Dielectric behaviour of erbium substituted Mn-Zn ferrites

Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tan□δ) of mixed Mn-Zn-Er ferrites having the compositional formula Mn_0.58Zn_0.37Fe_2.05−xEr_x0₄ (where itx = 0.2, 0.4, 0.6, 0.8 and 1.0) were measured at room temperature in the frequency range 1–13 MHz using a HP 4192A impedance analyser. Plots of dielectric constant (ε′) vs frequency show a normal dielectric behaviour of spinel ferrites. The frequency dependence of dielectric loss tangent (tan δ) was found to be abnormal, giving a peak at certain frequency for all mixed Mn-Zn-Er ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. Plots of dielectric constant vs temperature have shown a transition near the Curie temperature for all the samples of Mn-Zn-Er ferrites. However, Mn_0.58Zn_0.37Er_1.0Fe_1.05O₄ does not show a transition. On the basis of these results an explanation for the dielectric mechanism in Mn-Zn-Er ferrites is suggested.     

AC-field Frequency Response of?Cu0.5Tl0.5Ba2(Ca2?qMgq)Cu3O10?δ Bulk Superconductor

The dielectric properties of Cu_0.5Tl_0.5Ba₂Ca_2−q Mg _q Cu₃O_10−δ (q=0, 0.5, 1.0 1.5) superconductor samples were studied at two temperatures of 80 and 290 K by capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz. We have presented the measurements of the dielectric constants (ε′ and ε″), dielectric loss factor (tan δ) and ac-conductivity (σ _ac) as a function of frequency and temperature. A negative capacitance (NC) experience has been observed, which is most likely due to different contact electrodes and superconductor samples’ Fermi levels. Since metals have their Fermi levels higher than ceramics, there is a flow of the carriers from the ceramic samples towards the metal electrodes. The dielectric polarization phenomenon is observed, which is due to dislodgment of mobile charges from their equilibrium position relative to fixed charges of the reservoir layer. The improved inter plane coupling promoted by Mg substitution at Ca site would change the dielectric response of Cu_0.5Tl_0.5Ba₂Ca_2−q Mg _q Cu₃O_10−δ superconductors. To observe such effects in Mg doped Cu_0.5Tl_0.5Ba₂Ca_2−q Mg _q Cu₃O_10−δ superconductors, di- electric measurements were carried out both at room temperature (290 K) and in the superconducting state closer to the boiling point of liquid nitrogen (80 K). The excess conductivity arising due to superconducting state of material has been determined, and its role in the mechanism of superconductivity is suggested. The negative dielectric constant (ε′) and dielectric loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 80 K may enhance the polarizability and hence the dielectric constants (ε′ and ε″).     

Dielectric properties of Al-substituted Co ferrite nanoparticles

A series of polycrystalline spinel ferrites with composition, CoFe_2−x Al _x O₄ (0 ≤ x ≤ 1), have been synthesized by sol-gel method. The effect of Al-substitution on structural and dielectric properties is reported in this paper. X-ray diffraction analysis revealed the nanocrystalline nature in the prepared ferrite samples. The particle size, D, decreases with increase in Al-content. The lattice parameter, a and X-ray density, d _x , decreased with increase in Al-content. The dielectric properties for all the samples have been studied as a function of frequency in the range 100 Hz–10 MHz. Dielectric properties such as dielectric constant, ɛ′, dielectric loss, ɛ″ and dielectric loss tangent, tan δ, have been studied for nanocrystalline ferrite samples as a function of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrites proposed by this technique possess lower value than that of the ferrites prepared by other methods for the same composition. The low dielectric behaviour makes ferrite materials useful in high frequency applications.     

Study of the dielectric parameters of aluminium ore bauxite of Mainpat area of Chhattisgarh at X-band frequency

A simple method for measuring the dielectric parameter of materials in the form of powders at microwave frequencies is suggested. Measurement of the permittivity ε′ and ge″ at 9·967 GHz on powder samples of the aluminum ore bauxite gives interesting results. It is found that ε′ and ε″ increases with packing densities (δ ). Further ε′ and ε″ also depend upon the percentage of Al₂O₃. These results show that the values of ε′ and ε″ can be used to set certain basic values for minability of the ore for a particular sample. Conductivities (σ) and relaxation (τ) are also calculated in the present studies     

Studies of the temperature coefficient of capacitance (TCC) of a new electroceramic composite: Pb(Fe0.5Nb0.5)O3 (PFN)–Cr0.75Fe1.25O3(CRFO)

In this paper we did a study of the dielectric properties: capacitance (C), dielectric permittivity(ε), electric modulus(M) and dielectric loss(tangα)) in the radio-frequency(RF) and microwave (MW) frequency range as a function of temperature and the temperature coefficient of capacitance (TCC) of the composites [Pb(Fe_1/2Nb_1/2)O₃(PFN)]_Z–[Cr_YFe_2−YO₃(CRFO)]_100−Z where Z = 0, 10, 50, 90 and 100%. The compounds were prepared by the powder-sintering and the X-ray diffraction (XRD) was used in this study using the Rietveld procedure. The X-ray analysis shows that PFN phase is tetragonal where the CRFO phase belongs to a trigonal structure. The capacitance, dielectric permittivity, electric modulus and loss were studied in the frequency range of 100 Hz to 1GHz and temperature range of 25–100 °C. The values of TCC for all the samples are presenting positive values. The study of the electric modulus (M) as a function of frequency and temperature lead to the measurement of the activation energy (E_ac), which is directed linked to the relaxation process associated to the interfacial polarization effect in the samples. The study of the electrical properties in the RF and MW range of frequencies is important in view of possible applications of these composites as future components in RF and MW circuits.     

Frequency-dependent dielectric and electric modulus properties of Li–Ni–Sm–Fe–O spinel embedded in conducting polymer

Conducting polymeric nanocomposite containing Li–Ni–Sm–Fe–O spinel was synthesized by the chemical oxidizing of aniline in the presence of LiNi_0.5Sm_0.08Fe_1.92O₄ particles. The dielectric and electric modulus properties of the as-prepared samples were investigated over a frequency range from 10⁶ to 10⁹ Hz. The dielectric constant (ε′), dielectric loss (ε″) and dissipation factor (tan δ) for all samples presented relatively high values at low frequency and were found to decrease with the frequency. The values of ε′, ε″ and tan δ of the nanocomposite were lower than that of the pristine PANI. Electric modulus analysis had been carried out to understand the electrical relaxation process. The dielectric relaxation time for the nanocomposite became longer due to the introduction of LiNi_0.5Sm_0.08Fe_1.92O₄ particles lowering the crystallinity of PANI.     

Electrical conductivity and dielectric properties of cadmium thiogallate CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript> thin films

Cadmium thiogallate CdGa₂S₄ thin films were prepared using a conventional thermal evaporation technique. The dark electrical resistivity calculations were carried out at different elevated temperatures in the range 303–423 K and in thickness range 235–457 nm. The ac conductivity and dielectric properties of CdGa₂S₄ film with thickness 457 nm has been studied as a function of temperature in the range from 303 to 383 K and in frequency range from 174 Hz to 1.4 MHz. The experimental results indicate that σ_ac(ω) is proportional to ω ^s and s ranges from 0.674 to 0.804. It was found that s increases by increasing temperature. The results obtained are discussed in terms of the non overlapping small polaron tunneling model. The dielectric constant (ε′) and dielectric loss (ε″) were found to be decreased by increasing frequency and increased by increasing temperature. The maximum barrier height (W _m) was estimated from the analysis of the dielectric loss (ε″) according to Giuntini’s equation. Its value for the as-deposited films was found to be 0.294 eV.     

Measurement of dielectric properties of high-absorption materials at microwave frequencies

A method is proposed for measuring the dielectric constant ε′ and dielectric loss ε″ of high-absorption dielectric materials by measuring the reflection of electromagnetic radiation with the aid of an adjustable quarter-wave matching plate of nonabsorbing material close to the dielectric surface. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 45–47, May, 1999.     

Electric and dielectric properties of solution-gas interface-grown PbS films

Dielectric properties andI–V characteristics of solution-gas interface-formed PbS thin-film capacitors (Al/PbS/Al) of various thicknesses have been studied in the frequency range 10-10⁶ Hz at various temperatures (300–443 K). Current-voltage (I–V) characteristics show space-charge-limited conduction. Dielectric constant (ε) increases with increasing film thickness and temperature and decreases with increase of frequency. The loss factor (tanδ) peaks observed in tanδ vs frequency and tanδ vs temperature reveal relaxation effect from dipolar orientation. These maxima shift to higher-temperature region with increasing frequency. The large increase in capacitance (C) and dielectric constant (ε) towards low-frequency (f) region indicates the possibility of an interfacial polarization mechanism in this region.     

Dielectric properties of carbon black: SBR composites

A series of styrene–butadiene rubber (SBR) composites have been prepared with different weight ratios of polyacetylene based conducting carbon black (CCB) (0–90 phr). The SBR–CCB systems are characterized for dimensional stability which is enhanced by increasing the CCB loading because of enhancement in polymer-filler interaction. The electrical properties such as dielectric constant (ε_r), dissipation factor (tan δ) and dielectric loss (ε″) of the composites have been studied. The influence of different loading of CCB (0–90 phr), frequency of ac (100 Hz–30 MHz) and temperature (25–75 °C) on the electrical properties was studied. An increase in dielectric constant and tan δ of the SBR composites was observed with increase in CCB content and ac frequency. This is due to enhancement of filler–filler interaction and the increase in continuity of conducting phase. The surface morphology has been studied using scanning electron microscopy (SEM).     

Dielectric and impedance spectroscopy studies on sisal fibre-reinforced polyester composite

Frequency and temperature dependence of dielectric constant (ε_r), dielectric loss (tanδ), ac conductivity (σ_ac) and complex impedance spectroscopy studies on cured polyester matrix and sisal fibre-reinforced polyester composites (SFRPC) have been investigated in the frequency range from 180 Hz to 1 MHz and temperature range from room temperature to 200 °C. The experimental results showed that with the incorporation of sisal fibre, the values of ε_r, tanδ and σ_ac are increased. It is also found that the values of ε_r and tanδ for both cured polyester matrix and SFRPC are decreased with increasing frequency, which indicates that the major contribution to the polarization may come from orientation polarization and interfacial polarization. The increasing value of ε_r with increasing temperature at a particular frequency is due to free motion of the dipole molecular chains within the cured polyester matrix and SFRPC at higher temperature.     

Impact of metal filler on the dielectric properties of Nylon 11

Dielectric measurements of pure Nylon 11 in comparison with metal (Zn) filled Nylon 11 have been carried out using an impendence analyzer in the frequency range of 10²–10⁷ Hz and temperature range 20–120 °C. Two different concentrations (1% and 5% (w/w)) of metal (Zn) fillers were used. It was observed that at low frequencies and particularly at high temperature dielectric permittivity (ε′) for 1% Zn filled sample is more than that of pure Nylon 11 whereas ε′ for 5% Zn filler is less as compared to that for pure Nylon 11. But at very high frequencies dielectric permittivity (ε′) for pure Nylon 11 is less than Zn filled samples. Also it is found that for all frequencies and particularly at high temperature ε′′ as well as tan δ are maximum for pure Nylon 11 and decrease for filled Nylon 11 samples. The Cole–Cole arcs have also been plotted for these samples. Using these plots the static and instantaneous values of dielectric permittivity and orientation polarization parameter ‘S’ have been calculated.     

Conductive carbon black-filled ethylene acrylic elastomer vulcanizates: physico-mechanical,thermal, and electrical properties

The effect of conductive carbon black (CCB) on the physico-mechanical, thermal, and electrical properties have been investigated by various characterization techniques. Physico-mechanical properties of the vulcanizates were studied with variation of filler loading, which revealed that the tensile strength increased up to 20 phr (parts per hundred rubber) CCB loading, whereas at higher filler loading it decreased marginally. Furthermore, tensile modulus, tear strength, and hardness gradually increased with increase in filler loading. The compression set and abrasion loss decreased with increasing CCB loading. The bound rubber content (Bdr) of unvulcanized rubber was found to increase significantly with increasing CCB content. The crosslink density increased, whereas the swelling decreased with CCB loading. The thermal stability of the vulcanizates evaluated by thermogravimetric analysis (TGA) showed a minor increment with increase in CCB content. It is observed from the dynamic mechanical thermal analysis (DMTA) that the storage modulus (E′), loss modulus (E″), and glass transition temperature (T _g) of ethylene acrylic elastomer (AEM) matrix increased by incorporation of CCB. The dielectric relaxation characteristics of AEM vulcanizates such as dielectric permittivity (ε′), electrical conductivity (σ _ac), and electric moduli (M′ and M″) have been studied as a function of frequency (10¹ to 10⁶ Hz) at different filler loading. The variation of ε′ with frequency and filler loading was explained based on the interfacial polarization of the fillers within a heterogeneous system. The ε′ increased with increasing the CCB loading and it decreased with applied frequency. The frequency dependency of σ _ac was investigated using conduction path theory and percolation threshold limit. The σ _ac increased with increase in both CCB concentration and applied frequency. The M′ increased with applied frequency, however, it decreased above 30 phr filler. The M″ peak shifted towards higher frequency region and above 20 phr filler loading the peaks were not observed within the tested frequency region. The electromagnetic interference shielding effectiveness (EMISE) was studied in the X-band frequency region (8–12 GHz), which significantly improved with increase in CCB loading.     

Dielectric response of humid phlogopite

The dielectric response of phlogopite mica has been measured for frequency lying between 10 mHz and 10 kHz with humidity as a parameter. The measured complex capacitance shows a low frequency dispersion (LFD) at high humidities. A weak loss peak is also present at high frequencies and low humidity levels. Work carried out at former Chelsea College, London University, London.     

Effects of coupling agent on the preparation and dielectric properties of novel polymer–ceramic composites for embedded passive applications

The study was carried out to investigate the effects of silane coupling agent, γ-aminopropyl triethoxy silane (KH-550), on the preparation and dielectric properties of Barium titanate (BaTiO₃)/Bisphenol-A dicyanate (2,2′-bis (4-cyanatophenyl) isopropylidene)(BADCy) composites for embedded passive implications. It was found that KH-550 accelerated the polymerization of BADCy and was beneficial to improve the compatibility between BaTiO₃ particles and BADCy matrix. The dielectric constant (ε) and dielectric loss (tanδ) both increased at first and then decreased with the increase of the KH-550 content. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of these composites were not obvious since the dielectric properties of cyanate ester were stable at various frequencies.     

Dielectric properties of Be(IO<Subscript>3</Subscript>)<Subscript>2</Subscript>⋅4H<Subscript>2</Subscript>O crystals

The article studies the dielectric properties, dc conductivity and ac conductivity of Be(IO₃)₂⋅4H₂O single crystals. The dielectric constant ε has been defined for the three directions of the vectors a, b and c in the crystals in the temperature interval 280–340 K and frequency range 100 Hz–10⁶ Hz. The crystals show strongly expressed anisotropy, at 20 ^∘C and frequency 100 Hz ε_a = 235, ε_b = 30 and ε_c = 85. The frequency dependence of ε is evidence of the presence of low-frequency relaxation polarization in the crystals. The activation energies of the three directions in the crystals have been derived from the temperature dependence of dc conductivity, and they are 1.03 eV, 0.836 eV and 1.2 eV respectively.     

Dynamic magneto-electric multiferroics PZT/CFO multilayered nanostructure

Highly oriented PbZr_0.53Ti_0.47O₃/CoFe₂O₄ (PZT/CFO) multilayered nanostructures (MLNs) were grown on MgO substrate by pulsed laser ablation using La_0.5Sr_0.5CoO₃ (LSCO) as conducting bottom electrode. The effect of various PZT/CFO (PC) sandwich configurations having three, five, and nine layers while maintaining total thickness of PZT and CFO be identical has been systematically investigated. X-ray diffraction (XRD) and micro-Raman spectra revealed the existence of pure PZT and CFO phases without any intermediate phase. Intact MLNs were observed by transmission electron microscopy (TEM) with little inter-diffusion near the interfaces at nano-metric scale without any impurity phase. Impedance spectroscopy, modulus spectroscopy, and conductivity spectroscopy were carry out over a wide range of temperatures (100–600 K) and frequencies (100 Hz–1 MHz) to investigate the grain and grain boundary effect on electrical properties of MLNs. Temperature dependent real dielectric permittivity and dielectric loss illustrated step-like behavior and relaxation peaks near the step-up characteristic, respectively. Cole–Cole plots indicate that most of the dielectric response came from the bulk (grain) MLNs below 300 K, whereas the grain boundary and the electrode–MLNs effects are prominent at elevated temperatures. The dielectric loss relaxation peak shifted to higher frequency side with increase in temperature, it was out of the experimental frequency window above 300 K. Our Cole–Cole fitting of dielectric loss spectra indicated marked deviation from the ideal Debye-type of relaxation, which is more at elevated temperature. Master modulus spectra supported the observation from the impedance spectra; it also indicated that the magnitude of the grain boundary compared to grain becomes more prominent with increase in number of layers. We have explained these electrical properties of MLNs by Maxwell–Wagner type contributions arising from the interfacial charge at the interface of the ML structures. Three different types of frequency dependent conduction processes were observed at elevated temperatures (>300 K), which fitted well with the double power law, indicating that the low frequency (<1 kHz) conductivity may be due to long-range ordering (frequency independent), mid frequency conductivity (<10 kHz) may be due to short-range hopping, and high frequency (<1 MHz) conduction due to the localized relaxation hopping mechanism. Ferroelectric polarization decreased slowly in reducing the temperature from 300 to 200 K, with complete collapse of polarization at ~100 K, but there was complete recovery of the polarization during heating, which was repeatable over many different experiments. At the same time, the temperature dependent remanent magnetization of the MLNs showed slow enhancement in the magnitude till 200 K with three-fold increase at 100 K compared to room temperature. This enhancement in remanent magnetization and decrease in remanent ferroelectric polarization on lowering the temperature indicate temperature dependent dynamic switching of ferroelectric polarization. The magnetic and ferroelectric properties of MLNs were quite different compared to individual layers suggesting its improper ferroelectric characteristics. The fatigue test showed almost 0–20% deterioration in polarization. Fatigue and strong temperature and frequency dependent magneto-electric coupling suggest MLNs utility for Dynamic Magneto-Electric Random Access Memory (DMERAM).     

An investigation on electrical properties of microwave treated natural ilmenite (FeTiO3)

It has been observed that microwaves of 2.45 GHz heat dielectric materials. On subjecting natural ilmenite to microwave irradiation, the mineral is observed to heat, with a surface temperature in proportion to the irradiation time. With irradiation times from 40 to 240 seconds (increased in steps of 40 sec), the surface temperature measured on the samples were between 280 and 520 K. Electrical measurements made on the samples before and after irradiation show that the electrical properties are modified by the microwave irradiation. The real conductivity (σ′), dielectric constant (ɛ′) and the dielectric loss (ɛ″) plotted against frequency generally showed universal dielectric behaviour [1 and references therein] similar to that observed in other systems studied in the literature but using conventional heating techniques. Plots of σ′, ɛ′ and ɛ″ against the surface temperature of the sample showed frequency independent peaks around 460 K. The experimental dielectric loss (ɛ″) results fit a peak function of the form:

Compound-LiCo<Subscript>3/5</Subscript>Fe<Subscript>1/5</Subscript>Mn<Subscript>1/5</Subscript>VO<Subscript>4</Subscript> and dielectric characteristics

The LiCo_3/5Fe_1/5Mn_1/5VO₄ compound was successfully synthesized by solution-based chemical method. The variation of dielectric constant (ε_r) with frequency at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of ε_r at different frequencies indicates dielectric anomalies in ε_r at temperature (T_max) = 220, 235, 245, 260 and 275 °C with (ε_r)_max ~ 6,830, 2,312, 1,224, 649 and 305 for 10, 50, 100, 200 and 500 kHz, respectively. The variation of tangent loss with frequency at different temperatures shows the presence of dielectric relaxation in the material. The variation of relaxation time as a function of temperature follows the Vogel-Fulcher relation.     

Dielectric relaxation behaviour of Sr<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>SbMnO<Subscript><Emphasis Type="Bold">6</Emphasis></Subscript> ceramics fabricated from nanocrystalline powders prepared by molten salt synthesis

Double perovskite polycrystalline single phase and dense Sr ₂ SbMnO ₆ (SSM) ceramics, fabricated using the nanocrystalline powders synthesized by molten salt method, exhibited high dielectric constant with low dielectric loss as compared to that of SSM ceramics obtained from the powders prepared by solid-state synthesis method. The dielectric data obtained over a wide frequency (100 Hz–1 MHz) and temperature (190 K–300 K) ranges exhibited distinct relaxations owing to both the grain and grain boundary. The dielectric dispersion was modeled using the Cole–Cole equation consisting of two separate relaxation terms corresponding to the grain and grain boundary. The grain and grain boundary relaxations observed in the Nyquist plots (Z ^′ and Z ^″) were modeled by an equivalent circuit consisting of two parallel RC circuits connected in series with each other. A careful analysis of both the impedance (Z ^″ vs ω) and modulus (M ^″ vs ω) behaviour corroborated the conclusions drawn from the dielectric data.