Temperature Dependence Of Dielectric Properties Research Articles

Effect of octahedral tilting on antiferroelectric phase stabilization in (1-x)NaNbO3-xCdTiO3 ceramics

In the present work, a unique case for the stabilization of the antiferroelectric phase in NaNbO3 has been presented, where the desired results were obtained in spite of it defying the set pattern predicted by researchers to date for achieving similar results. Antiferroelectric phase stabilization of NaNbO3 was achieved with doping of 1% CdTiO3, which is much lower compared to other dopants reported earlier. From the Rietveld refinement of x-ray diffraction (XRD) patterns, structural changes with respect to octahedral tilting were found to be responsible for the increase in energy barrier required for stabilizing antiferroelectric P over ferroelectric Q phase in (1-x)NaNbO3-xCdTiO3 ceramics. Temperature-dependent dielectric properties implied a shift in Curie temperature with an increase in CdTiO3 concentration. P-E hysteresis loop measurement demonstrated a square-shaped ferroelectric loop for NaNbO3 ceramic, while the antiferroelectric double hysteresis loop was observed for composition x = 0.01 and x = 0.02. The results were verified by observing characteristic superlattice peaks in the XRD patterns.

Broadband Dielectric Properties of Ex Vivo Bovine Liver Tissue Characterized at Ablative Temperatures

To investigate the thermal and frequency dependence of dielectric properties of ex vivo liver tissue - relative permittivity and effective conductivity - over the frequency range 500 MHz to 6GHz and temperatures ranging from 20 to 130°C. We measured the dielectric properties of fresh ex vivo bovine liver tissue using the open-ended coaxial probe method (n = 15 samples). Numerical optimization techniques were utilized to obtain parametric models for characterizing changes in broadband dielectric properties as a function of temperature and thermal isoeffective dose. The effect of heating tissue at rates over the range 6.4-16.9°C/min was studied. The measured dielectric properties were used in simulations of microwave ablation to assess changes in simulated antenna return loss compared to experimental measurements. Across all frequencies, both relative permittivity and effective conductivity dropped sharply over the temperature range 89 - 107°C. Below 91°C, the slope of the effective conductivity changes from positive values at lower frequencies (0.5-1.64GHz) to negative values at higher frequencies (1.64-6GHz). The maximum achieved correlation values between transient reflection coefficients from measurements and simulations ranged between 0.83 - 0.89 and 0.68 - 0.91, respectively, when using temperature-dependent and thermal-dose dependent dielectric property parameterizations. We have presented experimental measurements and parametric models for characterizing changes in dielectric properties of bovine liver tissue at ablative temperatures. The presented dielectric property models will contribute to the development of ablation systems operating at frequencies other than 2.45GHz, as well as broadband techniques for monitoring growth of microwave ablation zones.

Dielectric, magnetic and humidity properties of Mg–Zn–Cr ferrites

Abstract In this study, Cr3+ substituted Mg0.75Zn0.25CrxFe2-xO4 (x = 0, 0.1, 0.3) (Mg–Zn–Cr) ferrites have been synthesized using chemical co-precipitation method. The crystal structure and phase formation of Mg–Zn–Cr ferrites have been analyzed by X-Ray diffraction (XRD) method. The crystal size (from 15.37 nm to 10.84 nm) and lattice constant (from 8.405 A to 8.384 A) of the crystallized in cubic crystal structure Mg–Zn–Cr samples decreased with Cr3+ contribution. The change in lattice strain determined by Williamson-Hall (W–H) graphs. Morphological and elemental analysis were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The variations in temperature-dependent dielectric properties of samples between 290 K and 700 K were examined in the range from 20 Hz to 10 MHz. Curie temperature, where maximum dielectric constant is observed, shifted low temperatures with increasing Cr3+ contribution. This peak shift indicates that the materials have a relaxor ferroelectric character in accordance with the literature. Impedance analysis of Mg–Zn–Cr ferrites were investigated using Nyquist curves and relaxation process confirms Cole-Cole model. The magnetic properties of the samples in the range of ±5 kOe at 300 K were examined with the help of the Vibrating Sample Magnetometer (VSM). The M − H hysteresis loops of all samples showed the characteristic properties of soft magnetic materials. Finally, the effect of relative humidity (%RH) on the impedance of samples for different frequency values was investigated.

Vanadium-Oxide-Based Thin Films with Ultra-High Thermo-Optic Coefficients at 1550 nm and 2000 nm Wavelengths.

In this paper, the temperature-dependent dielectric properties of vanadium-sesquioxide-based thin films are studied to assess their suitability for thermally tunable filters at optical communication wavelengths. Spectroscopic ellipsometry is utilized to measure the optical constants of vanadium oxide thin films at temperatures ranging from 25 °C to 65 °C. High thermo-optic coefficients (dn/dTs) were observed. The highest dn/dTs, measured at approximately 40 °C, were −8.4 × 10−3/°C and −1.05 × 10−2/°C at 1550 nm and 2000 nm, respectively.

Effects of La3+ addition on the phase transition, microstructure, and electrical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

Rare earth-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics demonstrated moderately improved properties rather than undoped counterpart. In this investigation, we report the synthesis and characterization of La3+-doped BCZT (x = 0.00, 0.02, 0.04, 0.06, and 0.08) single-phase crystals prepared by high-temperature (~ 1300 °C) solid-state reaction technique. Rare earth ions addition to BCZT affects its microstructure, phase transition, and electrical properties. All compounds were crystallized in tetragonal structure at room temperature. Scanning electron microscopy (SEM) recorded the microstructural analysis of the compounds. Temperature-dependent dielectric and impedance properties of the sintered pellet were estimated at chosen frequencies as a function of temperature. Here, efforts were made to improve the electrical properties of the material with the addition of La3+ in the BCZT system. The obtained data revealed that Curie temperature (TC) diminishes with the introduction of La3+ in BCZT ceramics. Besides, the diffusivity analysis and conductivity studies were used for better comprehension of the electrical processes in the materials. The obtained lead-free ceramics with enhanced electrical properties could be utilized in the fabrication of electronic devices.

Perovskite BiFeO3–BaTiO3 Ferroelectrics: Engineering Properties by Domain Evolution and Thermal Depolarization Modification

AbstractBismuth ferrite (BFO)‐based ceramics with large electromechanical response are important in electronic device applications. To better understand their physical mechanisms, a new phase diagram established by temperature dependence of dielectric properties, temperature dependence of piezoelectric coefficient, and the evolution of their properties is proposed to explain the contribution of piezoelectric and strain response by comparing ferroelectric (FE) and relaxor ferroelectric (RFE) compositions. The FE components with macrodomains have large piezoelectric constant (d33 of 412 pC/N) at high temperature. The RFE components with nanodomains possess giant strain response (Suni = 0.37%) at 180 °C. Combined with in situ and ex situ techniques, the physical mechanisms behind the enhancement of these properties are explored. Macrodomains and multipolar phase coexistence contribute to the piezoelectricity improvement. Nanodomains and an unstable depolarization temperature (Td) region engineer the strain enhancement, which can promote electric‐field‐induced domain switching, lattice strain, and irreversible phase transition. In particular, the Td region of BiFeO3‐based ceramics has been ignored for several years, although it is actually an effective medium to engineer properties. The proposed phase diagram and dynamic model can be used to well understand the structural origins of large electromechanical properties in BFO‐based ceramics, which can give some guidance to explore materials with excellent properties for different applications.

Multiphase coexistence and enhanced piezoelectric properties in (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 lead-free ceramics

A new lead-free piezoelectric solid solution system with the formula of (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 were prepared using a conventional solid-phase sintering method, and we investigated the relationship between the composition, microstructure, phase structure and electrical properties of the ceramics. It was found that adding Bi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 induced the ceramics transition from a single orthorhombic structure to a coexistence of multiple phases, and a three-phase coexistence of rhombohedral, orthorhombic and tetragonal phases was present in the composition range x = 0.03 to 0.035. Enhanced piezoelectric properties were obtained for the ceramics near the three-phase coexistence region, with the largest piezoelectric constant d33 of 253 pC/N and the highest planar electromechanical coupling coefficient of 0.36. Additionally, a rough phase diagram for the solid solution system was established by using the critical temperatures determined by the temperature-dependent dielectric properties. The authors believe that these results can provide a useful reference for the development of (K,Na)NbO3-based lead-free piezoelectric ceramics.

The Behavior of 33PbYb1/2Nb1/2O3–22PbZrO3–45PbTiO3 Ceramic Solid Solutions in an Electric Field

The temperature dependences of dielectric properties and the time-dependent dielectric permittivity are investigated for 33PbYb1/2Nb1/2O3–22PbZrO3–45PbTiO3 ceramics in electric fields with 0 < E < 8 kV/cm. Our data show that a small fraction of pseudocubic relaxor phase is present along with rhombohedral and tetragonal phases in the phase that exists in this material below the morphotropic transition temperature. In contrast to other relaxors, the dielectric permittivity of the phase existing below the morphotropic phase transition temperature does not vary with time in an applied electric field. The causes of such behavior are discussed.

Association of structural strains and dielectric relaxation in Co-doped Sr-Hexaferrites

Sr-hexaferrites nanoparticles were co-doped with composition SrFe12-2xCrxZnxO19 (x = 0.0–1.0) using co-precipitation method. X-ray diffraction (XRD) showed hexagonal structure. The crystallite size for calcined and sintered samples were in the range of 34–84 nm and 42–67 nm, respectively. Strains were determined by Williamson-Hall analysis. With increase in amount of Cr–Zn dopant in the samples, values of strains showed a non-monotonous behavior. Scanning Electron Micrographs (SEM) revealed the agglomeration of particles. At two fixed frequencies, 500 kHz and 1-MHz the temperature dependent dielectric and impedance properties were investigated over a temperature range 100 °C–500 °C. Dielectric transition temperature Td was observed to be in range of 400 °C–500 °C for all the prepared samples. DC electrical resistivity showed a decreasing trend with respect to temperature. Activation energies showed two regions of temperature dependence. Sample (x = 0.2) with maximum resistivity might be used as an energy efficient material.

Enhanced piezoelectric properties of Mn‐modified Bi5Ti3FeO15 for high‐temperature applications

AbstractBi5Ti3FeO15 (BTF) has recently attracted considerable interest as a typical multiferroic oxide, wherein ferroelectric and magnetic orders coexist. The ferroelectric order of BTF implies its piezoelectricity, because a ferroelectric must be a piezoelectric. However, no extensive studies have been carried out on the piezoelectric properties of BTF. Considering its high ferroelectric‐paraelectric phase transition temperature (Tc ~ 761°C), it is necessary to analyze the piezoelectricity and thermal stabilities of BTF, a promising high‐temperature piezoelectric material. In this study, lightly manganese‐modified BTF polycrystalline oxides are fabricated by substituting manganese ions into Fe3+ sites via the conventional solid‐state reaction method. X‐ray diffraction and Raman spectroscopy analyses reveal that the resultant manganese‐modified BTF has an Aurivillius‐type structure with m = 4, and that the substitutions of Fe by Mn lead to a distortion of BO6. The temperature‐dependent dielectric properties and direct‐current (DC) resistivity measurements indicate that the Mn ions can significantly reduce the dielectric loss tanδ and increase the DC resistivity. The piezoelectricity of BTF is confirmed by piezoelectric constant d33 measurements; it exhibits a piezoelectric constant d33 of 7 pC/N. Remarkably, BTF with 4 mol% of Mn (BTF‐4Mn) exhibits a large d33 of 23 pC/N, three times that of unmodified BTF, whereas the Curie temperature Tc is almost unchanged, ~765°C. The increased piezoelectric performance can be attributed to the crystal lattice distortion, decreased dielectric loss tanδ, and increased DC resistivity. Additionally, BTF‐4Mn exhibits good thermal stabilities of the electromechanical coupling characteristics, which demonstrates that manganese‐modified BTF oxides are promising materials for the use in high‐temperature piezoelectric sensors.

Temperature dependence on dielectric properties of CdTe and ZnTe using first-principles method and experimental data

The dielectric properties of ZnTe and CdTe at high temperature are studied by both of vibrational frequencies and experiment damping constants. We perform systematic calculations to investigate the vibrational properties of perfect crystalline ZnTe and CdTe for a wide range of temperature ranging from 0K to 1400K by combining the first-principles methods and quasi-harmonic approximation (QHA). Then, this method is performed to estimate the temperature dependence of dielectric properties of ZnTe and CdTe with the transverse-optical (TO) and longitudinal-optical (LO) mode frequencies and the damping coefficient obtained from experimental data under lower temperature. Furthermore, we extended the estimations of dielectric properties of ZnTe and CdTe to higher temperatures.

Morphological study and optoelectrical properties of Zn2+ substituted nickel ferrite nanoparticles

In this study a series of spinel ferrites having formula Ni(1-X)ZnXFe2O4 and substituted with Zn (where X = 0–1, ΔX = 0.2) were prepared by sol gel auto-combustion route using microwave. The crystallite size and its morphology have been analysed by TEM. The average particle size obtained from TEM is about 24–26 nm. EDX study is applied to confirm the elemental compositional proportion of prepared ferrite powder. FTIR analysis revealed the presence of characteristic absorption bands corresponding tetrahedral and octahedral sites confirmed the ferrite samples are formed. The temperature and frequency dependent dielectric properties were studied with impedance analyser. The Maxwell Wagner grain and grain boundary layer model of poly-crystalline ferrite can explain the enhancement of AC conductivity with frequency.

Dielectric and ferroelectric behaviour of Zr-doped BaTiO3 perovskites

The crystal structure, microstructure, dielectric and ferroelectric behaviour of Ba(ZrxTi1-x)O3 (x = 0.05, 0.10, 0.15, 0.20, 0.25) perovskites fabricated by high-temperature solid state method were investigated. Zr4+ ions are dissolved completely into B-site of the matrix BaTiO3 within the studied composition range, leading to an expansion of the lattice. The average grain size decreased with Zr content increasing. In P-E loops, the remanent polarization gradually decreased with Zr-doping, indicating the depression of ferroelectricity. Temperature dependent dielectric properties at different frequencies exhibited obvious relaxor behaviour. It was shown that diffuseness coefficient increased from 1.45 (x = 0.05) to 1.89_1.90 (x = 0.10-0.25) by using the modified Curie-Weiss law for the fit. The permittivity of the Ba(ZrxTi1-x)O3 ceramics at room temperature was largely improved by Zr-doping, thus when x = 0.20, r (1 kHz) = 10790.

Flexible alizarin red/PVA composites with colossal dielectric and high power laser filtering properties

Dye/polymer composite is gradually emerging as an indispensable component of the modern optoelectronics technology due to their fascinating optical, mechanical and electrical properties. Here, we investigate the structural, mechanical, optical and electrical properties of the economical, self-standing, flexible alizarin red (AR)/poly (vinyl alcohol) (PVA) composites (AR concentration 0 wt %, 0.1 wt %, 1.0 wt %, 2.0 wt %) prepared by facile solution casting technique. The UV–Vis absorption spectroscopy results in higher absorption of the composites with increasing AR dye concentration in the UV–Vis region (200–600 nm). A 2.0wt % AR/PVA composite film of thickness 250 ± 30 µm can entirely block light in the 200–600 nm wavelength region and can effectively block high power laser irradiation (10.7 mW) of wavelength 544 nm for a period of 60 min without degrading itself, which makes AR/PVA a potential candidate for flexible, high power laser filter in 200–600 nm region. A significant reduction in the band gap (~ 3.1 eV) is also observed for the composites than that of the neat PVA. The dielectric constant (\(\varepsilon^{\prime}\)) is found to be increased significantly with incorporation of AR dye and an optimum value of \(\varepsilon^{\prime} =\) 208 (at 40 Hz and 300 K) is obtained for 2.0% AR/PVA with small \(\tan \delta\) value (~ 0.56). Temperature-dependent dielectric properties of the composites are also investigated which confirm the dominating role of the interfacial polarization and presence of multiple dielectric relaxation processes. The enhanced laser filtering and dielectric properties of the AR/PVA composites can be attributed to the formation of hydrogen bond-mediated complexes in the composites. The fabricated novel AR/PVA composites can be potentially used in flexible, low-cost laser filter and flexible energy storage devices.

Enhanced energy density in Mn-doped (1-x)AgNbO3-xCaTiO3 lead-free antiferroelectric ceramics

Ceramics of 0.2 wt% Mn-doped (1-x)AgNbO3-xCaTiO3 (x = 0.00–0.04) were prepared in flowing oxygen with the solid state method. The microstructure, antiferroelectricity and energy storage performance were investigated to explore the potential for use in energy storage capacitors. Incorporation of CaTiO3 in AgNbO3 effectively inhibits the grain growth and gives rise to high dielectric breakdown strength. The temperature-dependent dielectric property and Raman spectroscopy measurements demonstrate the enhanced stability of antiferroelectricity by CaTiO3 addition through adjusting the M1–M2 phase transition. As a result of both improved antiferroelectricity and dielectric breakdown strength, a high recoverable energy density of 3.7 J/cm3 was achieved in the 2 mol% CaTiO3-modified AgNbO3 ceramic, which represents one of the highest recoverable energy density in recently studied lead-free ceramics. Furthermore, the energy storage performance displays an excellent thermal stability with a low variation (3%) over a wide temperature range (20–120 °C). These results indicate that modifying AgNbO3 simultaneously on the A- and B-sites in the ABO3 perovskite structure may lead to the discovery of new antiferroelectric materials with a high energy density.

Stirring-mediated anomalous dielectric behaviour of electrodeposited and in situ oxidized FeAl2O4 thin films

Spinel ferrites, due to high permeability and stability, possess remarkable features that make them a favourable candidate for spintronic applications. Electrodeposition method is used for the synthesis of iron aluminium oxide (FAO) thin films. A series of samples are prepared by keeping deposition time constant at 10 min, and in situ oxidation time varied as 5 min, 10 min, 15 min and 20 min by anodic electrodeposition. These electrodeposited FAO thin films are annealed at 500 Oe applied magnetic field at 300 °C in vacuum. At 5-min oxidation time, mixed structural phases, i.e. FeAl2O4 and Al2O3, are observed, whereas phase-pure FeAl2O4 is observed at 10-min oxidation time. A further increase in oxidation time to 15 min and 20 min results in reappearance of mixed phases. Phase-pure FeAl2O4 thin film at oxidation time of 10 min exhibits bond angle of ~ 158.59° with + ive tilt ~ 4.59°. A decrease in bond angle (i.e. ~ 139.20°) with − ive tilt ~ − 14.8° is observed with an increase in oxidation time to 20 min. SEM micrographs show the formation of octahedral and dodecahedral grains for 10-min oxidation time with grain size in the range of 2–3 μm. FTIR and Raman analysis confirms the formation of FeAl2O4 thin film at 10-min oxidation time with the appearance of bands at 610.94 cm−1 and 753 cm−1, respectively. Magnetic hysteresis curves show a ferromagnetic behaviour of iron aluminium oxide thin films. Thin film prepared using 10-min oxidation time shows a relatively higher value of saturation magnetization Ms (17.89 emu/cm3). Anomalous dielectric behaviour is observed for FeAl2O4 thin films due to the resonance phenomena at higher frequencies. Dielectric constant of ~ 37.96 at log f = 5.0 is observed for 10-min oxidation time. Temperature-dependent dielectric study is also carried out in the temperature range of 30–210 °C. Fitting of Cole–Cole plots through ZView software shows a strong dependence of dielectric constant on grain boundary resistance. This is to be emphasized that detailed study on the dielectric and impedance properties of electrodeposited iron aluminium oxide thin films is rare to be found. Having knowledge of room temperature and temperature-dependent dielectric properties of iron aluminium oxide thin films will help in extending the field of application to the microelectronic industry.

Microfluidic temperature sensor based on temperature-dependent dielectric property of liquid**Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant No. LQ19F010007), the National Natural Science Foundation of China (Grants Nos. 61901146 and 61874038), and the Smart City Collaborative Innovation Center of Zhejiang Province, China.

We propose a low-cost compact microfluidic temperature sensor by virtue of the temperature-dependent permittivity of liquid. The sensor is composed of a coplanar waveguide (CPW) transmission line loaded with three resonators and a microfluidic plate with three channels. The resonant frequency of each resonator relies on the temperature-dependent dielectric property of liquid in corresponding channel, which therefore can be used to extract the temperature. The proposed sensor features a compact size and low cost since it requires only micro fluid volume instead of additional electronic components to produce significant frequency shift with changing temperature. Moreover, it exhibits decent accuracy and stability in a temperature sensing range from 30 °C to 95 °C. A theoretical analysis of the sensor is provided, followed by the detailed characterization method, and a prototype is designed, manufactured, and measured to verify the theoretical analysis.

Near-field radiative thermal rectification assisted by black phosphorus sheets

We suggest a thermal rectification structure where a semi-infinite InSb plate and a semi-infinite 3C–SiC plate coated by black phosphorus (BP) sheets are separated by a nanoscale vacuum gap. To obtain high and tunable thermal rectification efficiency, we employ the temperature-dependent dielectric properties of both InSb and 3C–SiC, and introduce BP sheets with in-plane anisotropy into the structure. Based on fluctuational electrodynamics, the near-field radiative heat transfer and the rectification efficiency are calculated. It is found that the rectification efficiency varies very sensitively with the emitter's temperature, the chemical potential and the number of BP layers, thus opening up possibilities to control the rectification efficiency through these parameters. Higher rectification efficiencies are obtained under some certain conditions, and the origins of the thermal rectification effect are elucidated in some detail. The obtained results might be helpful in designing a BP-based high-efficiency thermal diode.

Preparation and investigation of structure, magnetic, and dielectric properties of (1 − x)Bi2Fe4O9–xMgFe2O4 bicomponent ceramics

Crystal structure, morphology, magnetic, and dielectric properties of (1 − x)Bi2Fe4O9–xMgFe2O4 bicomponent ceramics are investigated in detail. The material has been synthesized via sol–gel method. Analysis of X-ray diffraction data of the bicomponent ceramics shows the coexistence of orthorhombic Bi2Fe4O9 and spinel MgFe2O4 phases with no third phase. Microstructural and surface morphology displays the homogeneous grain distribution with different grain sizes of Bi2Fe4O9 and MgFe2O4. The magnetic measurement shows decreasing coercivity and increasing values of remnant and saturation magnetization with the increase in MgFe2O4. Temperature-dependent dielectric properties and electrical modulus are conducted in the temperature range of 27–527 °C with the frequency ranging from 1 to 30 kHz. Two abnormal peaks are, respectively, observed at low and high temperature ranges. The variation of electric properties is closely related to the composition of MgFe2O4. The results of dielectric and electrical modulus indicate the appearance of dielectric relaxation in (1 − x)Bi2Fe4O9–xMgFe2O4. Combined with the study of activation energy, the dielectric relaxation is mainly induced by different electric responses of various charge carriers intrinsically dominating in a thermally activated process with the incorporation of MgFe2O4. The combination of Bi2Fe4O9 and MgFe2O4 enhances the coexistence of magnetic and electric properties in the present composites. It is quite promising from application point of view.

Less temperature-dependent high dielectric and energy-storage properties of eco-friendly BiFeO3–BaTiO3-based ceramics

The effects of eco-friendly (BiNa0.84K0.16)0.48Sr0.04TiO3 (BNKS)-content in 0.65Bi1.05FeO3–0.35BaTiO3 (BFBT) dielectrics were investigated by following simple solid state fabrication route. By the introduction of BNKS in BFBT matrix the average grain size was significantly reduced, with relatively high dense microstructure (relative density > 94%). The BNKS-modified BFBT dielectrics demonstrated thermally-stable εr (670–1005, from 30 °C to 500 °C), high Tmax (424 °C–465 °C), colossal εr-max (58880–69226), and εr-mid (2891–5652 ± 15%) across the broad range of temperature from 244 °C to 500 °C. At the optimum composition (x = 0.10) the temperature-dependent (30 °C–150 °C) substantially high energy-storage density (Wstore ∼ 0.81 J/cm3) and efficiency (η > 60%) in bulk ceramics were observed. The thermally-stable dielectric and energy storage properties suggest that present investigated dielectrics can be promising candidates for high temperature dielectric applications and power electronics.