Structural,dielectric and ac conductivity properties of Ni-doped HoFeO3 before and after gamma irradiation

A series of samples of HoFe_1?x Ni _x O₃ (x = 0.0, 0.1, 0.3) were prepared using the solid-state reaction technique to understand the structural, dielectric and conductivity properties before and after gamma irradiation of accumulated dose of 625 KGy. The X-ray diffraction confirms that all the samples exist in single-phase orthorhombic structure having space group Pbnm. With increasing dopant Ni, the unit cell volume and lattice parameters undergo small change. X-ray analysis show change in the interplanar spacing and full width at half maximum values after gamma irradiation. The Raman spectra of the samples show modifications after gamma irradiation. It can be easily seen that after gamma irradiation intensity, peak width are completely altered by gamma-absorbed dose. Measurement of dielectric loss and dielectric constant at room temperature was performed before and after gamma irradiation in the frequency range of 20 Hz–1 MHz. It is observed that the value of dielectric constant decreases after irradiation. The ac conductivity is estimated from the dielectric constant and loss tangent. Exposure to gamma radiation results in substantial modification in the physical properties of the Ni-doped Ho-based orthoferrites.     

Dielectric response of KCN crystal at ultra low frequencies

The dielectric response of pure KCN crystals (ε′, ε″ and tg σ) has been measured as a function of temperature in the frequency range 10⁻² Hz to 10⁴ Hz. In the antiferroelectric phase the width of the loss peak are found practically independent of temperature (1.4 decades) and close to a Debye behavior; the relaxation time of the CN⁻ dipoles is characterized by an Arrhenius behavior τ = τ₀ exp (U/KT) with τ₀ = 7.26 × 10⁻¹⁵s and U = 0, 147 eV confirming a classical temperature activated reorientation of the dipoles.     

Effect of gamma irradiation on the dielectric properties and electrical conductivity of the TlInS<Subscript>2</Subscript> single crystal

The effect of gamma irradiation on the dielectric properties and ac conductivity of a TlInS₂ single crystal with a layered structure has been investigated in the frequency range from 5 × 10⁴ to 3.5 × 10⁷Hz. It has been shown that gamma irradiation of the TlInS₂ single crystal with a dose of 10⁴–2.25 × 10⁶ rad leads to a considerable increase in the dielectric loss tangent tanδ, the real part ɛ′ and imaginary part ɛ″ of the complex permittivity, and the ac conductivity σ _ac across the layers. It has been established that, for all gamma irradiation doses, the TlInS₂ single crystal is characterized by the dielectric loss due to electrical conduction up to a frequency of 10⁷ Hz and by the relaxation loss at a higher frequency. Irradiation of the TlInS₂ single crystal results in an increase in the dispersion of tan δ, ɛ′, and ɛ″. It has been demonstrated that, as the gamma irradiation dose is accumulated in the TlInS₂ single crystal, the density of localized states near the Fermi level N _F increases (from 5.2 × 10¹⁸ to 1.9 × 10¹⁹ eV⁻¹ cm⁻³).     

Ac electrical conductivity and dielectric relaxation behavior of amorphous Selinum36 Antimony31Cubber33 thin films

ABSTRACT

The alternating-current (Ac) conductivity measurements and dielectric behaviors were observed in the range of temperature (from 303 to 393?K) and in the frequency range from 10² to10⁶?Hz for amorphous films of Selinum₃₆ Antimony₃₁ Cubber₃₃ chalcogenide glass. The ac conductivity has temperature dependency and the frequency dependency. The reduction of the exponent S values with raising temperature was introduced with the correlated barrier hopping model. The maximum height of the barrier W_M for Sellinum₃₆ Antimony₃₁Cubber₃₃ films is reliable with carrier hopping over a potential barrier. The number of localized states per unit volume at the Fermi level enhances with the elevation of ambient temperature of the film sample. Both dielectric constant ε₁ and loss ε₂ increase with the rise of temperature rising and decrease with frequency. The computation of the dielectric modulus M^/ and M^// revealed that the interfacial is the most suitable polarization type.     

Microwave electrophysical properties of superionic crystals Ag2HgI4

The paper concerns itself with the investigation results of temperature dependencies of electric conduction and dielectric properties of Ag₂Hgl₄ crystals in the frequency range of 10⁷–7,8·10¹⁰ Hz. The obtained data have shown that in α-phase at T=326 K, the electric conductivity σ is proportional v^0,28 in the frequency range of 10⁷–10⁹ Hz and σ is proporti onal v^0,5 in the range of (1,1–78)·10⁹ Hz. The dependence σ(v) in the range of (1,1–78)·10⁹ Hz may be conditioned by the jumping mechanism of the conductivity and low frequency oscillations of the crystal lattice. It is believed, tha in the σ-phase of Ag₂Hgl₄ a condition of the existence of the ionic polaron is satisfied. The activation energy of the polaron is ΔE_p=0,09 eV.     

低温氮化硅薄膜的介电性能研究

研究了微波电子回旋共振等离子体化学汽相沉积低温氮化硅薄膜在5—10⁶Hz频率范围内的介电性能．由于低温氮化硅薄膜为具有分形结构的纳米非晶薄膜，致使氮化硅薄膜的介电谱、损耗谱在低频区和高频区具有两种不同的分布规律．在低频区介电谱具有ε′∝ω^n－1₁的关系，ｎ₁在0.82—0.88之间，是电子跳跃导电的结果；在高频区介电谱具有ε′∝ω^n-1₂的关系，n₂在0 关键词：     

Impact of MoO3 concentration,frequency and temperature on the dielectric properties of zinc phosphate glasses

Phosphate glasses with the chemical composition of 47P₂O₅–24ZnO-(29-x)Na₂O-xMoO₃, x = 0, 2, 4, 6, 8 and 10, have been prepared using the melt quenching technique. Dielectric properties of these phosphate glasses are carried out in the frequency range from 1 to 100 kHz at different temperatures. Dielectric parameters such as dielectric constant ε′, dielectric loss ε′′ and ac conductivity of the investigated glasses have been evaluated. The dependences of these dielectric parameters on frequency, composition and temperature have been discussed. It is found that dielectric constant decreases with increasing frequency due to the reduction of space-charge polarization and dipole polarization. The dependence of ac conductivity on the MoO₃ content indicates a competition between electronic and ionic conduction. The temperature dependence of the dielectric parameters reveals a rising trend of the dielectric parameters with temperature. This rising trend is indicated due to the increase of the amplitude of the thermal vibration of the charge carriers which facilitates the electron hopping and drifting of the mobile ions. The linear trend of the ln(σ_ac)-1000/T plot indicates that ac conductivity of the investigated glasses is thermally-activated transport process and follows the Arrhenius equation. The activation energy and its composition dependence have been reported.     

Dielectric losses in the triglycine sulfate crystal under heating and cooling

Temperature dynamics of the dielectric spectra and domain structure in the triglycine sulfate (TGS) hydrogen-containing ferroelectric under heating and cooling has been studied using the dielectric spectroscopy and atomic-force microscopy methods. The dielectric spectra are analyzed by the temperature-frequency dependences of the losses ε″ and by the temperature behavior of the maximum losses ε″_max in the dispersion region at frequencies ranging from 102 to 106 Hz. A dynamic conductivity model is proposed for calculating temperature dependences of losses ε″_max. The domain structure dynamics during the heating and cooling of the TGS crystal near the phase transition is studied using the in situ piezoresponse force microscopy. It is experimentally and theoretically shown that the relaxation dispersion is governed by the binding of strongly correlated dipoles with the main lattice that serves as a thermostat.     

纳米Si/C/N复相粉体的微波介电特性

研究了纳米Si/C/N复相粉体在8.2—18GHz的微波介电特性,采用双反应室激光气相合成纳米粉体装置,以六甲基二硅胺烷((Me₃Si)₂NH)(Me∶CH₃)为原料,用激光诱导气相反应法合成纳米Si/C/N复相粉体,复相粉体的粒径为20—30nm.纳米Si/C/N复相粉体与石蜡复合体的介电常量的实部(ε′)和虚部(ε″)以及介电损耗角正切(tan δ=ε″/ε′)随纳米粉体含量的增加而增大,ε′和ε″与纳米粉体体积分数(v)之间符合二次函 关键词： 纳米Si/C/N复相粉体 微波介电常量 微观结构     

Phase transition and electrical investigation in lithium copper pyrophosphate compound Li<Subscript>2</Subscript>CuP<Subscript>2</Subscript>O<Subscript>7</Subscript> using impedance spectroscopy

Lithium pyrophosphate compound Li₂CuP₂O₇ has been synthesized through solid state reaction method. FTIR and XRD results, realized at room temperature, indicate respectively the dominant feature of pyrophosphate anion (P₂O₇)^4? and a pure monoclinic phase with I2/a space group. Electrical and dielectric properties have been studied using impedance spectroscopy complex over a wide temperature (576–710 K) and frequency (209 Hz–1 MHz) range. From the direct and alternative conductivities (DC and AC), electrical conduction is found to be thermally activated process. The frequency-dependent AC conductivity obeys Jonscher’s universal power law σ_AC~Aω^s. The differential scanning calorimetry spectrum discloses phase transition at 622 K.     

Influence of Nd:YAG laser irradiation on AC impedance and dielectric properties of lithium ferrite

Polycrystalline samples of Li_0.5Fe_2.5O₄ spinel ferrite have been synthesized by a standard ceramic technique. The samples were irradiated with an Nd:YAG laser to study the effect of laser irradiation on the structural, dielectric and AC impedance properties. The X-ray diffraction results show the formation of a disordered cubic structure after irradiation. The dielectric constant (?′), dielectric loss (?″) and the loss tangent (tan δ ) were measured at room temperature as a function of frequency (f=20 Hz–1 MHz) for the irradiated and unirradiated samples of Li_0.5Fe_2.5O₄ spinel ferrite. The dielectric constant of the irradiated samples is decreased in magnitude compared to the unirradiated samples. It was found that laser irradiation increases the polarization and the resistivity of the samples as a result of electronic rearrangement and lattice defects. The AC conductivity of the samples was derived from the dielectric constant and loss tangent data. The change in AC conductivity is attributed to the creation of lattice vacancies after laser irradiation. The AC impedance analysis was used to separate the grain and grain boundary of the Li_0.5Fe_2.5O₄ spinel ferrite.     

Modification of the dielectric properties of copper-doped CdIn2S4 single crystal

The study of the dielectric properties of a CdIn₂S₄〈3 mol % Cu〉 single crystal in alternating-current (ac) electric fields with frequencies f = 5 × 10⁴?3.5 × 10⁷ Hz has revealed the origin of dielectric loss (relaxation loss that is changed by the through current loss at high frequencies). It has been found that CdIn₂S₄〈Cu〉 has permittivity increment Δ?′ = 123, relaxation frequency f _r = 2.3 × 10⁴ Hz, and relaxation time τ = 43 μs. The doping of CdIn₂S₄ single crystal with copper (3 mol %) is established to substantially increase the permittivity (?′), dielectric loss tangent (tanδ), and ac conductivity (σ_ac). In this case, the frequency dispersion of ?′ and tanδ increases and that of σ_ac decreases.     

Synthesis and electrical properties of Y2O3: Dy3+ & Eu3+ nanoparticles

Yttrium oxide (Y₂O₃) doped with Dy³⁺ & Eu³⁺ nanoparticle has been synthesized by solution combustion method. The formation of the compounds has been checked by X-ray diffraction method. The crystallite/particle size has been measured using Scherrer formula as well as by transmission electron microscopy which show that the size of the particles are in the nanorange. The frequency and temperature dependent variation of impedance Z*, dielectric constant (ε′), dielectric loss (ε″) and AC conductivity (σ) of Y₂O₃: Dy³⁺ & Eu³⁺ nanoparticles were also measured. The real and imaginary part of complex impedance makes semicircle in the complex plane. The center of semicircle arc is found to be shifted toward higher value of real part of impedance with increasing temperature. This indicates that the conductivity of the material increases with the increase in temperature. Cole–Cole plots demonstrate that the dielectric relaxation process occurs in the material. The AC conductivity (σ _AC) increases with the increase in temperature within the frequency range of 10³–10⁷ Hz confirming the hopping of the electrons in the conduction process. The value of impedance decreases sharply with increasing frequency and attains minimum value after 10⁵ Hz at all temperatures.     

Influence of lithium potassium zirconate nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) films

We investigated the influence of lithium potassium zirconate (LiKZrO₃) nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) (PVA) films. PVA/LiKZrO₃ nanocomposite films were prepared by casting of aqueous solutions with varying LiKZrO₃ content (0.5, 1.0, and 2.0 wt.%). The dielectric constant (ε′), dielectric loss (ε″), AC conductivity (σ_ac), dielectric loss tangent (tan δ), and electric modulus (M′ and M″) of the nanocomposite films were measured over a range of frequencies at ambient temperature. The results show increases in σ_ac and M′ with frequency, whereas ε′, ε″, and tan δ decreased with increasing frequency. The films were also characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. DSC and XRD revealed the nature of LiKZrO₃ nanoparticle interaction with the PVA matrix. TGA analysis revealed an increase in thermal stability of the nanocomposites with increasing nanoparticle concentration. Scanning electron microscopy confirmed uniform dispersion of LiKZrO₃ nanoparticles in the PVA matrix.     

Dielectric characteristics and thermal behaviour of terbium fumarate heptahydrate crystals

Dielectric properties, ac conductivity and thermal characteristics of terbium fumarate heptahydrate crystals grown by gel diffusion method have been carried out. The real part of dielectric constant, dielectric loss and ac conductivity of the material have been measured as a function of temperature and frequency of the applied electric field. Dielectric constant, dielectric loss and ac conductivity of the title compound were systematically investigated, showing a hump at about 85 °C, which could be attributed to water molecules in the crystal boundary. The dielectric anomaly exhibited by the material has been correlated with its thermal behaviour. The ac conductivity of the material obeys the Jonscher's power law relation; σ(ω) = σ_o + Aω^s, with the temperature dependent power exponent s < 1. The ac conductivity of the compound has been found to increase with the increase in frequency. The material is suggested to show protonic conduction. The non-isothermal kinetics was used to evaluate the activation energy for the dehydration step of thermal decomposition of terbium fumarate heptahydrate by using the Coats–Redfern integral method.     

On autoionization and pH of liquid water

The ionization constant of water K_w (or pH) is currently determined on the proton conductivity σ₀ which is measured at frequencies lower than 10⁷ Hz. We develop the idea that the high frequency conductivity σ_∞ (~10¹¹ Hz), rather than σ₀ represents a net proton dynamics in water. We count the concentration c of the H₃O⁺ and OH^– ions from σ_∞ to find c to be not dependent on temperature. We conclude that spontaneous ionization of H₂O molecules is not essential in water electrodynamics; the common K_w reflects the thermoactivation of the H₃O⁺ and OH^– ions from the potential of their interaction; the lifetime of a target water molecule does not exceed parts of nanosecond.     

Mn2+doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal

Undoped and Mn²⁺-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan?δ) and ac conductivity (σ_ac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1–100?kHz, and temperature, in the range 300–580?K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan?δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σ_ac) and tan?δ along the polar axis of KZC increased significantly with increasing Mn²⁺ content while ε decreased. σ_ac changed with frequency according to a power law of the form σ_ac?=?f? ^s where 0.15<s<1.27. A linear decrease of ε and tan?δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn²⁺-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples.     

Frequency Dependence of the Dielectric Loss Angle in Disordered Semiconductors in the Terahertz Frequency Range

Frequency dependence of the real part of the conductivity σ₁(ω) in the region of the transition from almost linear (s < 1) to quadratic (s ≈ 2) can indicate a change in the conduction mechanism (the transition from the variable-range to the fixed-range hopping with increasing frequency); in this case, the sharpness of the change in the slope of the frequency characteristic is related to the dependence of the preexponential factor of the resonance integral on the intercenter distance in the pair. The frequency dependence of the imaginary part of the conductivity σ₂(ω) has no kink in the vicinity of the transition frequency ωcr, remaining almost linear. A large dielectric loss angle |cotγ| = |σ₂|/σ₁ can indicate that the imaginary part of the conductivity at ω < ω_cr is defined by the larger zero-phonon contribution in σ₂^res the region of weak variation in the loss angle γ(ω), which significantly exceeds the relaxation contribution σ₂^res.     

Specific features of the dielectric spectrum of CaCu3Ti4O12 in the low-frequency range

The dielectric spectra of CaCu₃Ti₄O₁₂ ceramics with giant values of the dielectric constant have been presented. The spectrum exhibits Debye dispersion with an activation energy of 0.075 eV in the high-frequency range of 10⁶–10⁷ Hz, and a characteristic plateau has been seen in the frequency dependence of the dielectric constant in the range of 10⁴–10⁵ Hz. A considerable increase in the loss factor ?″ has been observed in the low-frequency part of the spectrum and a capacitive-to-inductive impedance transition has been revealed in some samples at a frequency below 10^?2 Hz. The causes of this transition have been discussed.     

Dielectric relaxation in vanadium phosphate glasses

An asymmetric distribution of relaxation times has been inferred from an increase in the Cole-Cole distribution parameter α with increasing values of ωτ in 62% v₂O₅–38% P₂O₂ glass. The conventional Debye type relaxation loss peaks in the frequency range 10²–10⁵ Hz are observed in this sample above 85°K. The extrapolated values of dielectric constant and relaxation time below 100°K seem unexpectedly large while the high temperature extrapolated values of ?' are close to ?_∞ as expected. Probably the conventional dielectric loss peaks are observed only above a critical temperature at which the carriers gain sufficient energy to be excited to the conduction band edge. Below this temperature hopping of carriers within kT of the Fermi level may dominate and conventional Debye type dielectric loss peaks may lose their significance as envisaged in the models of frequency dependent ac conductivity.