High Temperature Structural,Dielectric, and Ion Conduction Properties of Orthorhombic InVO4

Orthorhombic InVO₄ was prepared by solid‐state reaction method and characterized by powder X‐ray diffraction and scanning electron microscopy. The frequency‐dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature.     

Dielectric relaxation and electrical conductivity in Ca5Nb4TiO17 ceramics

The temperature dependence of dielectric properties and electrical conduction of Ca₅Nb₄TiO₁₇ ceramics were characterized in a broad temperature range. A dielectric anomaly with strong frequency dispersion was detected in the temperature range 700–1010 °C. This dielectric relaxation could be almost removed completely by annealing in an oxidizing atmosphere. Complex impedance analysis confirmed the electrical inhomogeneity of the ceramics with different contributions from the bulk and grain boundaries. This suggests that the main mechanism for the observed relaxation is the Maxwell–Wagner polarization. ac conductivity results revealed the variation of conduction mechanism with increasing temperatures from localized hopping to long-range motion of the doubly ionized oxygen vacancies.     

Structural and dielectric properties of CuO nanoparticles

The DC conduction and dielectric behaviour of copper oxide nanoparticles prepared by sol-gel method and sintered at 950 °C were studied in the temperature range of 200–526 K. The formation of single phase monoclinic CuO was confirmed by x-ray diffraction. Chemical composition of the CuO ceramic was investigated with X-ray photoelectron spectroscopy (XPS) technique. Although XRD analysis shows the formation of single phase CuO, XPS spectra revealed the presence of Cu³⁺ and Cu²⁺. Deviation from linearity ln (σ_DC) vs. 1/T plot at ~390 K was observed, which indicates that DC conduction in the CuO pellet is dominated by two different conduction mechanisms. The results obtained on AC conductivity indicate that AC conduction mechanism could be well explained by the multihopping model at low frequencies, while high frequency AC conductivity data can be described by small polaron tunnelling model. The dielectric relaxation mechanism in the CuO pellet was studied by impedance spectroscopy. It was found that while dielectric constant is an increasing function of temperature, it decreases with increasing frequency. The obtained impedance spectra indicated that the grain boundary effects and intergranular activities play a crucial role on the dielectric relaxation processes.     

Dielectric behavior dependence on temperature and Cr-doping contents of Aurivillius Bi5Ti3FeO15 ceramics

The dielectric behavior of Cr-doped Bi₅Ti₃FeO₁₅ (BTFCO) ceramics was systemically studied by temperature-dependent dielectric/impedance spectroscopy from 200 K to 400 K. Two dielectric relaxation processes were found in grain interiors of the BTFCO ceramics. Both of them showed similar activation energy. This usually brings a great challenge to discern the different mechanisms of the conductivity and/or dielectric responses in Fe–Cr-based materials; nevertheless the origins of the two relaxations were unambiguously determined by adjusting the Cr doping contents. One relaxation at high temperature region was proposed to be associated with the localized electron hopping between Fe³⁺ and Fe²⁺, whereas another one at lower temperatures was assigned to the localized hole transfer between Cr³⁺ and Cr⁶⁺ inside the grains. Moreover, the transition temperature between the two relaxations showed a nearly linear reducing trend with the Cr-doping content.     

Impedance spectroscopic behaviour of spark plasma sintered nanocrystalline scandia stabilized zirconia (SSZ)

Nanocrystalline scandia (Sc₂O₃) doped zirconia was prepared by dissolution and co-precipitation method. The formation of the nanostructured nearly cubic phase has been observed from transmission electron microscope and X-ray diffraction studies. Spark plasma sintering retains the nano/submicrograin structure. The frequency dependent conductivities were measured in the frequency range from 100 Hz to 1 MHz and at temperatures 300–800 K. The impedance diagram shows the grain interior and grain boundary resistance contributions. The frequency dependent conductance spectra show the DC plateau (at low frequency region) and dispersive region suggesting the correlated hopping motion of ions. The dielectric-loss spectra suggest the presence dielectric relaxation, which is related to enthalpy of ion hopping. Characteristic hopping frequencies were calculated and appear to be related to the thermally activated ion hoping process.     

Frequency and Temperature‐Independent Electrical Transport Properties of 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass‐Ceramics

The temperature (300–973 K) and frequency (100 Hz–10 MHz) response of the dielectric and impedance characteristics of 2BaO‐0.5Na₂O–2.5Nb₂O₅–4.5B₂O₃ glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100 Hz–10 MHz) and temperature (300–600 K). The temperature coefficient of dielectric constant was 8 ± 3 ppm/K in the 300–600 K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal‐glass interface, leading to a high value of effective dielectric constant especially for the samples heat‐treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (P_r) increased with the increase in crystallite size.     

Near Constant Loss Dielectric Response in 2Bi2O3–B2O3 Glasses

Electrical conduction and relaxation phenomena in bismuth borate glasses in the composition 2Bi₂O₃–B₂O₃ (Bi₄B₂O₉) were investigated. Dielectric studies carried out on these glasses revealed near constant loss response in the 1 kHz–1 MHz frequency range at moderately high temperatures (300–450 K) associated with relatively low loss (tan δ = 0.006) and high dielectric constant (ε_r′ = 37) at 1 kHz, 300 K. The variation in AC conductivity with temperature at different frequencies showed a cross over from near constant loss response characterized by local ion vibration within the potential well to universal Jonscher's power law dependence triggered by ion hopping between potential wells or cages. Thermal activation energy for single potential well was found to be 0.48 ± 0.05 eV from cross over points. Ionic conduction and relaxation processes were rationalized by modulus formalism. The promising dielectric properties (relatively high ε_r′ and low tan δ) of the present glasses were attributed to high density (93% of its crystalline counterpart), high polarizability, and low mobility associated with heavy metal cations, Bi³⁺.     

Dielectric relaxation and ac conductivity in magnetoelectric YCrO3 ceramics: A temperature dependent impedance spectroscopy analysis

Here, we report on the temperature and frequency dependent electrical conduction and dielectric behaviour of YCrO₃ ceramics. Dielectric studies reveal a peak in the dielectric constant ～230?K, suggesting presence of spin-charge coupling. Also, an additional broad peak found at ～450?K is reminiscent of a relaxor like behaviour for YCrO₃, attributed to a diffused phase transition. The nature of dc conductivity is of Arrhenius type and shows an abrupt change in the activation energy at ～230?K and ～450?K. The activation energy suggests that the polaronic hopping mechanism stabilizes at low temperature while, at higher temperatures, the process is associated with the diffusion of double ionized oxygen vacancies. However, ac conductivity suggests that the overlapping large polaron tunnelling conduction mechanism drives the ac conduction below 300?K and above 300?K, the conduction behaviour is consistent with the correlated barrier hopping conduction mechanism.     

High-conducting Bi4V2−xFexO11-δ ceramics containing Fe2O3 nanocrystals: Structure and properties

The topography, structure, thermal, magnetic, and electrical properties of Bi₄V_2?xFe_xO_11-δ ceramics substituted with x = 0.5 and 0.7 Fe were studied. The microscope analysis showed the presence of iron-rich nanocrystals formed on the Bi-Fe-V-O grains. The X-ray diffraction studies confirmed that grains are built mostly of tetragonal Bi₄V_1.5Fe_0.5O_10.5 phase. Thermal properties analysis showed an order-disorder type γ ? γ? phase transition at a temperature of around 916 K, pronounced in samples doped with x = 0.5 Fe. The magnetic anomaly was observed in ceramics doped with x = 0.7 Fe which was assigned to Morin transition of Fe₂O₃. The conductivity was measured over a wide frequency range from 10 mHz to 1 MHz and at a wide temperature range from 373 to 923 K, using impedance spectroscopy. The D.C. conduction process was due to oxygen vacancies hopping while at low temperatures electron holes hopping is also possible.     

Oxygen Ion Conduction in Bulk and Grain Boundaries of Nominally Donor‐Doped Lead Zirconate Titanate (PZT): A Combined Impedance and Tracer Diffusion Study

Oxygen ion conduction in Nd³⁺‐doped Pb(Zr_xTi_1?x)O₃ (PZT) was investigated by impedance spectroscopy and ¹⁸O‐tracer diffusion with subsequent secondary ion mass spectrometry (SIMS) analysis. Ion blocking electrodes lead to a second relaxation feature in impedance spectra at temperatures above 600°C. This allowed analysis of ionic and electronic partial conductivities. Between 600°C and 700°C those are in the same order of magnitude (10^?5–10^?4 S/cm) though very differently activated (2.4 eV vs. 1.2 eV for ions and electron holes, respectively). Oxygen tracer experiments showed that ion transport mainly takes place along grain boundaries with partly very high local ionic conductivities. Numerical analysis of the tracer profiles, including a near‐surface space charge zone, revealed bulk and grain‐boundary diffusion coefficients. Calculation of an effective ionic conductivity from these diffusion coefficients showed good agreement with conductivity values determined from impedance measurements. Based on these data oxygen vacancy concentrations in grain boundary and bulk could be estimated. Annealing at high temperatures caused a decrease in the grain‐boundary ionic conductivity and onset of additional defect chemical processes near the surface, most probably due to cation diffusion.     

Oxygen‐Vacancy‐Related High Temperature Dielectric Relaxation in (Pb1−xBax)ZrO3 Ceramics

(Pb_1?xBa_x)ZrO₃ (x = 0, 0.025, 0.05, 0.075, 0.1) ceramics were synthesized by a traditional solid‐state reaction method, and the pure phase was obtained of all sintered samples. For all compositions, substitution of Pb²⁺ by Ba²⁺ reduced the phase transition temperature of antiferroelectric to ferroelectric and Curie temperature. Polarization–electric field hysteresis loops were conducted and typical ferroelectric hysteresis loops were observed in higher temperature range. Impedance and dielectric measurements were studied on the high temperature relaxation. Relaxation behavior could be suppressed after annealing treatment in oxygen atmosphere. Value of activation energy calculated from impedance was lower than that calculated from conduction measurements. It was concluded that short‐range hopping of oxygen vacancy contributes to the dielectric relaxation and long‐distance movement of doubly ionized oxygen vacancies contributes to the conduction.     

Broadband impedance spectroscopic characterization of PbTiO3 crystal grown by spontaneous crystallization from molten oxides

Tetragonal lead titanate PbTiO₃ single crystals were grown by spontaneous crystallization from a lead and boron oxide flux and investigated by impedance spectroscopy in the broadband frequency range (10⁻³–5×10⁶ Hz) along the crystallographic a and c axes at room temperature.Three polarization relaxation modes as well as electric conductivity processes were revealed. In the ultralow frequency range (<10 Hz), the relaxation processes were assigned to the electrode and the ferroelectric domains polarizations. In the high frequency range (10⁵ Hz), the relaxation process arises from the crystal lattice polarizations. The electric conduction of the investigated crystals is determined by two fundamental effects – ionic and hopping conductivities. In addition, the anisotropies of relative dielectric constant (300) as well as DC conductivity (1.8×10⁻⁹ S/m) were estimated.     

Dielectric analysis of α‐relaxation process of chlorinated poly(vinyl chloride) stabilized with nitro‐phenyl maleimide

Nitro‐phenyl maleimide (NPM), is the organic stabilizer for poly (vinyl chloride) (PVC), has been investigated as thermal plasticization for rigid chlorinated poly (vinyl chloride) (CPVC). Dielectric relaxation of CPVC stabilized with 10 wt% of NPM has been studied in temperature and frequency ranges of 300–450 K and 10 kHz–1 MHz, respectively. An analysis of the dielectric constant, ε′ and dielectric loss index, ε″, was performed assuming a plasticization effect of NPM molecules. The plasticization effect of NPM molecules was confirmed by the behavior of the dielectric modulus M′ and M″ spectra. A clear dielectric α‐relaxation process has been obtained in the studied temperature range. The results showed that NPM reduce the glass transition temperature, T_g, of CPVC by about 20 K. This effect has been assigned to the plasticization effect of NPM. At lower temperatures, dielectric modulus spectra reveal that there is a role of the effect of the electrode polarization in the relaxation process. The behavior AC conductivity, σ_ac, indicated that the conduction mechanism in all CPVC samples is hopping type conduction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Dielectric and electric relaxations induced by the complex defect clusters in (Yb+Nb) co‐doped rutile TiO2 ceramics

The effect of the Yb+Nb substitution for Ti on the microstructure, crystal structures, and dielectric properties of (Yb_1/2Nb_1/2)_xTi_1?xO₂ (0.01≤x≤0.1) ceramics is investigated in this study. The results reveal that the solid solubility limit of the (Yb_1/2Nb_1/2)_xTi_1?xO₂ ceramics is x=0.07, and the average grain sizes considerably decrease from 12 μm to 6 μm with x increasing from 0.01 to 0.1. Three types of dielectric relaxations are observed at temperature ranges of 10‐30 K, 80‐180 K, and 260‐300 K, caused by the electron‐pinned defect dipoles, polaron hopping, and interfacial polarizations, respectively. The conduction mechanism changes from nearest‐neighbor‐hopping to polaron hopping mechanism, which is confirmed by ac conductivity measurements. The present work indentifies the correlation between the colossal permittivity and polaron hopping process in the titled compound.     

Li+ ion conduction mechanism in poly (ε-caprolactone)-based polymer electrolyte

In this work, solid polymer electrolytes based on poly(?-caprolactone) (PCL) with lithium bis(oxalato)borate as a doping salt were prepared by solution cast technique using DMF as a solvent. The electrical DC conductivity and dielectric constant of the solid polymer electrolyte samples were investigated by electrochemical impedance spectroscopy over a frequency range from 50 Hz to 1 MHz. It was found that the DC conductivity increased with increase in the salt concentration to up to 4 wt% and thereafter decreased. Dielectric constant versus salt concentration was used to interpret the decrease in DC conductivity with increase in salt concentration. The DC conductivity as a function of temperature follows Arrhenius behavior in low temperature region, which reveals that ion conduction occurs through successful hopping. The curvature of DC conductivity at high temperatures indicates the contribution of segmental motion to ion conduction. High values for dielectric constant and dielectric loss were observed at low frequencies. The plateau of dielectric constant and dielectric loss at high frequencies can be observed as a result of rapid oscillation of the AC electric field. The HN dielectric function was utilized to study the dielectric relaxation. The experimental and theoretical data of dielectric constant are very close to each other at low temperatures. At high temperatures, the simulated data are more deviated from the experimental curve of dielectric constant due to the dominance of electrode polarization. The non-unity of relaxation parameters (α and β) reveals that the relaxation processes in PCL-based solid electrolyte is a non-Debye type of relaxation.     

High‐Temperature Dielectric Relaxation in Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals

We reported the dielectric properties of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ single crystal in the temperature range of 300–1073 K and the frequency range of 100 Hz–10 MHz. Our results showed the coexistence of both true‐ and pseudo‐relaxor behaviors in the crystal. The true relaxor behavior related to the paraelectric‐ferroelectric phase transition occurs at~423 K. The pseudo‐relaxor behavior appearing at~773 K was found to be related to oxygen vacancies. Further investigation reveals that the pseudo‐relaxor behavior has fine structure: it contains two oxygen‐vacancy‐related relaxation processes. The low‐temperature relaxation process is a dipolar relaxation created by the hopping motions of the oxygen vacancies, and the high‐temperature relaxation process is a Maxwell‐Wagner relaxation caused by the sample/electrode contacts.     

Structural and physical characteristics of Au2O3-doped sodium antimonate glasses – Part II electrical characteristics

In continuation of our earlier investigations on structural and physical characteristics of Au₂O₃-doped sodium antimonate glass-ceramics (Part-1), in this part we have investigated the influence of gold ions on electrical characteristics of the Na₂O–Sb₂O₃: Au₂O₃ glass-ceramics. The study contains the results of quantitate investigations on dielectric properties, impedance spectra and A.C. conductivity in larger ranges of continuous frequencies (4 Hz-8 MHz) and temperatures (300-630 K). The variations exhibited by dielectric parameters with temperature and also with frequency were discussed in terms of various polarization mechanisms. The observed dielectric relaxation effects were analyzed using pseudo Cole-Cole plot method and the analysis indicated spreading of relaxation times for dipoles. A.c. conductivity and also d.c. conductivity were found to decrease (to three orders of magnitude) with increase in Au₂O₃ concentration upto 0.1 mol%. The decrement is ascribed to the increasing concentration of Sb⁵⁺ ions that were predicted to participate in the glass network forming with SbO₄ units. Even though, both ionic and polaronic contributions are possible for conduction in the studied material, quantitative analysis of these results indicated that the polaronic conduction (due to intervalence transfer between Sb³⁺ ↔ Sb⁵⁺ and Au⁰ ↔ Au³⁺) is prevalent. The results have also suggested that there is a gradual decrement in the ionic component with increase in Au₂O₃ concentration. Variation in σ_ac in the low-temperature region could satisfactorily be explained using quantum mechanical tunneling (QMT) model. Analysis of the results of d.c. conductivity indicated that the small polaron hoping (SPH) model is valid, especially in a high-temperature region while the low temperature part of d.c. conductivity is analyzed based on variable range hopping (VRH) model. Overall, the increase in Au₂O₃ dopant concentration in the studied glass-ceramics caused a decrement in the magnitude of the conductivity or increase in the insulating strength of the material.     

Structural and functional properties of sol-gel synthesized and microwave heated Pb0.8 Co0.2-zLazTiO3 (z = 0.05–0.2) nanoparticles

The present work reports the effect of La-substitution on structural and functional properties of lead cobalt titanate (PCT) perovskite structure as a function of variation of Co-content. The sol-gel synthesized and microwave heated Pb_0.8 Co_0.2-zLa_zTiO₃ (z?=?0.05, 0.1, 0.15 & 0.2) (PCLT) nanoparticles showed the presence of complete cubic phases while few were noted to be tetragonal lead titanate (PT) phases. The surface morphology was examined by field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). The HRTEM revealed fibers like nanoparticles at z?=?0.15 and 0.2. The Fourier transform infrared spectra attributed the presence of metal oxide bonds. Furthermore, the wide optical band gap energy (E_op) was acquired to be changing from 2.32 to 3.20?eV. In addition, the electrical parameters such as dielectric constant (ε'), dielectric loss (ε"), ac & dc-electrical conductivity (σ_ac & σ_dc), complex dielectric modulus (M^*) and complex impedance (Z^*) were studied as a function of frequency (f) and composition. Using power law fitting, the σ_dc values were determined. The z?=?0.15 content exhibited high σ_dc of ~ 2.51?×?10^?7 S/cm among all compositions. Besides, the results expressed the existence of short range and long range hopping conduction regions in dielectric modulus spectra. The Nyquist plots were drawn to elucidate the electrical conduction and relaxation mechanism. Later on, ferroelectric hysteresis loops were recorded for z?=?0.05–0.2.     

AC conductivity,electric modulus analysis and electrical conduction mechanism of RbFeP2O7 ceramic compound

In this work, the diphosphate compound, RbFeP₂O₇, was prepared by the conventional solid-state reaction. The X-ray diffraction pattern revealed that the sample presents a single phase, that crystallizes in the monoclinic structure with a P2₁/C space group. Impedance analysis was performed using the equivalent circuit model, and, it indicated the presence of intra- and inter-granular contribution. Furthermore, the electrical conductivity, the dielectric properties and the relaxation behavior of this material were studied in detail using the impedance spectroscopy technique, in a frequency ranging from 200 Hz to 5 MHz at several temperatures. The temperature dependency of frequency exponent 's' shows that the correlated barrier-hopping model (CBH) is the most responsible mechanism for AC conduction in the investigated compound. In terms of CBH model, the values of maximum barrier s height, the hopping distance and the density of localized states are determined and discussed. A correlation between electrical and structural properties was also discussed.     

Dielectric Tunability,Dielectric Relaxation,and Impedance Spectroscopic Studies on (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 Lead‐Free Ceramics

Dielectric and impedance spectroscopies were employed to study the electrical behavior of (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (abbr. BCTZ) lead‐free ceramic. The dielectric properties versus dc bias electric field experiment revealed high dielectric tunability (> 65%) as well as figure of merit (> 27) at 10 kHz and room temperature. At elevated temperature range, a dielectric loss peak was observed and verified to be correlate of oxygen vacancy relaxation. The impedance spectra studies indicate that the ceramic is a mixed ionic conductor of p‐type nature at the paraelectric phase and, the grain and total conductivity at 600°C reaches 6.0 × 10^?5 and 2.0 × 10^?5 S/cm, respectively.