Loss Tan Research Articles

Performance of PVC/SiO2 nanocomposites under thermal ageing

Accelerated thermal ageing test on nanocomposites of polyvinyl chloride (PVC/SiO2) is conducted at constant temperatures of 110 °C and 140 °C. Accordingly, different PVC/SiO2 nanocomposite samples with different silicon dioxide (SiO2) filler loading are prepared. The preparation of the samples was carried out based on the solution casting technique. The loading concentrations of SiO2 in the investigating samples are 0, 1, 2.5, 5 and 7.5 wt%. The breakdown strength of the prepared PVC/SiO2 nanocomposite samples is evaluated before and after the thermal ageing test. The evaluation of breakdown strength is carried out based on American Society for Testing and Materials (ASTM) standard. Also, dielectric spectroscopy, which includes dielectric constant (έ) and tangent loss (tan δ) of nanocomposite, is performed before and after the thermal ageing test. Also, the mass losses during thermal ageing of all samples are evaluated. The results show that the breakdown strength, tan δ, and the dielectric constant (έ) of pure PVC and PVC/SiO2 nanocomposites are significantly affected by the thermal ageing test. Adding a small amount of SiO2 nanoparticles to PVC leads to improvement in its dielectric properties before and after the thermal ageing process as compared to the pure PVC. The mass loss of PVC/SiO2 nanocomposite during thermal ageing is less than that of pure PVC and confirms the obtained result from breakdown strength.

The Influence of Technological Conditions on Dielectric and Optical Properties of K0.5Bi0.5TiO3 Ceramics

Lead-free ceramics of potassium-bismuth titanate K0.5Bi0.5TiO3 were obtained by a conventional sintering method under various technological conditions. The dielectric permittivity (ε) and dielectric loss (tan(δ)) measurements for these ceramics were carried out in the temperature range from 293 K to 873 K with the frequency range from 0.1 kHz to 2 MHz. An increase in dielectric permittivity with an increasing sintering temperature was observed. For the sample obtained at 1313 K and a 3.5-hour sintering time, the value of ε was about 4.55·103 (f = 100 kHz) which is twice higher than the value of ε for the sample obtained at a temperature of 1298 K and a 7-hours sintering time. For all samples, the maximum value of dielectric permittivity was shifted towards higher temperatures with an increasing frequency, which is a characteristic features of ferroelectric relaxor materials. The dielectric properties of all materials were very similar, especially in the case of dielectric loss. The values of tan(δ) at room temperature varied from about 0.07 at 0.1 kHz to 0.1 at 2 MHz. The Raman studies were performed at room temperature. No significant changes were observed for different sintering temperatures and times for all samples. The presented material can be a starting point for the development of new ferroelectric relaxor materials.

Влияние химического состава кристаллов TlIn-=SUB=-1-x-=/SUB=-Er-=SUB=-x-=/SUB=-S-=SUB=-2-=/SUB=- (0≤ x≤0.01) на их диэлектрические характеристики и параметры локализованных состояний

The frequency dependences of the real (ε) and imaginary (ε ″) components of the complex dielectric constant, tangent of dielectric loss (tan) and ac conductivity (σac) of the obtained TlIn1-хErхS2 (0  x  0.01) crystals have been studied in the frequency range f = 5104–3.5107 Hz. It is established that in TlIn1-хErхS2 a relaxation dispersion of ε and ε″ takes place. The effect of erbium concentration (Er) in TlIn1-хErхS2 crystals on their dielectric coefficients was studied. In the high frequency range, the ac conductivity of TlIn1-хErхS2 crystals obeyed the σac ~ f 0.8 law, which is characteristic of a hopping charge transfer mechanism at states localized near the Fermi level. The parameters of states localized in the band gap and the influence of the chemical composition of the TlIn1-хErхS2 crystals on these parameters are estimated.

Synthesis, structural, optical and electrical properties of La-modified Lead Iron Titanate ceramics for NTCR thermo-resistance based sensors

Abstract A La-modified Lead Iron Titanate (Pb1−xLax)(Fe0.01Ti0.99)O3 (x = 0, 4, 8, 12, 16 and 20%) (Lx-LITO) ceramics have been synthesized by sol-gel route. The structural properties of these compounds have been examined by XRD and Raman spectroscopy. The Optical properties of Lx-LITO have been investigated by UV- visible spectroscopy to evaluate their optical band gap (Eg). Moreover, we have studied in details the effect of dopant content (x%) on the structural and dielectric properties at a large range of temperature up to 600 °C and frequency 100 Hz-1MHz. At room temperature, Lx-LITO have relatively high real permittivity (eʹ) which increases from 250 to 850 with rising x% and insignificant dielectric losses (tan(δ) 16% at room-temperature thermistor applications. The effect of dopant content (x%) on NTC parameters is discussed and appears to be promising material for NTCR applications.

Dynamic mechanical behavior of flocked layer composite materials

A custom designed dynamic mechanical apparatus was constructed to measure the tan(δ) (loss tangent) properties of Flocked (layer) Energy Absorbing Materials (FEAM). Flocked Impact Energy Absorbing (IEA) materials derive their dynamic mechanical impact absorbing properties from the compressional deformation (bending, buckling) and inter-fiber friction of nominally upright flocked fibers in the flock fiber composite assembly. The reported work summarizes the dynamic mechanical, low strain, linear viscoelastic tan(δ) properties of FEAM composite layer structures at frequencies from 25 to 100 Hz and a temperature range of 0 °C–50 °C. The effect of tan(δ) at various flock densities (fibers/mm2) was also measured. These studies were carried out to gain information and insight into the role that a material’s dynamic mechanical properties have on the overall IEA performance of sport (and military) apparel pad structures. Results show that the tan(δ) of FEAM materials increases as the measuring frequency and flocked layer’s flock density increase. Tan(δ)’s behavior at various temperatures (0 °C–50 °C) did not follow an expected trend; the highest tan(δ) value was observed to occur at room temperature. Nevertheless, the obtained tan(δ) information on these various FEAM configurations should provide some guidance in designing optimized FEAM sport (and military) pad IEA composites.

Dielectric spectroscopy of Ag-starch nanocomposite films

In the present work Ag-starch nanocomposite films were fabricated via chemical reduction route. The formation of Ag nanoparticles was confirmed using transmission electron microscopy (TEM). Further the effect of varying concentration of Ag nanoparticles on the dielectric properties of starch has been studied. The frequency response of dielectric constant (ε′), dielectric loss (ε″) and dissipation factor tan(δ) has been studied in the frequency range of 100 Hz to 1 MHz. Dielectric data was further analysed using Cole-Cole plots. The dielectric constant of starch was found to be 4.4 which decreased to 2.35 in Ag-starch nanocomposite film containing 0.50 wt% of Ag nanoparticles. Such nanocomposites with low dielectric constant have potential applications in microelectronic technologies.

Magneto-induced polarization enhancement and magneto-dielectric properties in oxygen deficient La0.67Sr0.33MnO3-/BaTiO3 composite film

Magnetoelectric composite film is an important type of multiferroic materials, which is usually composed of typical ferromagnetic and ferroelectric materials. For the ferroelectric layer, BaTiO3 (BTO) attracts much attention due to its lead-free characteristic. For the ferromagnetic layer, doped manganite (R1-xAxMnO3) has been a good candidate for designing the advanced multiferroic films. Multiple interactions among the freedom degrees of charge, orbital, spin and lattice inside the doped manganite bring many additional properties into the manganite based composite films. At present, most of researches of manganite/BTO focus on the stoichiometric oxygen ion in manganite. Considering the fact that the oxygen deficiency can remarkably adjust the properties of manganite itself and relevant heterostructure by the interface effect, abnormal magnetoelectric properties are expected in an oxygen deficient manganite/BTO composite film. In this work, a composite film composed of BTO and oxygen deficient La0.67Sr0.33MnO3- (LSMO) is deposited on LaAlO3 001 substrate by the pulsed laser deposition method, and the effects of magnetic field on the properties of polarization and dielectric in a temperature range of 20-300 K are investigated. The X-ray diffraction pattern reveals good epitaxial growth of this bilayer film. The upper LSMO film exhibits semiconductive characteristic (dR/dT 0) in a temperature range of 20-300 K. Magnetization curves indicate that the LSMO keeps ferromagnetic state without any magnetic phase transition in this temperature range. When applying a magnetic fields of 0.8 T, the resistance in LSMO is observed to decrease. The changing rate MR=|R0.8 T-R0 T|/R0 T decreases from 45.28% at 30 K to 0.15% at 300 K. This composite film exhibits remarkable temperature-dependent magneto-induced ferroelectric and dielectric change. It is found that the remanent polarization (Pr) and coercive electric field (Ec) are enhanced by the 0.8 T magnetic field. The maximum changing rates of Pr and Ec are 111.9% and 89.6% at the temperatures of 40 K and 60 K, respectively. The magnetic field enhances the dielectric constant , but suppresses the dielectric loss tan . The maximum changing rates of and tan both occur at 60 K with the values of 300% and 50.9%. The temperature at which appear the maximum magneto-induced relative changes of polarization and dielectric parameters is accordant with the temperature at which occurs the peak value of magnetoresistance, which indicates a charge-based coupling in this heterojunction. A potential mechanism is that the magnetic field promotes the degree of parallelism of local spin magnetic moment of Mn ion, and produces an indirect effect on BTO layer by the spin-obital coupling and interface effect. Our findings make the oxygen deficient LSMO/BTO heterojunction promising for the design of multiferroic devices.

Structural and impedance spectroscopy characteristics of BaCO3/BaSnO3/SnO2 nanocomposite: observation of a non-monotonic relaxation behavior.

A BaCO3/BaSnO3/SnO2 nanocomposite has been prepared using a co-precipitation method without adding any additives. The prepared sample was characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. Detailed studies on the dielectric and electrical behavior (dielectric constant, complex impedance Z*, ac conductivity, and relaxation mechanisms) of the nanocomposite have been performed using the nondestructive complex impedance spectroscopy technique within the temperature range 150–400 K. The dielectric constant of the sample as a function of temperature showed the typical characteristics of a relaxor. The maximum dielectric constant value was observed to depend on frequency. The non-monotonic relaxation behavior of the prepared nanocomposite was evidenced from the spectra of loss tan, tan(δ). The relaxation kinetics was modeled using a non-Arrhenius model.

Role of ytterbium on structural and magnetic properties of NiCr0.1Fe1.9O4 co-precipitated ferrites

Ytterbium (Yb) doped NiCr0.1YbxFe1.9−xO4 (x = 0.00, 0.002, 0.04, 0.06, 0.08) spinel ferrites with different crystallite sizes have been prepared by co-precipitation technique and their magnetic and dielectric properties were investigated. X-ray diffraction data suggested that, after doping, all the samples possess a main spinel phase along with few traces of YbFeO3 (secondary phase). The addition of Yb3+ resulted in a decrease of crystallite size and an increase in X-ray density. The magnetic measurements indicated that saturation magnetization (Ms), coercivity (Hc) and remanence (Mr) of all the samples decreased by increasing dopant (Yb) concentration. Dielectric constant, dielectric loss and tan loss were also minimized with the increase in frequency as well as increase in the concentration of Yb3+ ions in the nickel chromium based spinel ferrites. AC conductivity was directly proportional to frequency and inversely proportional to concentration of Yb3+ ions. These ytterbium doped nickel ferrites may be potential candidates for the fabrication and development of high frequency switching devices.

Effect of heat in chitosan dissolution and addition of KI on the enhancement of ionic conductivity

This work focuses on the effect of chitosan-based carbohydrate polymer electrolytes (CHPE) that were prepared by the application of heat in chitosan dissolution. Furthermore, various wt% of potassium iodide (KI) that was incorporated into this heat-applied chitosan (KI-HAC) were investigated. Electrochemical impedance spectroscopy (EIS) shows that the pure HAC has the room temperature ionic conductivity of 5.57 × 10−4 S/cm. The conductivity enhanced from 5.57 × 10−4 S/cm to 6.39 × 10−4 S/cm on the addition of 0.3 wt% of KI and further enhanced to 2.07 × 10−2 S/cm on the increment of KI from 0.3 to 1.8 wt%. The conductivity enhancement in chitosan was found due to the formation of amino glucosyl carboxonium ions (AGCI) and is due to the effect of heat in chitosan dissolution. XRD affirms the reduction in crystallinity. SEM analysis shows the spherical morphology for pure chitosan, porous morphology for HAC, and KI-HAC. FTIR confirms the degradation of chitosan and the formation of AGCI. Dielectric study, dielectric tan loss study, and dielectric modulus study confirm the results obtained by EIS. The results are authenticating that the conductivity enhancement in CHPE is not only due the addition of inorganic salt but also due to the chitosan which plays the role in conductivity enhancement. Dye-sensitized solar cell using HAC and KI-HAC shows efficiency of 1.25 and 1.62% at 1 sun condition.

Low-loss Z-type barium hexaferrite composites from nanoscale ZnAl2O4 addition for high-frequency applications

In this study, nanocrystalline ZnAl2O4 (ZA) were introduced to Z-type barium hexaferrite (Co2Z) and the effects of ZA addition upon the crystal-phase composition, microstructure, permeability and permittivity as well as losses characteristics over a wide frequency range of 10 MHz–1 GHz have been systematically investigated. With increasing ZA content (x) from 0 to 15 wt%, the permeability μ′ at low frequencies decreased from 12.0 to 4.3, while the permittivity ε′ was decreased from 27.4 to 10.7. Correspondingly, the frequency stability of permeability and permittivity were improved and the losses were effectively reduced. When x is in the range of 5–10 wt%, the magnetic loss tan δμ is in the order of 10-2 and the dielectric loss tan δε is in the order of 10-3 at 300 MHz, which is lower by one order of magnitude compared with that of undoped Co2Z. The modified magnetic and dielectric properties are closely related to the changing phase composition and microstructure.

Dielectric and modulus analysis of the photoabsorber Cu2SnS3

Dielectric properties of the ternary semiconductor compound Cu2SnS3 is studied for the first time in the high temperature range from 300°C to 440°C with the frequency range 1kHz to 1MHz. The dielectric constant ε′ and dielectric loss tan(δ) were observed to increase with temperature and decrease rapidly with frequency to remains constant at high frequencies. The variation of the dielectric loss Ln(ε") with Ln(ω) was found to follow the empirical law, ε"=Bωm(T). The dielectric data were analyzed using complex electrical modulus M* at various temperatures. The activation energy responsible for the relaxation is estimated from the analysis of the modulus spectra. The value of the hopping barrier potential is estimated from the dielectric loss and compared with the value previously obtained from ac-conductivity. These results are critical for understanding the behavior of based polycrystalline family of Cu2SnS3 for absorber materials in solar-cells.

Study of dielectric properties of adulterated milk concentration and freshness

The knowledge of dielectric properties may hold a potential to develop a new technique for quality evaluation of milk. The dielectric properties of water diluted cow’s milk with milk concentration from 70 percent to 100 percent stored during 36hour storage at 22°C and 144 hour at 5°C were measured at room temperature for frequencies ranging from 10 to 4500 MHz and at low, high & at microwave frequencies using X band bench and open-ended coaxial-line probe technology, along with electrical conductivity. The raw milk had the lowest dielectric constant (ϵ′) when the frequency was higher than about 20M.Hz, and had the highest loss (ϵ″) or decepation factor tan (δ) at each frequency. The penetration depth (dp) increased with decreasing frequency, water content and storage time, which was large enough to detect dielectric properties changes in milk samples and provide large scale RF pasteurization processes. The loss factor can be an indicator in predicting milk concentration and freshness.

Elucidation of structure and conduction mechanism in Nd-Mn substituted Y-type strontium hexaferrites

Technologically important ferrites magnetic materials with nominal composition “Sr2-xNdxCo2MnyFe12-yO22” (x = 0.0 to 0.1 and y = 0.0 to 1.0) were fabricated by the simple sol-gel method. The X-ray diffraction analysis endorsed the formation of well-defined Y-type hexagonal single phase with crystallite size in range of 38–45 nm. Owing to reduction of Fe3+ ions at octahedral site, an increase in DC resistivity was observed from 4.083 × 108 to 2.376 × 109 Ω-cm with the increase in substituents content. The two conduction mechanisms operating in ferri- and paramagnetic regions were shown by Arrhenius plot. It was observed that conduction in ferrimagnetic and paramagnetic regions was governed by the hopping of electrons and polarons, respectively. The decrease in Curie temperature “Tc” (553-423 K) was detected as a factor of Nd-Mn content due to decrease in FeFe interaction at octahedral site. The changes in the values of dielectric constant (ε′), dielectric loss factor (ε″) and tan loss (δ) follow Maxwell-Wagner model. The relatively high resistivity (2.376 × 109 Ω-cm) and low dielectric constants (2.97 at 1 MHz) for the sample with x = 0.1 and y = 1.0 make this material as an excellent candidates for high frequency microwave devices.

Structural and electromagnetic characterization of Co-Mn doped Ni-Sn ferrites fabricated via micro-emulsion route

Ni0.5Sn0.5CoxMnxFe2−2xO4 ferrites with x=0.0–0.8 have been prepared by the micro-emulsion method, using CTAB as a surfactant material. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and vibrational sample magnetometer (VSM) were used to investigate the effects of Co and Mn substitutions on cationic distribution, crystallite size, lattice constant, spectral, magnetic and dielectric properties. Lattice constant and crystallite size were found to increase from 7.4 to 9.25Å and from 11.8 to 19.7nm respectively with increasing substitution of Co and Mn ions. Saturation magnetization (MS) gradually increased from 20.5 to 47.6emu/g with increase in the value of x. However, Coercivity increased from 152.7 to 462.4Oe up to x=0.4 and then it decreased thereafter. The dielectric constant, complex dielectric constant and tan loss (tanδ) were observed to decrease with increase in frequency, depicting the semiconductor behavior of the ferrites. Dc resistivity was observed to decrease considerably upon addition of Co and Mn content. The outcome for the tunable magnetic properties and achieved modification of the synthesized nanocrystallites may be chosen for tremendous applications; such as miniaturized memory devices that are based on the energy storage principles and capacitive components.

The influence of Ga doping on structural magnetic and dielectric properties of NiCr0.2Fe1.8O4 spinel ferrite

A series of spinel ferrites NiCr0.2GaxFe1.8−xO4 (x=0.00, 0.002, 0.04, 0.06, 0.08) was prepared by co precipitation technique. The influence of rare earth element Ga ions the structural dielectric and magnetic properties of NiCr0.2Fe1.8O4 ferrites was investigated. The X-ray diffraction confirmed the phase precipitated out was pure spinel phase with few traces of secondary phases. The crystallite size decreases and density increases with the increases of Ga contents. The magnetic moment, saturation magnetization and remanent magnetization increased with addition of Ga ions in spinel ferrite. The dielectric constant is described that it decreases more suddenly at low frequencies as compare at higher frequencies. The decrease in dielectric loss with frequency follows Deby's relaxation phenomena. Both the variation in tan loss and dielectric loss with frequency shows a similar. AC conductivity increases with the increases of frequency which inversely proportional to concentration of Ga3+ ions follows Jonscher law. These Gallium Chromium doped nickel ferrites are very helpful for high frequency switching devices.

Cobalt substitution induced magnetodielectric enhancement in multiferroic Bi2Fe4O9

Antiferromagnetic Bi2Fe4O9 (BFO) lightly substituted by cobalt is studied for magnetodielectricity. The substitution causes a substantial decrease in the Néel temperature (TN) from 250 K (in the parent sample, BFO) to 152 K (in the 2% Co substituted sample). At the same time, the substituted samples display a pronounced irreversibility in the zero field cooled-field cooled magnetization data for T < 370 K and opening of hysteresis in the M-H plot, thus signifying the onset of weak ferromagnetism and magnetic glassiness. The induced magnetic glassiness is found to slow down the dynamics such that the magnetization decay follows M(t)∝ exp[−(t)1−p]. The dielectric measurement in the same temperature window shows the unusual oppression in ε′ for T ∼ TN and the contrasting nature of tan loss for temperatures above and below TN, thus hinting a plausible coupling between the magnetic and electric order parameters. A confirmation to this coupling is seen in the magnetodielectric (MD) results, in which it is found that the substitution induces an additional component in the MD, apart from the usual components in BFO. This additional component of MD is found to obey ∝exp (ω)n behaviour, with the “n” values being comparable to “1-p” of magnetization. The temperature variation of MD also shows a contrasting behaviour for the parent and 2% Co substituted samples with an enhancement of two times in the MD value. In summary, our study shows that magnetoelectric coupling introduced by the magnetic glassiness and its behaviour is very much different from the intrinsic one.

Obtaining and electrical properties of ceramics based on mixed niobium and tantalum pentoxide Nb2(1–y)Ta2y O5

A method is developed for the preparation of mixed pentoxide Nb2(1–y)Ta2y O5 by rapid coprecipitation of a mixture of hydroxides of niobium and tantalum from a solution of hydrofluoric acid by ammonia water, followed by purification and calcination of the precipitate. The proposed method allows obtaining a homogeneously mixed pentoxide of niobium and tantalum Nb2(1–y)Ta2y O5, in contrast to the method of obtaining Nb2(1–y)Ta2y O5 from a mechanical mixture of individual pentoxides of niobium and tantalum. The temperature dependences of the real part of the permittivity (e′) of ceramic samples of Nb2(1–y)Ta2y O5 at various frequencies were investigated and the magnitude of dielectric loss (tan(δ)) versus frequency measurement of the electric field and temperature was evaluated. On the basis of analysis of the data of impedance spectroscopy, the temperature dependence of the static conductivity σ dс of the ceramic Nb2(1–y)Ta2y O5 was determined. From the temperature dependence of σ dс , the enthalpies of activation of charge transport for different temperature ranges were evaluated.

Low-loss NiZnCo ferrite processed at low sintering temperature with matching permeability and permittivity for miniaturization of VHF-UHF antennas

Spinel ferrites of a nominal composition of Ni0.5Zn0.3Co0.2Fe2O4 (NiZnCo) with various B2O3–Bi2O3–SiO2–ZnO (BBSZ) glass additions were successfully synthesized at a relatively low temperature of 930 °C for their potential applications as magneto-dielectric antenna substrate materials. Measurements of magnetic and dielectric properties show that, with an increasing content of BBSZ from 0 to 2 wt. %, the permeability μ′ at low frequencies was increased from ∼4.7 to ∼8.9, whereas the permittivity ε′ was improved from ∼5.9 to ∼12.5. These tunable permeability and permittivity were proved to be closely related to the grain size and density, based on the magnetic circuit model and effective medium theory. Importantly, the sample with 0.5 wt. % addition demonstrated the optimal magneto-dielectric performance with nearly equivalent values of μ′ and ε′, which yields a large miniaturization factor of ∼6.5 and the normalized impedance of ∼1 over the frequency range of 10 MHz–1 GHz. Moreover, this sample exhibits low loss characteristics over a wide frequency range, where the dielectric loss tan δε is in the order of 10−3 and the magnetic loss tan δμ is less than 0.15. These properties make the ferrite material a promising candidate for miniaturized antennas with good impedance matched to free space and open a great potential for low-temperature co-fired ceramic applications toward the practical fabrication and high integration of the antennas.

Evidence of Magnetoelectric coupling in Bi2(1-x)Ho2xFe4O9 (x=0, 0.01) multiferroic ceramics

We report structural, magnetic, dielectric and magnetoelectric properties of orthorhombic Bi2(1-x)Ho2xFe4O9 (x=0, 0.01) ceramics (space group ‘Pbam’) synthesized by conventional solid state reaction route. Rietveld refined X-ray diffraction (XRD) shows phase formation of the samples along with reduction in lattice parameters and cell volume due to lower ionic radii substitution of Ho3+ at Bi3+-site. DC magnetization study revealed antiferromagnetic transition (TN) of the parent (BFO = 250 K) as well as 1% Ho substituted sample (BHFO1 = 253 K) along with increase in magnetization. Opening of hysteresis was observed for BHFO1 sample implying onset of weak ferromagnetism with dominating antiferromagnetic behaviour. Moreover, temperature dependent dielectric (ε') study and its derivative (dε'/dT) for both the samples show significant anomaly around the antiferromagnetic transition (TN) thus, implying a plausible magnetoelectric coupling between the magnetic as well as the electric order parameters in the studied samples. Magnetoelectric coupling was also confirmed from temperature and magnetic field (1.3 T) dependant tan loss plots.