Heating rate is 4 deg/min. The temperature in the system was determined with a platinum-piatinum-rhodium thermoeiectric coupie at 0.01 m from the sampie. As a measuring device for determining the tangent of the angie of dielectric losses (tg δ) at alternating voitage, the “Digitai L, C, R Meter” E7-8 was used. The operating frequency of the device is 1 kHz. In the initial sample and the duplicate sampie after its roasting to 900 °C, the content of oxides of ferrous and ferric iron was determined. The reiative change in the ratios of oxide and ferrous iron in the initial sample and in the dupiicate sample after roasting was compared with the position of the maximum dielectric losses on the temperature scale. Results. Samples of chromite ore from various deposits and ore occurrences of the Urals were studied by physical, physicochemical, mineralogical and petrographic methods. The temperature dependences of dielectric losses of 21 samples of chromite ore, consisting of 80–90% of chromespinelides, were obtained. All curves clearly show the maximum dieiectric iosses. This indicates that the losses are of a relaxation nature. The position of the maximum on the temperature scaie is different for the studied chromespinelides and is mainly associated with a change in the ratio H. H value is the relative change in the ratio of oxide and ferrous iron FeO/Fe2 O3 in a chromespinelide sample during its heating to 900 °C. The position of the maximum dielectric losses for the studied samples varies from 450 °C (sampie 1 – massive chromitite from the Podenny mine III deposit – Alapaevsi<y massif) to 842 °C (sample 21 – massive chromite ore from the Tsentrainy deposit – Ray-lz massif). In this case, H vaiue varies from 1.61 to 11.14, respectively. A relationship was revealed between the position of the maximum dieiectric losses on the temperature scale of the studied samples of chromite ore and the parameter H. Conclusions. The above results in combination with other physicochemical parameters can be used as an indicator of a rapid assessment of the type of mineralization.

Thermal Analysis, Dielectric Response and Electrical Conductivity of Silicon Phthalocyanine Dichloride (SiPcCl2) Thin Films

This research is a detailed examination of the effect of post-annealing on the structure and electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films. Differential thermal analysis (DTA) is used to determine the temperature limit of thermal stability for a sample of silicon phthalocyanine dichloride (SiPcCl2). The results of differential thermal analysis (DTA) proved that silicon phthalocyanine dichloride (SiPcCl2) is thermally stable up to 415 K. The dielectric behavior and the electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films were investigated under a temperature effect from 303 K to 383 K and a frequency from 200 Hz to 20 MHz. The frequency and temperature dependence of dielectric loss and dielectric constant values were explained in terms of dielectric polarization theory. The alternative current (AC) conductivity response toward the frequency change obeys Jonscher’s power law. The correlated barrier hopping (CBH) model is utilized and adapted to fit the conduction mechanism in the high- and low-frequency regions. Both the complex electric modulus and the impedance formalisms are used to illustrate the dielectric characteristics of the silicon phthalocyanine dichloride (SiPcCl2). The potential height value of the hopping barrier, Wm, and activation energy value, Eac, for dielectric relaxation were determined.

Temperature-dependent dielectric loss in BaTiO3: Competition between tunnelling probability and electron-phonon interaction

The temperature-dependent impedance spectroscopy, optical absorption spectroscopy, and Raman spectroscopic measurements have been carried out on BaTiO3 in the temperature range from 350 K to 430 K in order to understand the possible correlation between dielectric loss measured in terms of loss tangent (tan(δ)), band gap (Eg) and electron-phonon coupling parameter (λe-ph). It has been observed that in the tetragonal phase tan(δ) increases marginally, whereas in cubic phase tan(δ) shows a decreasing trend with increasing temperature. It has been observed that λe-ph increases with temperature and shows a sudden increase by almost two-fold at tetragonal to cubic transition temperature. The marginal increase in the value of tan(δ) with temperature in tetragonal phase is understood by considering the competition between the tunnelling of electron from valence to the conduction band and electron-phonon coupling, whereas; decrease in the value of tan(δ) in the cubic phase as a function of temperature may be due to the dominating contribution of electron-phonon coupling. Present investigations clearly establish the strong correlation between the temperature dependence of dielectric loss, the value of band gap, and electron-phonon interaction.

Effect of acceptor and donor dopants (Na, Y) on the microstructure and dielectric characteristics of high Curie point PZT-modified ceramics

This study describes the preparation of a solid solution of $${\text{Pb}}^{2 + } [({\text{Zr}}_{0.05}^{4 + } ,{\text{Ti}}_{0.95}^{4 + } )_{0.97} ({\text{Al}}_{1/3}^{3 + } ,{\text{Zn}}_{1/2}^{2 + } ,{\text{W}}_{1/3}^{6 + } )_{0.03} ]{\text{O}}_{3}$$ (PZT) based on the mixed oxide method. A different amount of sodium carbonate and yttrium oxide (0.03 at.%, 0.06 at.%, and 0.1 at.%), where the ratio of Na:Y = 1:1 by mole, was added to PZT to investigate the effect of Na and Y co-doping. The ceramic samples were sintered and then subjected to phase identification, physical properties determination, and dielectric properties measurement. It was assumed that, by integrating into the lattice parameters, there is a substitution preference alternation of Y3+ for host cations in the perovskite lattice, while Na+ replaces the A-position of Pb2+ in the lattice. This resulted in more oxygen vacancy being generated in the lattice. PZT–xNY compositions exhibited an obvious anomaly in the temperature dependence of dielectric loss and dielectric permittivity below the phase transition temperature. In addition, it was found that doping of 0.1 at.% Na and Y resulted in a maximum dielectric constant (ec$$\sim 10,400$$) at Curie temperature (~ 749 K) with dissipation factor tan(δ)$$\sim 2.798$$%. Moreover, the diffusivity estimated using the modified Curie–Weiss law obtained at 1 kHz for all compositions showed that the material exhibits a diffuse-type phase.

Detection of Ageing Effect in Polyesterimide by Terahertz Time-Domain Spectroscopy

The ageing and degradation of polyesterimide (PESI) may threat the safe operation of the electrical equipment. Due to the lack of effective experimental methods, the ageing mechanism is still under debate. In this article, we employ differential scanning calorimetry and terahertz time-domain spectroscopy (THz-TDS) at variable temperatures to investigate the glass transition temperature and molecular dynamics of PESI. Ageing sample with a duration of 30 days was prepared to study the influence of hygrothermal ageing. Three peaks emerge in both absorption spectra and dielectric spectrum of ageing sample at the range of 0.2–2.25 THz. We investigate the temperature dependence of dielectric loss for both samples. Four temperature regimes and three crossover temperatures are extracted according to the slope of fitting curves. We find that the ageing treatment has different effect on the molecular dynamics in each temperature range. This indicates the evolution of ageing at various space scales. We believe that THz-TDS has immediate application potential in the detection of ageing degree and service-life evaluation.

Effects of Nd-doping on multiferroic properties of Bi<sub>6−x</sub>Nd<sub>x</sub>Fe<sub>1.4</sub>Ni<sub>0.6</sub>Ti<sub>3</sub>O<sub>18</sub> polycrystalline

Single phase polycrystalline Nd-modified BNFNT-<i>x</i> series samples are obtained from the precursors of the same chemical formula, and prepared by using the citric acid-nitrate method. The X-ray photoelectron spectroscopy measurement indicates that a slight Nd modification does not exert significant influence on the stability of the octahedral FeO<sub>6</sub>, nor NiO<sub>6</sub> nor TiO<sub>6</sub>. When the molar concentration of Nd exceeds 0.25, the stability of BiO layer is cemented and conducive to the insulating role of BiO layer. It is seen that a small quantity of Nd substitution for bismuth can improve the ferroelectric polarization (2<i>P</i><sub>r</sub>) of ～ 19.7 <inline-formula><tex-math id="Z-20190127014418-3">\begin{document}$ \mu {\rm C/cm }^2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20181287-e-lijj-revised_Z-20190127014418-3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20181287-e-lijj-revised_Z-20190127014418-3.png"/></alternatives></inline-formula>. The room-temperature magnetization (2<i>M</i><sub>s</sub>) can reach a maximal value of ～ 4.132 emu/g (1 emu/g = 10<sup>−3</sup> A·m<sup>2</sup>/g)in the BNFNT-0.20 sample. Two anomalies are observed in the temperature-dependent dielectric loss spectrum: one is situated in the temperature range from 200 K to 400 K and the other is located in the vicinity of 900 K. It is considered that the loss anomaly found near 900 K might be associated with the viscous motion of ferroelectric domain walls. In addition, the loss peak shown in a temperature range from 200 K to 400 K shifts toward the higher temperature with measuring frequency increasing, indicating the characteristics of dielectric relaxor behavior. The activation energy is evaluated to be 0.287−0.366 eV, which suggests that the relaxor is associated with the electrons transfer and hop between Fe<sup>3+</sup> and Fe<sup>2+</sup>. The room-temperature magnetization (2<i>M</i><sub>s</sub>) has reached a maximal value of ～ 4.132 emu/g in the BNFNT-0.20 sample. The lattice distortion due to the introduction of Nd changes the angle of such antiferromagnetic coupling bonds as Fe<sup>3+</sup>—O—Fe<sup>3+</sup>, Fe<sup>3+</sup>—O—Ni<sup>3+</sup> and Ni<sup>3+</sup>—O—Ni<sup>3+</sup>, which leads the AFM spin states to break, and thus increases the magnetic properties. While with further modification of Nd, the drastic lattice distortion reduces the occupation of the B-sites of the magnetic ions, which might be responsible for further deteriorating the magnetic properties.

The impact of Eu3+ ion substitution on dielectric properties of Y3−xEuxAl5O12 (0.00 ≤ x ≤ 0.10) ceramics

This study reported the effect of Eu substitutions on the conductivity and dielectric properties of Y3−xEuxAl5O12 (0.0 ≤ x ≤ 0.1), YAG:xEu3+. All products were fabricated by solid state route. The formation of YAG was approved through X-ray diffraction powder diffraction and high-resolution transmission electron microscope. It was found that the lattice parameters are increasing with increase the substitution content due to the difference in ionic radii between Y3+ and Eu3+. Electrical and dielectric properties of YAG (Y3Al5O12) and YAG:xEu3+ ceramics were investigated extensively for a variety of concentrations (0.00 ≤ x ≤ 0.1) of the substitutional Eu3+ ion from the 4f lanthanide group. The temperature dependence of dielectric loss, dielectric constant, loss tangent and ac/dc conductivity were examined up to 5.0 MHz to understand the electrical and dielectric properties for both doped and undoped YAG ceramics. The experimental results revealed that Eu3+ ion substitutions (especially x = 0.05) in YAG ceramics meaningfully influence the lossy mechanisms, conductivity and dielectric constant which is probably due to the contribution to the conduction mechanism of the 4f–Eu and 3d–Al ions. So, this can be incorporated at the exceptional sites of both Oh (octahedral) and Td (tetrahedral) symmetries in YAG: xEu3+ ceramics.

Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 [xBZT-(1-x)BCT] ceramics, with x = 0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (TR-T) of 40 °C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (TT-C) of 110 °C. The dielectric analysis suggests that the phase transition at TT-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A1, E(LO) Raman mode. The saturation polarization (Ps) ≈8.3 μC/cm2 and coercive fields ≈2.9 kV/cm were found to be optimum at composition x = 0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 105 cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high TT-C (110 °C), a high dielectric constant (εr ≈ 12,285) with low dielectric loss (0.03), good polarization (Ps ≈ 8.3 μC/cm2) and large recoverable energy density (W = 121 mJ/cm3) with an energy storage efficiency (η) of 70% at an electric field of 25 kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.

Structural and electrical characterization of La2ZnMnO6 double perovskite

Polycrystalline La2ZnMnO6 (LZM) compound was synthesized successfully by solid state reaction route with single phase orthorhombic structure (Pnma space group) as revealed by X-ray diffraction analysis. The microstructure of LZM has inhomogeneous distributions of grains and average grain size is varying from 0.05 to 5.0 μm. EDAX survey showed Zn rich lines with an uneven distribution of the atoms. Peaks in Raman spectrum of LZM compound correspond to MnO bond stretching and tilt of the MnO octahedral. The dielectric behavior of ceramics in lower frequency regions exclusively depends on grain boundary effect. The temperature dependent dielectric loss study shows relaxation peaks dominating at lower frequencies and shifted towards higher temperature range with increasing frequency. The strong influence of non-Debye type relaxation is confirmed by Bergman fitting to experimentally observe electric modulus curve. VRH model has been used to study conduction behavior of the sample.

Synthesis and piezoelectric properties of (1 − x)Bi0.5(Na0.8K0.2)0.5TiO3–xSr2ZrTiO6 ceramics

The effects of Sr2ZrTiO6 (SZT) addition on the piezoelectric properties of (1 − x)Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT)–xSZT ceramics were characterized in this study. The X-ray powder diffraction (XRPD) profiles and Raman spectra of the ceramics in the composition range of 0–0.02 implies the presence of morphotropic phase boundary (MPB) which consists of the rhombohedral and tetragonal phases. Moreover, the temperature dependence of dielectric loss indicated a presence of the ferroelectric–relaxor transition temperature (TF–R) of around 75 °C for x = 0.005 and the temperature dependence shifted to a lower temperature at x = 0.01. The temperature dependence of the P–E hysteresis loop of the ceramics at the compositions of x = 0.005–0.02 showed pinched hysteresis loops above TF–R. Regarding the piezoelectric constant (d33), it was increased by SZT addition in the MPB region (x = 0–0.01) and the highest d33 of 202 pC/N was obtained at the composition of x = 0.0025. The S–E unipolar loop was also evaluated, the strain of the ceramic increased up to x = 0.02; and the highest pm/V was obtained at the composition of x = 0.02.

Dielectric properties of layered FeGaInS4 single crystals in an alternating electric field

The results of investigations of the frequency and temperature dependences of dielectric losses and the imaginary part of the dielectric permittivity in FeGaInS4 single crystals are presented. Their experimental values are determined. It is established that the loss tangent and the imaginary part of the permittivity of FeGaInS4 single crystals in a field with frequencies of 104–106 Hz decrease inversely proportional to the frequency (tanδ ~ 1/ω), and the conductivity is characterized by the band–hopping mechanism. For FeGaInS4, the relaxation time is calculated, and it is established that there is a mechanism of electron polarization caused by thermal motion in this crystal.

Origin of thermal depolarization in piezoelectric ceramics

PZT, BSPT, PT, and two lead-free Bi2WO6, as five of the most representative piezoelectric systems with different Curie points were selected to study the origin of thermal depolarization in piezoelectric ceramics. The temperature dependences of dielectric loss and dielectric constant curves show that dielectric loss peaks of PZTMN, BSPTPNW, PTBFM, BWLi, and BWLa are at 330°C, 392.2°C, 495°C, 598.8°C, and 781°C, respectively. The results of thermal depoling measurement show that the depolarization temperature is closely related to the dielectric loss peak. And the peak points of dielectric loss curves below or at the Curie temperature are the points of complete depolarization.

The Structure and Complex Impedance Spectroscopy of Sr1-xCaxBi4Ti4O15 (x=0, 0.2, 0.4, 0.6, 0.8) Ceramics

In the present work, we have synthesized polycrystalline Sr1-xCaxBi4Ti4O15 [x=0, 0.2, 0.4, 0.6, 0.8] ceramics by solid state reactive technique. The analysis indicates that the ceramics present an orthorhombic structure with grains exhibit a plate like morphology. Dielectric relaxations of the above compositions were investigated in the temperature range 100–6000C. Using the Cole–Cole plots, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The presence of the peaks in temperature dependent dielectric loss indicates that the hopping of charge carriers is responsible for the relaxation. Impedance studies indicate a non-Debye type relaxation and with increase in temperature relaxation frequency shift to higher side. A notable shift in impedance loss peaks towards higher frequency side explains the conduction in material. The Nyquist curve shows overlapping semicircles, for grain and grain boundary for all the compositions. The frequency dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated process and the spectra follow the universal power law. The conductivity is frequency independent at low temperatures. The variation of DC conductivity confirms that the samples Sr1-xCaxBi4Ti4O15 [x=0: SBT, 0.2: SCBT02, 0.4:SCBT04, 0.6:SCBT06, 0.8:SCBT08] exhibits negative temperature coefficient of resistance behavior at high temperatures.

立方核壳晶粒模型的分布介电效应

用立方晶粒模型模拟多面体核壳结构，得到了有效介电常数与核壳尺寸的关系。当壳层为极薄的低介电常数时，该关系表现为晶粒尺寸效应：介电峰移向低温及介电常数下降；当壳层较厚且核与壳介电常数峰不同时，核对介电常数的贡献为其尺寸平方比相关的线性叠加关系。二阶铁电相变时，分布的居里温度会使介电峰向高温移动，同时介电常数减小；分析结果发现：其顺电相介电隔离率的温度关系不能用幂律表示。壳层居里温度的线性分布与核的高斯分布结合能够得到较为平稳的介电常数温度关系。认为铁电体极化强度的平方相当于偶极子的作用，利用偶极子复介电常数关系，导出了分布式铁电相变的损耗温度关系。A model of cubic core-shell grain with the distribution of the Curie temperature is proposed for simulation of the polyhedron core-shell structure to obtain the size related dielectrics. When the shell is a very thin layer with low dielectric constant, the shell has the grain-size effect: dielectric constant decreases and the peak moves to low temperature. When the shell is thick with different dielectric peak from the core one, the contribution of the core to the dielectric constant is a linear relation to the square of it size. The distribution of the Curie temperature will move dielectric peak to high temperature with dropping dielectric constant, and the temperature relation of im-permeability in paraelectric phase can not be expressed by the power-law. Ferroelectrics will have high stability of relation of dielectric constant with temperature for the combination of the shell in linear distribution and the core in Gaussian distribution. It is the square of spontaneous polariza-tion in ferroelectrics that has the same function as dipole in dielectrics for contribution to the complex dielectric constant, and therefore a temperature dependent dielectric loss of the distri-bution of the Curie temperature is derived.

Synthesis, thermo physical and electrical properties of Nd 2-xLi xTi 2O 7-δ

Nd 2-xLi xTi 2O 7-δ (x = 0, 0.1 and 0.15) (NDT) was synthesised by Gel Entrapment Technique. These ceramics were structurally characterized by analysis of X-ray diffraction (XRD) patterns, indicates that NDT ceramics present a monoclinic structure. Proton Induced Gamma Emission (PIGE) technique was used to determine the Li content in the as synthesised and sintered samples. Dielectric relaxations of these compounds were investigated in the temperature range 250 °C–900 °C. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The observed loss tangent was very low for the base material and by doping with Li the dielectric loss found to increase. The presence of the peaks in temperature dependent dielectric loss indicated that the hoping of charge carriers is responsible for the relaxation. The Nyquist plot shows overlapping semicircles, for grain and grain boundary of NDT ceramics. The variation of dc conductivity confirmed that the NDT's exhibit negative temperature coefficient of resistance behavior in high temperature. Studies indicated onset of the grain boundary conduction process occurs even at lower temperatures in these systems with increase in the Li content.

Dielectric loss in ore-forming chromium spinel at temperatures from 20 to 800 °C

Physical, physicochemical, and mineralogical-petrographic methods have been applied to samples of ophiolite-hosted chromite ore from different deposits and occurrences in the Urals. Temperature dependences of dielectric loss obtained for nine chromite ore samples consisting of 95–98% Cr spinel show prominent peaks indicating a relaxation origin of the loss. The analyzed samples have the loss peaks at different temperatures depending mainly on H = (FeO/Fe 2O 3) ⁎ : (FeO/Fe 2O 3) ⁎⁎, where (FeO/Fe 2O 3) ⁎ and (FeO/Fe 2O 3) ⁎⁎ are, respectively, the ferrous/ferric oxide ratios in the samples before and after heating to 800 °C, and H is thus the heating-induced relative change in the FeO/Fe 2O 3 ratio. These peak temperatures vary from 550 °C (sample 1, high-Cr chromium spinel with more than 52% Cr 2O 3) to 750 °C (sample 2, aluminous and magnesian spinel with less than 30% Cr 2O 3), and H ranges correspondingly from 1.61 to 5.49. The temperature of the loss peaks is related with H as H = 34.30 − 11.52 N + 1.20 N 2, with an error of σ = 0.19 ( N = T · 10 −2, T is temperature in °C).

Temperature and frequency dependence of dielectric loss of Ba(Mg 1/3Ta 2/3)O 3 microwave ceramics

Ba(Mg 1/3Ta 2/3)O 3 ceramic possessing extremely high Q × f value of more than 300 THz at microwave frequency was developed in our previous study. It is of great interest to understand the mechanism of microwave absorption in such a practical material. In the present study we report on the temperature dependence of the dielectric loss in the Ba(Mg 1/3Ta 2/3)O 3. The mechanism of the microwave absorption is discussed using two phonons difference process. The samples were prepared by conventional solid state reaction and sintered at 1893 K in oxygen atmosphere. Dielectric properties in the microwave range were measured by Hakki & Colemann and resonant cavity methods in the temperature range of 20–300 K. Whispering gallery mode technique was used for the measurement of the dielectric properties at the millimeter wave frequency. Dielectric loss of the Ba(Mg 1/3Ta 2/3)O 3 at the microwave frequency increases with temperature between 200 and 300 K in general agreement with the theory of intrinsic dielectric loss derived from the two phonon difference process. However below 200 K, the dielectric loss has shown a distinctive behavior with a loss peak at 40 K. It was inferred that the loss peak of the Ba(Mg 1/3Ta 2/3)O 3 was caused by the local orientation polarization having dispersion at the microwave frequency.

Impedance spectroscopy and morphology of SrBi 4Ti 4O 15 ceramics prepared by soft chemical method

In this work, we have synthesized polycrystalline SrBi 4Ti 4O 15 (SBiT) ceramics by soft chemical method. These ceramics were structurally characterized by analysis of X-ray diffraction (XRD) patterns, indicates that SBiT ceramics present an orthorhombic structure. Scanning electron micrograph shows that the grains exhibit a plate like morphology. Dielectric relaxations of the SBiT ceramics were investigated in the temperature range 100–700 °C. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The presence of the peaks in temperature dependent dielectric loss indicates that the hoping of charge carriers is responsible for the relaxation. Impedance studies shows a non-Debye type relaxation, and relaxation frequency shift to higher side with increase in temperature. A significant shift in impedance loss peaks towards higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. The Nyquist plot shows overlapping semicircles, for grain and grain boundary of SBiT ceramics. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated process and the spectra follow the universal power law. The hopping frequency shifts towards higher frequency side with increase of temperature, below which the conductivity is frequency independent. The variation of dc conductivity confirms that the SBiT ceramics exhibits negative temperature coefficient of resistance behavior in high temperature.