Compositional,temperature and frequency dependence of dielectric behaviour of zinc substituted copper- ferri-chromates

The comprehensive study on compositional, temperature and frequency dependent dielectric properties of Zn_xCu_1−xFeCrO₄ (x = 0.0, 0.2, 0.4 and 0.6 ) was carried out by means of a. c. resistivity (ρ_ac), dielectric constant (ε′) and loss tangent (tanδ) measurements in the frequency range from 100 Hz to 1 MHz at different temperatures ranging from 40 °C to 500 °C. An abnormal behaviour of ε′ as a function of temperature is explained on the basis of contribution of two types of charge carriers in the polarization process. It is found that magnetic ordering does not have marked influence on the dielectric properties. The probable conduction mechanism in the present system is due to electron transition such as Fe²⁺ Fe³⁺ and Cu²⁺ Cu¹⁺ rather than ionization or polaron hopping mechanism.     

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.     

Structural,Electrical and Dielectric Properties of Co–Mn Spinel Nanoferrites Prepared by Co-precipitation Technique

Cobalt manganese nanoceramics with nominal composition Co_1−x Mn _x Fe₂O₄ (x=0.00, 0.15, 0.30, 0.45, 0.60, 0.75) were synthesized by a chemical coprecipitation technique. The X-ray diffraction patterns revealed the cubic spinel structure. The average crystallite size from the Sherrer formula was in the range of 28 nm–56 nm. The lattice parameter increased with a concentration of manganese. Scanning electron microscopy (SEM) was used for microstructural study. The electrical properties such as electrical resistivity (ρ), drift mobility (μ _d), and activation energy (ΔE) were measured using a two-probe apparatus in the temperature range 323–573 K. The electrical resistivity decreased with temperature and manganese concentration. The dielectric constant (ε′), loss factor or imaginary loss (ε″) and dielectric tangent loss (tan δ) were measured at room temperature using a LCR meter in the frequency range 100 Hz to 5 MHz. All the dielectric parameters decreased with increasing frequency. The AC electrical conductivity (σ _ac) was calculated from the dielectric measurements. It increases with increase of frequency and manganese concentration. The increase in electrical conductivity may be attributed to the formation of Co⁺³ and Mn⁺³ from Co⁺² and Mn⁺³, respectively, at both A and B sites.     

Effect of bismuth on the properties of Mn ferrite nanoparticles prepared by co-precipitation method

Nanoparticles of MnBi_xFe_2−xO₄(x = 0.0, 0.02, 0.04, 0.06) have been synthesized by a chemical co-precipitation method. X-ray diffraction analysis (XRD) reveals that bismuth exits in its Bi³⁺ and Bi⁵⁺ state. It was also observed that bismuth substitution enhances the grain growth and density. The dielectric constant (ε′) and the loss tangent (tan δ) increases with increase in bismuth content. Resistivity (ρ) and maximum magnetization (M) was found to decrease with increasing bismuth content.     

Studies on electrical properties of ( x ) BaTiO3?+?(1? x ) Ni0.92Co0.03Mn0.05Fe2O4 ME composites

The (1−x) Ni_0.92Co_0.03Mn_0.05Fe₂O₄ + (x) BaTiO₃ magnetoelectric (ME) composite have been prepared using conventional double sintering ceramic process where x varies as 1.00, 0.85, 0.70, 0.55 and 0.00. The presence of both phases has been confirmed by X-ray diffraction and the microstructure study will be carried out by SEM technique. The dc resistivity and thermo-emf of the samples have been studied with variation in temperature. The variation of dielectric constant (έ) and loss tangent (tan δ) will be measured in the frequency range 100 Hz–1 MHz. The ac conductivity has been derived from dielectric constant (έ) and loss tangent (tan δ). The static value of magnetoelectric conversion factor dc (ME)_H has been studied as a function of intensity of magnetic field.     

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.     

Synthesis and dielectric properties of MXTi<Subscript>7</Subscript>O<Subscript>16</Subscript> (M = Ba and Sr; X = Mg and Zn) hollandite ceramics

MXTi₇O₁₆ (M = Ba and Sr; X = Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric properties such as dielectric constant (ε_r), loss tangent (tan δ) and temperature variation of dielectric constant (τ_εr) of the sintered ceramic compacts are studied using an impedance analyser up to 13 MHz region. The strontium compounds have relatively high dielectric constant and low loss tangent compared to the barium analogue. The phase purity of these materials has been examined using X-ray diffraction studies and microstructure using SEM method.     

High-frequency dielectric behaviour of Li–Mg ferrites

Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tanδ) of mixed Li–Mg ferrites have been measured at room temperature in the frequency range 1 to 13 MHz using an 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 (tanδ) is found to be abnormal, giving a peak at certain frequency for all mixed Li–Mg ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent.     

Dielectric behaviour of MgFe2O4 prepared from chemically beneficiated iron ore rejects

Chemically beneficiated high silica/alumina iron ore rejects (27–76% Fe₂O₃) were used to synthesize iron oxides of purity 96–98% with SiO₂/Al₂O₃ ratio reduced to 0.03. The major impurities on chemical beneficiations were Al, Si, and Mn in the range 2–3%. A 99.73% purity Fe₂O₃ was also prepared by solvent extraction method using methyl isobutyl ketone (MIBK) from the acid extracts of the ore rejects. The magnesium ferrite, MgFe₂O₄, prepared from these synthetic iron oxides showed high resistivity of ∼ 10⁸ ohm cm. All ferrites showed saturation magnetization, 4πM_s, in the narrow range of 900–1200 Gauss and the Curie temperature,T, _cof all these fell within a small limit of 670 ± 30 K. All ferrites had low dielectric constants (ε′), 12–15, and low dielectric loss, tan δ, which decreased with the increase in frequency indicating a normal dielectric dispersion found in ferrites. The presence of insignificant amount of polarizable Fe²⁺ ions can be attributed to their high resistances and low dielectric constants. Impurities inherent in the samples had no marked influence on the electrical properties of the ferrites prepared from the iron ore rejects, suggesting the possibility of formation of ferrite of constant composition, MgFe₂O₄, of low magnetic and dielectric losses at lower temperatures of 1000°C by ceramic technique.     

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.     

Dielectric relaxation in Se<Subscript>80−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>20</Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> chalcogenide glasses

This study reports the temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε′′) in glassy Se_80−x Te₂₀Sn _x (x = 0, 2, 4, 6) alloys. The measurements have been made in the frequency range (1–500 KHz) and in the temperature range 305–335 K. The results indicate that the dielectric dispersion exists in the present glassy systems in the above frequency and temperature range. The composition dependence of the dielectric constant, dielectric loss and activation energy thermally activated crystallization is also discussed.     

Dielectric properties of a ceramic oxide: Li(Ni<Subscript>7/10</Subscript>Fe<Subscript>3/10</Subscript>)VO<Subscript>4</Subscript>

The Li(Ni_7/10Fe_3/10)VO₄ compound has been synthesized by solution-based chemical route. Its dielectric response is investigated using complex impedance spectroscopy technique. Frequency dependence of dielectric constant (ε_r) at different temperatures shows low-frequency dispersion due to polarized structure of the material and mobile charge carriers. Temperature dependence of ε_r at different frequencies exhibits the dielectric anomalies in ε_r at different temperatures. Dielectric relaxation process in the material is signified by the variation of tangent loss with frequency at different temperatures. The variation of relaxation time with temperature obeys the Vogel–Fulcher law.     

Dielectric properties of NaF-B2O3 glasses doped with certain transition metal ions

Dielectric constant ε, loss tan δ, a.c. conductivity Σ and dielectric breakdown strength of NaF-B₂O₃ glasses doped with certain transition metal ions (viz. Cu²⁺, VO²⁺, Ti⁴⁺ and Mn⁴⁺) are studied in the frequency range 10²-10⁷ Hz and in the temperature range 30–250°C. The values of ε, tan δ, Σ_a.c. are found to be the highest for Cu²⁺ doped glasses and the lowest for Mn⁴⁺ doped glasses. Activation energy for a.c. conduction and the value of dielectric breakdown strength are found to be the lowest for Cu²⁺ doped glasses and the highest for Mn⁴⁺ doped glasses. With the help of infrared spectra, increase in the values of ε and tan δ of these glasses with frequency and temperature are identified with space charge polarization. An attempt has been made to explain a.c. conduction phenomenon on the basis of quantum mechanical tunneling model (QMT)/carrier barrier hopping model.     

Magnetoelectric and dielectric properties of Ni0.5Cu0.5Fe2O4–Ba0.5Pb0.5Ti0.5Zr0.5O3 ME composites

The (x) Ni_0.5Cu_0.5Fe₂O₄ + (1−x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ ME composites have been synthesized by a standard ceramic method. The presence of single phase in x = 0 and x = 1 as well as two phases in x = 0.15, 0.30 and 0.45 composites has been confirmed by XRD. The dielectric constant (ε′) and dielectric loss (tan δ) have been studied as a function of temperature and frequency. These composite materials exhibit maximum dielectric constant with a variation of frequency and temperature. The composite 15% Ni_0.5Cu_0.5Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ had the highest magnetoelectric voltage coefficient of 0.248 mV/cm Oe at room temperature among the studied composites.     

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.     

High-frequency dielectric behaviour of polycrystalline zinc substituted cobalt ferrites

The dielectric constant () and complex dielectric constant () of zinc substituted cobalt ferrites have been measured at room temperature in the high frequency range 100 kHz to 1 MHz. The values of dielectric loss tangent (tan ) have been computed from and . Plots of dielectric constant () versus frequency show a normal dielectric behaviour of the spinel ferrites. The frequency dependence of dielectric loss tangent (tan ) is found to be abnormal, giving a peak at certain frequency for all the ferrites under investigation. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. The dielectric constant for these mixed ferrites is approximately inversely proportional to the square root of the resistivity. A plot of dielectric constant versus temperature shows a transition near the Curie temperature. An attempt is made to explain the possible mechanism for this observation.     

Dielectric characteristic and local phase transition of gallium phosphide nanosolid

The dependences of relative dielectric permittivity, ε′ _r, and tangent of dielectric loss angle, tg δ, of gallium phosphide (GaP) nanosolid on frequency and temperature were investigated. The GaP nanopowders are subglobular in shape, with the average crystallite size of about 50 nm evaluated from Scherrer equation. It can be concluded that the leakage current mechanism plays an important role in the dielectric loss of the GaP nanosolid. The dielectric characteristic of the GaP nanosolid in the range 298–350 K allows to detect an ε′ _r or tg δ peak at 303 K that is due to local phase transitions, probably in the high hydrostatic stress field of dislocations with an edge component. Under the influence of an electric field, the high hydrostatic stress field of dislocations can undergo changes in deformation, accompanied by drastic stress-induced changes in the order parameter near the phase transition temperature, and hence, changes in the Gibbs free energy per unit volume can be found.     

Magnetic and Dielectric Properties of <Emphasis Type="Italic">R</Emphasis><Subscript>2</Subscript>CuTiO<Subscript>6</Subscript> Compounds (<Emphasis Type="Italic">R</Emphasis>=Y,La, Pr and Nd)

Magnetic and dielectric properties of the double perovskite compounds of the type R ₂CuTiO₆ (RCTO, where R=Y, La, Pr and Nd) has been studied. Y₂CuTiO₆ (YCTO) crystallizes in a hexagonal unit cell, whereas the other three compounds form into orthorhombic structure. All four compounds show paramagnetic behavior down to 5 K. The dielectric studies show moderate dielectric constant (ε′) and very small dielectric loss (tan δ) for YCTO. The orthorhombic members of RCTO compounds exhibit moderate values of ε′ and tan δ. The dielectric properties are presented and discussed here in the light of the influence of structure and rare-earth ions on the physical properties of RCTO compounds.     

Characterization and dielectric properties of almandine-pyrope garnet

Some garnets collected from the Kothagudem area of Khammam district in Andhra Pradesh were characterized by chemical analysis. The results show the garnets to be of almandine (Fe⁺² ₃ Al₂Si₃O₁₂) pyrope (Mg₃Al₂Si₃O₁₂) group. Dielectric constant (ɛ) and dielectric loss (tanδ) were measured as a function of frequency and temperature in the frequency range of 100 Hz to 100 KHz and from room temperature to 400°C. The room temperature measurement was extended to 10 MHz, AC conductivity was calculated from the data on ε and tan δ. DC conductivity was also measured.     

Dispersion of dielectric constant and resistivity of Cu x Zn1−x Fe2O4 samples

Cu _x Zn_1−x Fe₂O₄ samples exhibit dispersion of dielectric constant, tanδ and resistivity in the frequency range of 1 kHz to 50 MHz. The dispersion exhibited is in general accord with Koops’ model. However, the details of the conducting and non-conducting regions must be taken into account when composition tends to change interrelationship between the elementary capacitor resistor circuits. On quenching these samples from 800°C the dielectric constantε ¹ showed an increase for CuFe₂O₄ and Cu_0·8Zn_0·2Fe₂O₄ samples. The dielectric constant of the remaining samples showed no influence on quenching. The compositional variation showed that the dielectric constant has higher value for the ferrite Cu_0·4Zn_0·6Fe₂O₄ The results are explained on the basis of cation transfer.