Temperature Dependence Of Dielectric Permittivity Research Articles

Antiferroelectricity of titanite-type oxide SrTiGeO5 and its potential for power electronics applications

Antiferroelectric materials have recently received renewed attention due to the increased demand for energy-storage ceramics and power electronics applications. This study demonstrates antiferroelectricity in a titanite-type oxide, SrTiGeO5, through direct observation of a double D-E hysteresis loop by polarization measurements. Temperature dependence of dielectric permittivity shows a cusp around 550 K, indicating a relatively high antiferroelectric phase transition temperature for SrTiGeO5. It is suggested that an electric-field-induced rise of permittivity in SrTiGeO5 has the potential for application in protective circuits of power electronics devices. The present study paves the way for the development of innovative antiferroelectric applications.

Synthesis and Characterization of the Electrical and Energy Storage Properties of New Barium Titanate - Europium Titanate Solid Solution

In the present work, the investigation of the structural, dielectric, ferroelectric and energy storage properties of polycrystalline samples of (1-x)BaTiO3 – xEuTiO3 (BT-ET) solid solution materials prepared by conventional solid-state reaction method has been carried out. X-ray diffraction analyses have revealed the formation of a single-phase tetragonal structure with the P4mm space group. Furthermore, the temperature dependence of the dielectric constants marked the presence of the following sequence of structural phase transitions, namely from rhombohedral to orthorhombic, from orthorhombic to tetragonal and from tetragonal to cubic phase transitions with the increase of temperature. A diffuse phase transition has been observed from the dielectric permittivity peak and has been analyzed using the modified Curie-Weiss law and the degree of diffuseness is found to be in the range of 1.16 - 1.76 due to the existence of different states of polarization. A phase diagram has been established based on the temperature-dependent dielectric permittivity studies. The room temperature ferroelectric properties point to a coercive field larger than that of BaTiO3 ceramics. Broad dielectric peaks associated with diffuse phase transition appear in a wide temperature range (40 - 100 °C) with the highest dielectric permittivity ε’ = 6498 found in the x = 0.05 ceramics. Moreover, an improved energy storage performance is obtained in the 0.95BaTiO3-0.05EuTiO3 ceramic with a recoverable energy density of Wrec = 0.797 J/cm3, coupled with an efficiency η = 73% at 170 kV/cm and the highest storage energy density of Wst = 1.571 J/cm3 is obtained for 0.90BaTiO3-0.10EuTiO3, which is superior to other lead-free BT-based ceramics. All these features demonstrate that the BT-ET ceramics can be widely used in energy storage applications and also in high-temperature multilayer capacitors for automotive, aerospace and related industries.

Growth, Structure, and Electrical Properties of AgNbO3 Antiferroelectric Single Crystal

AgNbO3 (AN) lead-free antiferroelectric material has attracted great attention in recent years. However, little focus has been directed toward a single crystal that can provide more basic information. In this study, we successfully grew high-quality AN single crystals, using a flux method, with dimensions of 5 × 5 × 3 mm3. A systematic investigation into the crystal structure, domain structure, and electrical properties of a [001]-oriented AN single crystal was conducted. X-ray diffraction and domain structure analysis revealed an orthorhombic phase structure at room temperature. Stripe-like 90° domains aligning parallel to the [110] direction with a thickness of approximately 10–20 μm were observed using a polarized light microscope. The temperature dependence of dielectric permittivity showed M1-M2, M2-M3, and M3-O phase transitions along with increasing temperature, but the phase transition temperatures were slightly higher than those of ceramic. The AN single crystal also exhibited double polarization-electric field (P-E) hysteresis loops, which enabled good recoverable energy-storage density and efficiency comparable to ceramic. Additionally, double P-E loops were kept stable at various temperatures and frequencies, demonstrating robust stability and confirming typical antiferroelectric characteristics. Our work provides valuable insights into understanding the fundamental antiferroelectric properties of AN-based materials.

Dielectric and FTIR Investigation of the Cholesteric Liquid Crystal with the Doping of the Polymer

AbstractThe present work investigates fluorescent polymer dispersion in the cholesteric liquid crystal (LC) as a function of temperature and concentration of polymer. The dielectric parameters of the cholesteric LC are determined by measuring capacitance and inductance with the function of the frequency and temperature. The material used for doping is a polymer‐poly[(4,4′‐hexafluoroisopropylidene) diphthalic anhydride‐alt‐3,6‐diaminoacridine hemisulfate] and it is one concentration doped in pure cholesteryl stearate. The temperature dependence of dielectric permittivity has been discussed for the pure and polymer‐doped system. In addition to this Fourier transform infra‐red (FTIR) spectroscopy has also been performed to understand the interaction between cholesteric LC and polymer molecules.

Terahertz dielectric properties of Fe3O4 thin films deposited on Si (100) substrate

Fe3O4 is considered to be a promising material for terahertz spintronic applications as well as for stealth technology. However, the optical properties of Fe3O4 in the thin film form at terahertz frequencies are not reported in literature. In this article, we present the frequency and temperature dependence of dielectric permittivity (ε 1) and optical conductivity (σ 1) of Fe3O4 films deposited on Si substrate. The σ 1 of these films show absorption peaks related to charge localization and shallow impurities. It is also observed that the Fe2O3/Fe3O4 composite films have large σ 1 and ε 1 indicating their potential use for stealth technology applications. The overall optical properties are found to depend strongly on the microstructure and defects, such as, the grain size and the presence of grain boundaries, anti-phase boundaries, strain disorder due to lattice mismatch and/or the Fe+2/Fe+3 ratio.

Magnetic and electrical transport properties of Cu0.5Ni0.5Fe2O4 ferrite synthesized by plasma arc discharge process

In this study, the plasma arc discharge process was employed to synthesize nanocrystalline Cu0.5Ni0.5Fe2O4 ferrite powders. A spinel-type ferrite structure has been formed successfully, exhibiting a saturation magnetization of 87 emu g−1 and a coercivity of 26 Oe. The investigation involved studying the frequency and temperature dependence of dielectric permittivity, dielectric loss, and DC/AC conductivity over a broad frequency range (1 kHz–1 MHz) in a temperature range of 298 K–403 K. The highest value of the dielectric contestant (4746) is observed at a frequency of 1 kHz and temperature of 313 K. A maximum in the DC conductivity is observed at 403 K, which can be ascribed to the combined effects of thermally activated hopping and an increase in the concentration of both n-type and p-type charge carriers at higher temperatures.

Temperature-dependent complex dielectric permittivity: a simple measurement strategy for liquid-phase samples

Microwaves (MWs) are an emerging technology for intensified and electrified chemical manufacturing. MW heating is intimately linked to a material’s dielectric permittivity. These properties are highly dependent on temperature and pressure, but such datasets are not readily available due to the limited accessibility of the current methodologies to process-oriented laboratories. We introduce a simple, benchtop approach for producing these datasets near the 2.45 GHz industrial, medical, and scientific (ISM) frequency for liquid samples. By building upon a previously-demonstrated bireentrant microwave measurement cavity, we introduce larger pressure- and temperature-capable vials to deduce temperature-dependent permittivity quickly and accurately for vapor pressures up to 7 bar. Our methodology is validated using literature data, demonstrating broad applicability for materials with dielectric constant ε' ranging from 1 to 100. We provide new permittivity data for water, organic solvents, and hydrochloric acid solutions. Finally, we provide simple fits to our data for easy use.

A New Relaxor Ferroelectrics Ba4SrBiTi3Nb7O30 with Tungsten Bronze Structure

This paper reports the synthesis, microstructure and electrical properties of a new Ba4SrBiTi3Nb7O30 ceramic. X-ray diffraction analysis shows that the sample crystallizes into tungsten bronze structure, and the space group is P4bm. The electrical measurement results show that Ba4SrBiTi3Nb7O30 exhibits good dielectric and ferroelectric properties. The temperature-dependent dielectric permittivity indicates that the transition temperature of the prepared Ba4SrBiTi3Nb7O30 sample is around Tm ≈ 250K. With increasing the frequency, the dielectric peak moves to a lower temperature. Below 250 K, obvious polarization current can be detected, corresponding to the formation of spontaneous ferroelectric polarization. These results indicate the relaxor ferroelectric behavior of Ba4SrBiTi3Nb7O30 ceramic.

Temperature-dependent microwave dielectric permittivity of gallium oxide: A deep potential molecular dynamics study

The microwave (MW) dielectric permittivity of gallium oxide (β-Ga2O3) fundamentally determines its interaction with an electromagnetic wave in bulk power. Yet, there is a lack of experimental data due to limitations of high-temperature MW dielectric measurements and the large uncertainty under variable-temperature conditions. Herein, we develop a deep potential (DP) based on density functional theory (DFT) results and apply deep potential molecular dynamics (DPMD) for accurately predicting temperature-dependent MW dielectric permittivity of β-Ga2O3. The predicted energies and forces by DP demonstrate excellent agreement with DFT results, and DPMD successfully simulates systems up to 1280 atoms with quantum precision over nanosecond scales. Overall, the real part of the MW dielectric permittivity decreases with rising frequency, but the dielectric loss increases. The MW dielectric permittivity gradually increases as the temperature increases, which is closely related to the reduced dielectric relaxation time and increased static and high-frequency dielectric constants. Besides, the oxygen vacancy defects significantly reduce the relaxation time; however, augmenting the defect concentration will cause a slight rise in relaxation time. The electron localization function analysis reveals that more free electrons and low localization of electrons produced by high defect concentrations facilitate the increased relaxation time. This study provides an alternative route to investigate the temperature-dependent MW permittivity of β-Ga2O3, which attains prime importance for its potential applications in RF and power electronics.

0.98[(Na(1–x)/2Smx/2Nb0.3TiO3)] + 0.02MnO2 Lead-free Ceramic System Design; An antiferroelectrics with Improved Relaxation Behavior

The sodium niobate-based ceramics 0.98[(Na(1−x)/2Smx/2Nb0.3TiO3)] + 0.02MnO2 acronymed NSmNT of different compositions (x = 0.05, 0.1, 0.11, 0.12, and 0.13) were prepared via solid-state reaction method. The prepared samples were characterized by XRD to study the phase structure of the designed systems, SEM to study the microstructure properties of the NSmNT ceramics. In addition to that LCR meter was used to measure the sample temperature-dependent dielectric permittivity, dielectric loss, and systems impedance. The results showed an increment in the dielectric breakdown strength (DBS) with increasing x content from 100 kVcm–1 to 450 kVcm–1. Similarly, the high recoverable energy density (Wrec) of 5.61 J cm–3 was obtained for x = 0.11 symbolized (NSmNT2) with an exquisite efficiency of 88%. The study also analyzed the complex impedance of the NSmNT2 ceramics system to clearly understand the dielectric behavior of the system in question. A general view of things considers the NSmNT2 ceramic system to be a reliable system for pulsed power applications.

Temperature and magnetic field controlled dielectric relaxation and magnetodielectric response in KBiFe1.9Co0.1O5 polycrystalline

Abstract Cobalt (Co) substituted brownmillerite KBiFe2O5 (KBiFe1.9Co0.1O5: KBFCO) is synthesized by conventional solid-state reaction route. Rietveld refinement of X-ray diffraction data confirms the pure phase of KBFCO and crystallizes in monoclinic structure with P2/c space group. Surface morphology reveals that the grains are randomly distributed, and the average grain size varies in the range of 1–4 μm. The energy dispersive X-ray spectroscopy confirms that the chemical constituents of KBFCO are very close to the molar (1:1:2) ratio. The temperature (10–300 K) and frequency (500 Hz–1 MHz) dependent dielectric permittivity value decreases approximately 50% in the presence of the magnetic field (1.3 T). It confirms the signature of the magnetodielectric (MD) effect in the KBFCO sample. The magnetic field (±1.3 T) variation MD loop resembles the inverse-butterfly type behavior for the system. Both MD hysteresis and strength decrease with a decrease in temperature. A noticeable suppression in the dielectric relaxation is obtained by applying a 1.3 T magnetic field in the temperature range of 250 K–300 K. The measured MD effect is observed at a high frequency (30 kHz), suggesting the intrinsic effect is dominated in the probing temperature range. Observation of similar trends in magnetic field-dependent MD and magnetic loss (ML) loop rules out the existence of magnetoresistance origin MD effect. These results confirm that KBFCO has an excellent MD response even for a small applied field and holds great interest for future device applications.

Large negative electrocaloric response induced by nanoscale phase transition in (Bi, Na)TiO3-based thin films

Electrocaloric effect (ECE) offers an efficient and environmentally friendly route for solid-state cooling. Either positive or negative ECE could exhibit a large adiabatic temperature change (ΔT). Compared to the positive electrocaloric response, the investigation of negative ECE is lagging behind, largely due to the fact that its origin is still elusive. In this work, the negative ECE behavior of conventional ferroelectric thin films, namely 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 (BNBT), was studied. A remarkable ΔT of −26.1 K was acquired near 160 °C under a moderate electric field of 875 kV/cm, attributing to the ferroelectric phase transition in the polar nanoregions from rhombohedral (R3c) to tetragonal (P4bm), as confirmed by temperature-dependent dielectric permittivity, Raman spectra, and x-ray reciprocal space mapping. The BNBT thin film presents a high electrocaloric coefficient (ΔT/ΔE) of 0.0298 K cm kV−1, transcending that of the most reported negative electrocaloric response of thin films.

Enhancement in the magneto-dielectric and ferroelectric properties of BaTiO3 – CoFe1.9Yb0.1O4 core-shell multiferroic nanocomposite

Herein we report the dielectric, ferroelectric, magnetocapacitance and energy storage density properties of CoYb0.1Fe1.9O4-BaTiO3 core-shell multiferroic nano-composite synthesized by the combination of co-precipitation and sol-gel method. The XRD spectra revealed that the ferroelectric BT phase is compatible with the magnetic YbCFO phase. Scanning Electron microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDS) and Transmission Electron Microscopy (TEM) confirmed the formation of core-shell like structure in the composite. The magnetic and ferroelectric phase preserves their basic individual properties in the core–shell form. The temperature dependence of dielectric permittivity showed a sharp phase transition from cubic to tetragonal structure of the core-shell composite at 312.726 K. Frequency dependent dielectric study shows an enhanced value of permittivity (36905.0218) along with low dielectric losses (1.354). It was found that the prepared composite exhibited moderate values of saturation magnetization (3.379 emu/g) and polarization (5.146 μC/cm2) along with low remnant polarization (1.777 μC/cm2) at room temperature. Moreover, we also observed enhanced energy storage efficiency (60%) and magneto-capacitance (5.853%) which are explained due to strong interfacial coupling and reduced leakage current, making this composite promising for multifunctional device applications.

Re-entrant transitions of locally stiff RNA chains in the presence of polycations leads to gelated architectures.

The liquid-liquid phase separation of protein and nucleic acid mixtures drives the formation of numerous membraneless compartments in cells. Temperature variation is commonly used for mapping condensate phase diagrams, which often display unique upper critical temperatures. Recent report on peptide-RNA mixtures has shown the existence of lower and upper critical solution temperatures, highlighting the importance of temperature-dependent solvent and ion-mediated forces. In the present work, we employ residue-level coarse-grained models of RNA and polycation peptide chains for simulating temperature-induced re-entrant transitions and shedding light on the role played by mobile ions, temperature-dependent dielectric permittivity, and local chain stiffness. We show that differences in bending rigidity can significantly modulate condensate topology leading to the formation of gelated or fibril like architectures. The study also finds that temperature dependence of water permittivity is generally sufficient for recapitulating experimentally observed closed loop and LCST phase diagrams of highly charged protein-RNA mixtures. However, we find that similar-looking closed-loop phase diagrams can correspond to vastly different condensate topologies.

Effect of Sm and Fe co-doping on structural, dielectric and magnetic properties of YCrO3 perovskite

In this report, impact of co-doping of samarium (Sm3+) and iron (Fe3+) on structural, dielectric and magnetic properties of YCrO3 compound has been investigated. Here, YCrO3 and Y1-xSmxCr1-yFeyO3 (x = 0.3, y = 0.1) compounds are synthesized successfully through sol–gel auto combustion route. The synthesized samples are characterized through X-ray diffraction (XRD), surface electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), impedance analyzer and vibrating sample magnetometer (VSM) techniques. Rietveld refinement of XRD analysis reveals that both the compounds are crystallized in distorted orthorhombic structure belongs to Pnma space group. It is observed that with co-doping of both Sm3+ and Fe3+, lattice unit cell volume increases. SEM micrograph shows that the grains are slightly elongated as compared to the undoped sample. The temperature variation of real part of dielectric permittivity (εr) and tangent loss (tan δ) are analyzed over a frequency range 40 KHz − 500 KHz at a temperature range 300 K − 523 K. The temperature dependent dielectric permittivity reveals that both εr and tan δ decrease with co-doping. Moreover, both the compounds show relaxor like ferroelectric transition. Room temperature field dependent magnetization analysis shows that maximum magnetization value increases with co-doping. The result reveals that the enhanced properties with co-doping can be useful for practical device applications.

Dielectric Relaxation and Electric Conductivity of Polyethylene Doped with Barium Titanate Particles

The frequency and temperature dependences of dielectric permittivity and electric conductivity of high-density polyethylene with the additive of monodisperse barium titanate particles are studied. It was shown that dielectric permittivity and electric conductance increase with increasing of filler concentration at all temperatures. In this case, conductivity has hopping mechanizm described by the Josher theory. The corresponding exponent parameter and activation energy decrease as well as conductivity rises with increasing of barium titanate concentration. The experimental data of dielectric permittivity are compared with the Maxwell-Garnett and Bruggeman theories.

Absence of presumed ferroelectricity in methylammonium lead chloride single crystals representing organic-inorganic hybrid perovskites

The performance of organic-inorganic metal halide perovskites as photovoltaics has been exceptional over the last decade, which is attributed to their unique properties like high absorption coefficient, tunable band gap, high conversion efficiency and a lot more. It is believed that the presence of ferroelectricity in the system assists charge separation leading to an increase in their efficiency. Many researchers have also claimed them to be ferroelectrics. However, there is debate among the researchers about their structures at different temperatures which questions their polar or non-polar nature and hence the presence of ferroelectricity in them. In the present study, this controversy over ferroelectric behavior of hybrid perovskites has been addressed, on MAPbCl3 single crystals. Through temperature dependent x-ray diffraction, Raman spectroscopy, dielectric permittivity, P-E (Polarization versus electric field) and PUND (Positive up negative down) measurements, it has been shown that the organic inorganic metal halide sample, MAPbCl3, is not ferroelectric and the structure is non-polar in the entire studied temperature range. These results will help in resolving the controversy present in the existing literature regarding the ferroelectric nature of organic inorganic metal halide perovskites MAPbX3 with X as Cl, Br or I.

Optical properties, dielectric relaxor behavior, impedance and modulus spectroscopy of 0.8BiFeO3-0.2CaTiO3 composite

0.8BiFeO3-0.2CaTiO3 (0.8BFO-0.2CTO) was synthesized by the sol-gel route. Structural characterization was performed by X-ray diffraction which confirms the rhombohedral structure. FESEM analysis reveals the irregular grains that are inhomogenous and slightly dense. Temperature-dependent dielectric permittivity shows a dielectric anomaly near the magnetic phase transition temperature (TN) of BiFeO3 as well as relaxor-type ferroelectric properties. The PE loop confirms the presence of ferroelectricity in the sample. Frequency-dependent ac conductivity exhibits low frequency dispersion and was well explained by Jonscher power law. The obtained fitting parameters A (pre-exponential factor that indicates polarizability) and n (dimensionless frequency exponent) show maxima and minima at the transition temperature. The electrical properties were further analysed by impedance and modulus spectroscopy. According to these analysis, the relaxation time was distributed and does not follow the Debye type behaviour. Nyquist plots had been used to estimate grain and grain boundary contributions. A typical negative temperature coefficient of resistance (NTCR) behaviour was apparent due to the decrement in bulk and grain boundary resistances as the temperature increases. The temperature-dependent relaxation time revealed Arrhenius's behaviour. 0.8BFO-0.2CTO exhibits absorption and shows a transmittance of 40–44% in the visible region of spectra. The obtained value of Eg was ∼2.26 eV, which implies the application in ultrafast optoelectronic devices. The good ability of absorption in visible region, high transmittance, the increase of extinction coefficient with wavelength, and low band gap makes 0.8BFO-0.2CTO an extraordinary material for optical devices application. The sample also shows a decrease in magneto-capacitance and increase in magneto-impedance which reflects the presence of strong magneto dielectric coupling in 0.8BFO-0.2CTO at room temperature.

Ultrahigh strain in textured BCZT-based lead-free ceramics with CuO sintering agent

• CuO as a sintering agent lowers the sintering temperature of 125 °C, and maintains BCZT-1.0 at a high texture degree of ∼99%. • CuO-based liquid phases eliminate boundaries between templates and matrix powders, release local stress, decrease grain sizes, and increase dielectric dispersion coefficient. • Maximum strain s max of 0.38% and low h s of 5.2% along with homogeneous d 33 ∼780 pC/N and large d 33 * ∼2950 pm/V was obtained in textured BCZT-1.0. Textured BaTiO 3 (BT)-based lead-free ceramics have gained significant attention due to their high piezoelectric coefficient ( d ) and very large field induced strain ( S ). However, costly nano-size raw materials, excessively high sintering temperature and low Curie temperature ( T c ) hinder their device applications. In this work, highly [001] c -oriented (Ba 0.95 Ca 0.05 )(Zr 0.04 Ti 0.96 )O 3 ceramics with x mol% CuO ( x = 0.25, 0.5, 1.0, 2.5) denoted as BCZT- x were synthesized by templated grain growth using micro-sized raw powders. The introduction of CuO sintering agent lowered the sintering temperature by 125 °C to 1450 °C, and the BCZT-1.0 achieved a high texture degree of ∼99%. In addition, the CuO-based liquid phases eliminated boundaries between BT templates and BCZT matrix powders. Such liquid-phase sintering reduced sintering stresses, decreased the average grain size of BCZT-1.0 from 16 μm down to 13 μm, and increased the dielectric dispersion coefficient γ to 1.63. The almost smoothed out T O-T anomaly in the temperature dependence of dielectric permittivity and comparably high T c (> 102 °C) lead to better temperature stability. The narrower grain orientation distribution with full width at half maximum (FWHM) of ∼5.9° and smaller domains with the size of 0.1–0.5 μm in width and 3–8 μm in length were obtained, a high field induced maximum strain S max of 0.38% and low H s of 5.2% have been achieved in BCZT-1.0 textured ceramics together with a high and homogeneous piezoelectric stress coefficient d 33 ∼780 pC/N and very large d 33 * ∼2950 pm/V.

Correlations between electrocaloric effect and dielectric diffuseness of lead-free Ba(Ti1-Sn )O3 ceramics

This paper reported the correlations between electrocaloric effect (ECE) and dielectric diffuseness of Ba(Ti1-xSnx)O3 (abbreviated as BT-100xSn) ceramics. The BT-100xSn with pure perovskite structure has been synthesized by conventional solid-state reaction method. The temperature dependence of dielectric permittivity indicates that all the BT-100xSn ceramics are normal ferroelectric with diffused phase transition, and the dielectric diffuseness is strengthened as the Sn contents increase. The maximum ECE takes place in the vicinity of phase transition point, which is the characteristic of normal ferroelectrics. The BT-8Sn indicates the largest ∆T = 0.46 K and ∆T/∆E = 0.30 × 10−6 K m/V. The substitutions of Sn contents adjust the maximum ECE to different temperatures, and the good temperature-modulation of ECE is beneficial for the realization of ECE application. Considering the correlations between ECE and dielectric diffuseness, the experimental results demonstrate that the stronger dielectric diffuseness leads to the strengthened temperature stabilities of ECE but accompanied with decreased maximum ECE.