Temperature Coefficient Of Permittivity Research Articles

Effects of O2/Ar Ratio on Preparation and Dielectric Properties of CaZrO3 Films by Radio Frequency (RF) Magnetron Sputtering.

CaZrO3 (CZO) thin films were deposited on Pt/Ti/SiO2/Si substrates at 450 °C by radio-frequency magnetron sputtering technology. The microstructures and dielectric properties of CZO thin films were investigated. X-ray diffraction analysis reveals that the perovskite orthogonal CZO phase would be promoted by a higher O2 partial pressure in the flow ratio of O2/Ar after thin films were annealed at 700 °C for 3 h in air. The films prepared under the flow ratio of O2/Ar (20:40, 30:40 and 40:40) show the main perovskite crystal phase of CaZrO3 with a small amount of Ca0.2Zr0.8O1.8. The main crystal phase was Ca0.2Zr0.8O1.8 when the film was deposited under an O2/Ar ratio of 40:10. The annealed film with a 40:40 O2/Ar ratio exhibits a dielectric performance with a high dielectric constant (εr) of 25 at 1 MHz, a temperature coefficient of permittivity of not more than 122.7 ppm/°C from 0 °C to 125 °C, and a low leakage current density of about 2 × 10-7 A/cm2 at 30 V with an ohmic conduction mechanism.

Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO4 System.

Microwave dielectric ceramics with permittivity (εr) ∼ 20 play an important role in massive multiple-input multiple-output (MIMO) technology in 5G. Although fergusonite-structured materials with low dielectric loss are good candidates for 5G application, tuning the temperature coefficient of resonant frequency (TCF) remains a problem. In the present work, smaller V5+ ions (rV = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb5+ (rNb = 0.48 Å with CN = 4) in the Nd(Nb1-xVx)O4 ceramics, which, according to in situ X-ray diffraction data, lowered the fergusonite-to-scheelite phase transition (TF-S) to 400 °C for x = 0.2. The thermal expansion coefficient (αL) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < αL < + 15 ppm/°C. The abrupt change in αL, the associated negative temperature coefficient of permittivity (τε), and the minimum value of εr at TF-S resulted in a near-zero TCF ∼ (+7.8 ppm/°C) for Nd(Nb0.8V0.2)O4 (εr ∼ 18.6 and Qf ∼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τε and αL at TF-S is thus demonstrated that may also be extended to other fergusonite systems.

Stability Study of Dielectric Properties of Plasma-Sprayed BaTiO3

Barium titanate coatings were, for the first time, sprayed by a high feed-rate plasma torch with water stabilization of the plasma. Two power levels of the torch were applied for spraying to cover steel substrates. Various substrate preheating levels from 125 °C to 377 °C were used to modify cooling conditions. Microstructure and phase composition including crystallinity quantification were observed. Dielectric measurements proved that the relative permittivity between 300 and 400 coatings is too temperature sensitive over 170 °C but fits the requirements of the EIA temperature coefficient between room temperature and 170 °C. Simultaneously, the loss tangent remains rather low, between 0.02 and 0.07, in a broad range of temperatures and frequencies. Annealing was performed in air to heal the oxygen deficiency, but only modified the microstructure insignificantly. The dielectric properties of as-sprayed and annealed samples were discussed, with the main finding that the temperature coefficient of permittivity was improved by annealing. This study contributes to the search for the suitability of plasma-sprayed BaTiO3 coatings for application in the electrical industry, namely by the optimization of conditions for high feed-rate spraying.

High-temperature stability of dielectric and energy-storage properties of weakly-coupled relaxor (1-x)BaTiO3-xBi(Y1/3Ti1/2)O3 ceramics

Lead-free (1-x)BaTiO3-xBi(Y1/3Ti1/2)O3 ceramics (abbr. (1-x)BT-xBYT) were synthesized via a solid state process. X-ray diffraction (XRD) measurements and Raman spectra reveal that, for x ˃ 0.05, the ceramics structure changes from a ferroelectric tetragonal to a pseudo-cubic phase at room temperature. Dielectric tests indicate that the ceramics exhibit a relaxor behavior, the temperature (Tm) at which the maximum dielectric constant (εm) is obtained shifts towards lower values. As the BYT content increases, the dielectric dispersion factor (γ) increases from 0.99 to 1.86, the temperature coefficient of permittivity (TCϵ) decreases to ~60 ppm/°C, and the capacitance variation is within temperature coefficient of capacitance (TCC) ≤ 15% in the temperature range from RT to 400 °C (x = 0.20). Furthermore, as the BYT content increases, high polarization maxima (Pmax), low remnant polarization (Pr), and slim P-E hysteresis loops can be observed. An energy storage density (Wrec) of 1.02 J/cm3 and energy efficiency (η) of 78% were achieved for x = 0.15, while these amounted to 0.77 J/cm3 and 90% for x = 0.2. Moreover, good temperature stability of energy storage properties is also obtained. These results indicate that the as-synthesized (1-x)BT-xBYT ceramics are potential lead-free materials for energy storage applications.

Ba8CoNb6-xTaxO24 Eight-Layer Shifted Hexagonal Perovskite Ceramics with Spontaneous Ta5+ Ordering and Near-Zero τf.

Highly positive temperature coefficients of the resonant frequency (τf) of eight-layer hexagonal perovskites are hardly tunable, hindering their application as microwave dielectric resonators. Here, we show that a near-zero τf (∼0.48 ppm °C-1) can be achieved on eight-layer shifted hexagonal perovskite Ba8CoNb4Ta2O24, along with a permittivity εr of ∼30.6 and a Qf of ∼36400 GHz, through substitution of Ta for Nb, satisfying the resonator application requirement. The decrease in the τf of Ba8CoNb6-xTaxO24 takes place mainly through the decrease in the εr or temperature coefficient of permittivity, owing to the less covalent bonding and lower polarizability of Ta5+ compared to those of Nb5+. Synchrotron and neutron powder diffraction data, scanning transmission electron microscopy-high-angle annular dark field imaging, and atomic-scale X-ray energy dispersive spectroscopy elemental mapping reveal that Ta5+ cations in Ba8CoNb4Ta2O24 are naturally distributed in a partially ordered manner, showing a strong site preference on the Nb layers close to the central Co layer over the most out-of-center distorted Nb layers next to empty octahedral layers. This spontaneous Ta ordering in the niobate host is driven by different covalent bonding nature and second-order Jahn-Teller distortion extents of Ta5+ and Nb5+. The results demonstrate an effective way of substituting more ionic Ta5+ for Nb5+, which decreases the τf to near-zero values for eight-layer hexagonal perovskite niobate dielectrics.

Dielectric properties of nylon 11/CaCu&lt;inf&gt;3&lt;/inf&gt;Ti&lt;inf&gt;4&lt;/inf&gt;O&lt;inf&gt;12&lt;/inf&gt; (CCTO) nanocomposite films with high permittivity

Flexible nylon 11/CaCu 3 Ti 4 O 12 (CCTO) nanocomposite films (thickness ∼100 μm) with varying CCTO nanoceramics (0 to 30 wt%) were fabricated by solution casting method followed by vacuum drying. The nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy, and impedance analyzer to study their structural and dielectric properties. XRD analysis revealed the presence of γ-phase of nylon 11 both in as-cast film as well as in the composites. SEM micrographs indicated that the CCTO nanocrystals were distributed evenly throughout the nanocomposite films with less agglomeration. The room temperature dielectric permittivity was 168 at 50 Hz when the CCTO content increased to 30 wt% in the polymer and this was increased to 1007 at 423 K. Frequency independent dielectric behavior was observed for the frequency range of 100 kHz–10 MHz. Temperature coefficient of permittivity showed that the permittivity of the nanocomposites is highly temperature dependent.

High‐energy storage and temperature stable dielectrics properties of lead‐free BiScO 3 –BaTiO 3 – x (Bi 0.5 Na 0.5 )TiO 3 ceramics

Lead-free (1–x)(0.4BiScO3–0.6BaTiO3)-x(Bi0.5Na0.5)TiO3 (BSBT–xBNT) ceramics were prepared by traditional ceramics preparation method. The energy storage characteristics, as well as dielectric spectrum curves of BSBT–xBNT ceramics, were systematically used in research. The ternary system formed perovskite solid solution with dense and homogenous microstructure. BSBT–xBNT ceramics exhibited slimmer and slanted hysteresis loops followed by higher saturation polarisation (P max) and lower remnant polarisation (P r), which induced high-energy storage density of 1.39 J/cm3 (E = 180 kV/cm). Ranging from 200 to 400°C, BSBT–xBNT ceramics had high permittivities, and a matching dielectric loss, which exhibited flat temperature coefficients of permittivity (TCɛ). The impedance spectroscopy analysis indicated that the non-Debye relaxation mechanism existed in BSBT–xBNT ceramics. BSBT–xBNT ceramics may have potential application value for the high-temperature capacitor.

Stable colossal permittivity and low loss in (In0.5Nb0.5)0.005Ti0.995O2 + x mol% ZrTiO4 composite ceramics under DC bias voltage

In this study, (In0.5Nb0.5)0.005Ti0.995O2 + x mol% ZrTiO4 (INTO–xZT) (0 ≤ x ≤ 75) composite ceramics were fabricated using a conventional solid-state reaction method. The effects of ZrTiO4 phase on the microstructure, dielectric properties, and response to DC bias were investigated. XRD and SEM results indicated that the co-doped TiO2 and ZrTiO4 coexisted well. e′ decreased with increasing ZrTiO4 content x. For the sample with x = 20, e′ = 9940, tanδ = 0.03, and temperature coefficient of permittivity (@ 1 kHz) variation < ± 15% over the temperature range from − 60 °C to 85 °C were obtained. The grain-boundary resistance (Rgb) increased by almost two orders of magnitude in contrast to that of the sample with x = 0. Stable colossal permittivity and low loss under DC bias (500 V/cm) were observed for the sample with x = 20. These outstanding dielectric properties were attributed to the considerable improvement in Rgb and the smaller grain size of the composite ceramics with appropriate ZrTiO4 content.

Controlling the phase transition in nanocrystalline ferroelectric thin films via cation ratio.

Traditionally, the ferroelectric Curie temperature can be manipulated by chemical substitution, e.g., in Ba1-xSrxTiO3 as one of the archetypical representatives. Here, we show a novel approach to tune the ferroelectric phase transition applicable for nanostructured thin films. We demonstrate this effect in nano-grained BaTiO3 films. Based on an enhanced metastable cation solubility with Ba/Ti-ratios of 0.8 to 1.06, a significant shift of the phase transition temperature is discovered. The transition temperature increases linearly from 212 K to 350 K with increasing Ba/Ti ratio. For all Ba/Ti ratios, a completely diffused phase transition is present resulting in a negligible temperature sensitivity of the dielectric constant. Schottky defects are identified as the driving force behind the off-stoichiometry and the shift of the phase transition temperature as they locally induce lattice strain. Complementary temperature dependent Raman experiments reveal the presence of the hexagonal polymorph in addition to the perovskite phase in all cases. Interestingly, the hexagonal BaTiO3 influences the structural transformation on the Ba-rich side, while on the Ti-rich side no changes for the hexagonal polymorph at the ferroelectric transition temperature are observed. This concerted structural change of both polymorphs on the Ba-rich side causes a broad phase transition region spanning over a wide range up to 420 K including the transition temperature of 350 K obtained from dielectric measurements. These findings are promising for fine adjustment of the phase transition temperature and low temperature coefficient of permittivity.

Improved dielectric tunability of PZT/BST multilayer thin films on Ti substrates

PbZr0.2Ti0.8O3/Ba0.6Sr0.4TiO3 (PZT/BST) multilayer thin films on LaNiO3 buffered Ti substrates were fabricated by sol-gel method. Results show that there are tetragonal PZT phase and cubic BST phase in the phase structure of PZT/BST films. These films with small grain size also exhibit enhanced dielectric temperature stability and reduced leakage current density. Dielectric anomaly is found for such PZT/BST multilayers: the maximum of dielectric constant and tunability respectively reaches 501 and 41.1% (400 kV/cm) when the thickness content of BST films is 50%. The corresponding temperature coefficient of permittivity (TCP) is only 2.7 × 10−4/°C. Furthermore, dielectric constant and tunability of such PZT/BST thin films are calculated by phenomenological theory. The experimental data of dielectric constant and tunability are both in between the calculated results of without and complete electrostatic coupling, indicating that dielectric anomaly is caused by electrostatic coupling and part coupling takes place in the fabricated films.

Fabrication of Al deposited sandwich capacitor structure with CdSe/PVA dielectric thin film by spin coating technique for high power applications: synthesis and characterizations

The capacitor structures were fabricated in the configuration of Al : CdSe/PVA : Al with CdSe/PVA as an insulating dielectric layer for high power applications. The sandwiched layer gave an excellent energy density and a better dielectric strength that was obtained from the amalgamation of CdSe and poly (vinyl alcohol). For the detailed analysis of the interaction between CdSe and PVA, transparent CdSe/PVA composites were synthesized by ultra-sonication technique with micrometer thicknesses at different wt% of CdSe. The UV absorption edge of PVA matrix corresponds to π→π* transition associated with ethylene unsaturation (C=C) was analysed and it was shifted towards higher wavelength with the CdSe incorporation. The sub-band states formation was evaluated, Urbach energy was increased up to ~835 meV, and an increase in structural defect was noticed by widening the tail state within the polymer matrix with the impurity addition. Optical parameters which include extinction coefficient (k) and index of refraction (n) have been determined. Three dielectric relaxations were pronounced as α, β and interfacial polarization and the high relative permittivity and the low values of dissipation factor indicated that the dielectric phenomenon was predominant in all membranes. Inspection of electrical conduction rate to temperatures was also investigated and the temperature coefficient of capacitance and temperature coefficient of permittivity were listed. Thermal stability could be enhanced with CdSe interaction and the variation in thermal parameters was discussed.

Development of MEMS wireless wall temperature sensor for combustion studies

In this paper, a MEMS-based wireless wall temperature sensor for application to combustion studies is proposed. The resonant frequency change of an LCR circuit on the sensor is used to detect the temperature change, and is transferred by inductive coupling between the sensor and the read-out coil. Sensitivity analysis has been made to examine the effect of the resistance/capacitance change of the sensor on the resonant frequency shifts. Based on the present analysis, the sensing principle with either TCR (temperature coefficient of resistance) or TCP (temperature coefficient of permittivity) can be determined for better temperature sensitivity. The sensor configuration is designed through an equivalent circuit model, and verified with a 3D electromagnetic simulation. A prototype sensor on a glass substrate is successfully fabricated through MEMS technologies. Performance of the sensor is evaluated in the steady thermal field with the temperature range from 25 °C to 175 °C. The profile of the resonant frequency change is well fitted with a quadratic curve derived from the model analysis. The temperature measurement accuracy of 1.6 °C at 25 °C and 0.87 °C at 175 °C has been obtained at the measurement distance of 0.71 mm. In addition, a similar measurement uncertainty can be achieved with a 52 ms measurement time interval.

Electret-based Unsteady Thermal Energy Harvester using Potassium Tantalate Niobate Crystal

An electret-based unsteady thermal energy harvester is proposed using potassium tantalate niobate (KTa1-xNbxO3, KTN) as a dielectric for the capacitor. By connecting in series the capacitor and an electret serving as a permanent voltage source, the capacitance change with temperature fluctuations alters the amount of induced charges thereby produces the external current. By using KTN having extremely-large temperature coefficient of permittivity together with the CYTOP electret, the output power of 572 nJ has been obtained from one heating cycle, which corresponds to 20 times higher output power than the previous result with BaTiO3.

Temperature-independent permittivity of xBaTiO3–(1−x)(0.5Bi(Mg1/2Ti1/2)O3–0.5BiScO3) ceramics

xBaTiO3–(1−x)(0.5Bi(Mg1/2Ti1/2)O3-0.5BiScO3) or xBT–(1−x)(0.5BMT–0.5BS) (x=0.45–0.60) ceramics were prepared by using the conventional mixed oxide method. Perovskite structure with pseudo-cubic symmetry was observed in all the compositions. Dielectric measurement results indicated that all the samples showed dielectric relaxation behavior. As the content BaTiO3 was decreased from 0.60 to 0.45, temperature coefficient of permittivity (TCε) in the range of 200–400°C was improved from −706 to −152 ppm/°C, while the permittivity at 400°C was increased from 1208 to 1613. The temperature stability of permittivity was further improved by using 2mol% Ba-deficiency. It was found that lattice parameter and grain size of the 2mol% Ba-deficient ceramics were smaller than those of their corresponding stoichiometric (S) counterparts, with TCε in the range of 200–400°C to be improved noticeably. For example, TCε of the Ba-deficiency sample with x=0.45 was −75ppm/°C in the temperature range of 200–400°C and the permittivity was 1567 at 400°C. The results obtained in this work indicated that xBT–(1−x)(0.5BMT–0.5BS) ceramics are very promising candidates for high temperature capacitor applications.

Relationship between tolerance factor and temperature coefficient of permittivity of temperature-stable high permittivity BaTiO3–Bi(Me)O3 compounds

The temperature coefficient of permittivity ([Formula: see text]) of BaTiO3–Bi(Me)O3 solid solutions were investigated. It was determined that as the tolerance factor was decreased with the addition of Bi(Me)O3, the [Formula: see text] shifted from large negative values to [Formula: see text] values approaching zero. It is proposed that the different bonding nature of the dopant cation affects the magnitude and temperature stability of the permittivity. This study suggests that the relationship between tolerance factor and [Formula: see text] can be used as a guide to design new dielectric compounds exhibiting temperature-stable high permittivity characteristics, which is similar to past research on perovskite and pyrochlore-based microwave dielectrics.

Microstructure and dielectric properties of (K0.5Na0.5)NbO3–Bi(Zn2/3Nb1/3)O3 − xmol%CeO2 lead-free ceramics for high temperature capacitor applications

(K0.5Na0.5)NbO3–Bi(Zn2/3Nb1/3)O3 − xmol%CeO2 [0.97KNN–0.03BZN − xCeO2] lead-free ceramics were synthesized and the phase structure, microstructure and dielectric properties were investigated. Dielectric studies reveal that the 0.97KNN–0.03BZN − 1.0CeO2 ceramics show excellent dielectric properties at a broad usage temperature range (150–350 °C): the dielectric permittivity is near 1900 (at 10 kHz) with the capacitance variation (ΔC/C150 °C) no more than ±10 %; the temperature coefficient of permittivity (TCe) is as low as −162 ppm/°C; the corresponding dielectric loss is less than 2.5 %. These results indicate that the 0.97KNN–0.03BZN − 1.0CeO2 ceramics are promising candidates for high temperature multilayer ceramic capacitor applications.

Structures, phase transformations, and dielectric properties of Bi2(Zn1−xMgx)2/3Nb4/3O7 pyrochlore ceramics as temperature stable LTCC material

As a candidate of thermostable LTCC material, Bi2(Zn1−xMgx)2/3Nb4/3O7 (0.0⩽x⩽1.0) ceramics with improved dielectric properties have been prepared via conventional mixed oxide route. The relations of phase equilibrium, crystal structure and dielectric properties of the composites were investigated systematically. A monoclinic – [ monoclinic+cubic ] – cubic phase transition occurred with the increasing Mg2+ content. The phase boundaries located around x=0.3 and x=0.7 for monoclinic and cubic phases, respectively. Near-zero temperature coefficient of permittivity was obtained and the permittivity was improved from 80 to 200 in this system, which were strongly correlated with phase composition. The Bi2(Zn1−xMgx)2/3Nb4/3O7 ceramic with x=0.5 satisfied the EIA specification NP0 exhibited excellent dielectric properties of k′=98, tanδ=3.4×10−4, τk=0.65ppm/°C with the low-firing temperature of 900°C within the two-phase region, which can be a promising candidate for low temperature co-fired ceramics (LTCC) and multilayer components applications in high frequency and microwave range.

Changes in Permittivity and Density of Molecular Liquids under High Pressure

We collected and analyzed the density and permittivity of 57 nonpolar and dipolar molecular liquids at different temperatures (143 sets) and pressures (555 sets). No equation was found that could accurately predict the change to polar liquid permittivity by the change of its density in the range of the pressures and temperatures tested. Consequently, the influence of high hydrostatic pressure and temperature on liquid permittivity may be a more complicated process compared to density changes. The pressure and temperature coefficients of permittivity can be drastically larger than the pressure and temperature coefficients of density, indicating that pressure and particularly temperature significantly affect the structure of molecular liquids. These changes have less influence on the density change but can strongly affect the permittivity change. The clear relationship between the tangent and secant moduli of the permittivity curvatures under pressure for various molecular liquids at different temperatures was obtained, from which one can calculate the Tait equation coefficients from the experimental values of the pressure influence on the permittivity at ambient pressure.

Synthesis and characterization of indium aluminate (InAlO3) nanoparticles by wet chemical method

We have synthesized a new class of indium aluminate (InAlO3) nanoparticles at different calcinations temperatures by a very simple and cost effective wet chemical method. Composition analysis was carried out by using Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. X-ray diffraction pattern revealed that the as prepared samples have hexagonal phase with cubic traces. The samples calcined above 400°C revealed cubic phase. Scanning electron microscopy showed that the as prepared and calcined samples have rock like irregular shape agglomerates. Thermal behavior was studied by using differential scanning calorimeter. The blue emission observed in photoluminescence studies was attributed to oxygen vacancies. The dielectric constant of InAlO3 was found to be very high (≈32 at 1kHz). The dielectric loss (tanδ), temperature coefficient of capacitance (TCC), temperature coefficient of permittivity (TCP) and linear expansion coefficient (α) were found to be very low. The results obtained indicated that the synthesized InAlO3 nanoparticles could be used to prepare nano/thin films by thermal evaporation technique for the fabrication of field effect thin film transistors and opto electronic device applications in the near future.

Static permittivities of ethanol mixtures with isomers of propanol and butanol at temperatures from 288.15 to 308.15 K

The relative permittivities of five binary mixtures of ethanol with propan-2-ol, butan-1-ol, butan-2-ol, 2-methylpropan-1-ol and 2-methylpropan-2-ol are reported for twenty-one mole fractions over the entire concentration range at 288.15, 293.15, 298.15, 303.15 and308.15 K. The excess static permittivity, the permittivity temperature coefficient (∂lnε r/∂T) and its excess values were calculated. The excess parameters were fitted to the Redlich–Kister polynomial equation. The results were used in the analysis of hydrogen-bond inter molecular interactions occurring in the alcoholic binary mixtures having different natures of their constituents with varying carbon chain lengths.