Study of complex impedance spectroscopic properties of the KFeP2O7 compound

The KFeP₂O₇ compound was prepared by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction. The AC electrical conductivity and the dielectric relaxation properties of this compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 200 Hz–5 MHz and 553–699 K, respectively. Both impedance and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies Eg?=?0.94 (3)?eV and Egb?=?0.89 (1)?eV. The grain-and-grain boundary conductivities at 573 K are 1.07?×?10^?4 and 1.16?×?10^?5 (Ω^?1 cm^?1). The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation describes the same mechanism at various temperatures. The near value of the activation energies obtained from the equivalent circuit, conductivity data, and analysis of M″ confirms that the transport is through ion hopping mechanism.     

Li<Superscript>+</Superscript> ion conductivity and transport properties of LiYP<Subscript>2</Subscript>O<Subscript>7</Subscript> compound

A lithium yttrium diphosphate LiYP₂O₇ was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. The infrared and Raman spectrum of this compound was interpreted on the basis of P₂O₇ ^4? vibrations. The AC conductivity was measured in the frequency range from 100 to 10⁶ Hz and temperatures between 473 and 673 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. The Cole–Cole diagram determined complex impedance for different temperatures. The angular frequency dependence of the AC conductivity is found to obey Jonscher’s relation. The temperature dependence of σ _AC could be described in terms of Arrhenius relation with two activation energies, 0.87 eV in region I and 1.36 eV in region II. The study of temperature variation of the exponent(s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the correlated barrier hopping (CBH) model in region I (T < 540 K) and non-overlapping small polaron tunneling (NSPT) model in region II (T > 540 K). The near value of activation energies obtained from the equivalent circuit and DC conductivity confirms that the transport is through ion hopping mechanism dominated by the motion of the Li⁺ ion in the structure of the investigated material.     

Electrical characterization of porous La-doped BaSnO<Subscript>3</Subscript> using impedance spectroscopy

A few compositions in the system Ba_1???x La _x SnO₃ (x?=?0.00, 0.01, 0.05, and 0.10) have been synthesized via the solid state ceramic route. The synthesized powders have been characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, Fourier transformation infrared, thermogravimetrical analysis, and differential thermal analysis techniques. The powder X-ray diffraction pattern of the samples confirms the formation of a single-phase solid solution only up to 0.50?≤?x. It was found that all the samples have a cubic crystal structure. The electrical properties of La-modified BaSnO₃ were studied using ac impedance spectroscopy technique over a wide range of temperatures (50–650 °C) in the frequency range of 10 Hz–13 MHz. The complex impedance plots above 300 °C show that total impedance is due to the contributions of grain and grain boundaries. The resistance of these contributions has been determined. Variation of these resistances with temperature shows the presence of two different regions with different slopes. The nature of the variation of conductivity of the grain and grain boundaries is different in different regions. Based on the value of activation energy, it is proposed that conduction via hopping of doubly ionized oxygen vacancies (V_O ^??) is taking place in the temperature region of 300–450 °C, whereas in the temperature region of 450–650 °C, it is due to proton, i.e., OH^? ions, hopping.     

CO(III)–NI(II) double substituted bismuth vanadate: synthesis,phase stabilization,and structural and electrical characterization

Samples of Co–Ni double substituted bismuth vanadate, BICO_0.20?x NI _x VOX (Bi₄Co_0.20???x ^(III)Ni _x ^(II)V_1.8O_{10.8???(x/2)???δ} ;0?≤?x?≤?0.20) were synthesized by standard solid state reactions. The influence of Ni substitution for Co on phase stabilization and oxide-ion performance have been investigated using X-ray powder diffraction, differential thermal analysis, and AC impedance spectroscopy. The high conducting γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380 °C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (～2.56?×?10^?4 S cm^?1 at 300 °C) was observed for the composition with x?=?0.13. However, a good agreement was generally found between the values of electrical conductivity and corresponding activation energies of conduction.     

Experimental and theoretical study of AC electrical conduction mechanisms by NSPT model of LiNa<Subscript>3-x</Subscript>Ag<Subscript>x</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.2 and 0.6) ceramic compounds

New pyrophosphate of ceramic compounds LiNa_3-xAg_xP₂O₇ (x = 0.2 and 0.6) is synthesized by a solid-state method. All the compounds crystallize in the orthorhombic lattice with space group C222₁. The infrared spectra of these compounds show characteristic bands due to a P₂O₇ group. The two semicircles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in these materials. The frequency independent conductivity of these compounds shows Arrhenius-type behavior. The activation energies have been calculated at the levels of impedance, electric modulus studies, and DC conductivity which suggest that the conductions are ionic in nature. The conductivity increases with an increase in Ag substitution. In order to determine the conduction mechanism, the AC conductivity and its frequency exponent have been analyzed in this work by a theoretical model based on quantum mechanical tunneling: the non-overlapping small polaron tunneling model (NSPT) is confirmed for x = 0.2 and x = 0.6. The conduction mechanism is studied with the help of Elliot’s theory, and the Elliot’s parameters are determined.     

Impedance spectroscopy of vanadium modified BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

In recent years a wide range of Aurivillius layered materials have been introduced. These novel materials are produced in many various forms such as fibers, thin films as well as bulk by using a number of processing routes. As advanced materials they are they have many interesting properties which include a number of useful electrical properties related to separated grain and grain boundary conductivity, impedance, activation energies, etc. In this paper these properties are described and discussed in detail. The electrical properties of the vanadium doped BaBi₂Nb₂O₉ ceramic was measured over a wide range of temperatures by impedance spectroscopy (IS). The separated grain activation energy, calculated from Arrhenius characteristics at temperatures between room temperature and 600 °C, was 1 eV for 0 at.% of vanadium dopant and 1.2 eV for 10 at.%, whereas the activation energies in the grain boundary region were 0.97 and 1.15 eV, respectively. The obtained results suggest the significant role of vanadium dopant, causing ordering the crystalline structure.     

Impedance spectroscopy analysis of Li<Subscript>2</Subscript>SnO<Subscript>3</Subscript>

In this work, Li₂SnO₃ has been synthesized by the sol–gel method using acetates of lithium and tin. Thermogravimetric analysis (TGA) has been applied to the precursor of Li₂SnO₃ to determine the suitable calcination temperature. The formation of the compound calcined at 800 °C for 9 h has been confirmed by X-ray diffraction (XRD) analysis. The Li₂SnO₃ is then pelletized and electrically characterized by using electrochemical impedance spectroscopy (EIS) in the frequency range from 50 Hz to 1 MHz. The complex impedance spectra clearly show the dominating presence of the grain boundary effect on electrical properties whereas the complex modulus plots reveal two semicircles which are due to the grain (bulk) and grain boundary. The spectra of imaginary parts of both impedance and modulus versus frequency show the existence of peaks with the modulus plots exhibiting two peaks that are ascribed to the grain and grain boundary of the material. The peak maximum shifts to higher frequency with an increase in temperature and the broad nature of the peaks indicates the non-Debye nature of Li₂SnO₃. The activation energy associated with the dielectric relaxation obtained from the electrical impedance spectra is 0.67 eV. From the electric modulus spectra, the activation energies related to conductivity relaxation in the grain and grain boundary of Li₂SnO₃ are 0.59 and 0.69 eV, respectively. The conductivity–temperature relationship is thermally assisted and obeys the Arrhenius rule with the activation energy of 0.66 eV. The conduction mechanism of Li₂SnO₃ is via hopping.     

Electrical properties of novel Li4.08Zn0.04Si0.96O4 ceramic electrolyte at high temperatures

Novel Li_4.08Zn_0.04Si_0.96O₄ electrolyte was synthesized by citric acid-assisted sol–gel method. The compound was studied by X-ray diffraction and complex impedance spectroscopy in the frequency range from 10 Hz to 10 MHz and temperature range from 573 to 773 K. The conductivity–frequency spectra exhibited two regions of conductivity dispersion related to Li⁺ ion transport in the bulk and grain boundaries. The activation energy of the bulk conductivity was found to be equal to the activation energy of relaxation frequency in the bulk. This indicated that the increase in conductivity with temperature was due to the increase in ion mobility while the number of charge carrier concentration was found to be constant with selected temperature range. The observation was in agreement with the calculated charge carrier concentration and ion mobility derived from conductance spectra, σ _ac(ω)?=?σ _o ?+?Aω ^α .     

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.     

Effect of Zn substitution on the electrical properties of Bi2Co0.1V0.9O5.35 synthesized by sol-gel method

Samples of Bi₂V_0.9Co_0.1-xZn_xO_5.35, 0.02 ≤ x ≤ 0.08 with layered Aurivillius structure were synthesized successfully by sol-gel citrate method. Structural and electrical characterization of compositions has been investigated by X-ray diffraction, thermogravimetric analysis–differential scanning calorimetric (TGA–DSC) analysis and AC impedance spectroscopy. The tetragonal γ phase has been observed for all investigated samples. The AC impedance response of samples has been measured in the frequency range of 20 Hz to 1 MHz. The impedance for pellets decreases as thermal energy increases. The contribution of grain to the conduction process is more than that of grain boundary. The ionic conductivity and dielectric permittivity are found to be composition-dependent and increase with increasing Zn concentration. The maximum electrical conductivity observed for the composition x = 0.08 is σ = 4.51 × 10^?4 S cm^?1 at 300 °C.     

Frequency–temperature response of CaBi4Ti4O15 ceramic prepared by soft chemical route: Impedance and modulus spectroscopy characterization

Polycrystalline CaBi₄Ti₄O₁₅ ceramic has been prepared through a modified chemical reaction technique. Room temperature X-ray diffraction (XRD) analysis shows the formation of a single phase orthorhombic perovskite structure. Simultaneous analysis of the complex impedance (Z1), and electric modulus (M1) spectroscopy was carried in the temperature range of 100–850 °C. The dielectric relaxation is found to be of non-Debye type. The Nyquist plot shows the negative temperature coefficient of resistance type behavior. Two different conduction mechanisms are may be due to: (a) the dielectric relaxation processes due to localized conduction associated with oxygen vacancy; and (b) the non-localized conduction corresponding to long range conductivity associated with extrinsic mechanisms fundamentally associated due to the chemical inhomogeneity caused due to the difference in the ionic environment of Ca²⁺ and Bi³⁺ and their sharing in the A site of perovskite and [Bi₂O₂]²⁺ slabs. Different conductivity components are recognized inside the grain: long range dc conductivity at low frequency region, a capacitive behavior at higher frequencies, and a universal power law behavior in an intermediate-frequency region where grain boundary contributions are neglected.     

Electrical transport characteristics of ZnO–Bi2O3–B2O3 glasses

Optically clear glasses in the ZnO–Bi₂O₃–B₂O₃ (ZBBO) system were fabricated via the conventional melt-quenching technique. Dielectric constant and loss measurements carried out on ZBBO glasses unraveled nearly frequency (1 kHz–10 MHz)-independent dielectric characteristics associated with significantly low loss (D?=?0.004). However, weak temperature response was found with temperature coefficient of dielectric constant 18?±?4 ppm °C^?1 in the 35–250 °C temperature range. The conduction and relaxation phenomena were rationalized using universal AC conductivity power law and modulus formalism respectively. The activation energy for relaxation determined using imaginary parts of modulus peaks was 2.54 eV which was close to that of the DC conduction implying the involvement of similar energy barriers in both the processes. Stretched and power exponents were temperature dependent. The relaxation and conduction in these glasses were attributed to the hoping and migration of Bi³⁺ cations in their own and different local environment.     

The analysis of the electrical properties of BLT ceramics fabricated from sol-gel derived powders

The (Ba_xLa_1?x)Ti_1?x/4O₃ (BLT,0.001 ≤ x ≤ 0.005) amorphous gel was prepared by sol-gel process. The electricalproperties of obtained materials has been investigated by impedance spectroscopy. Detailedanalysis of impedance spectra allowed to propose an adequate equivalent circuit, whichdescribed the electric properties of discussed materials very well. Basing on the obtainedcircuits and the fitting procedure the grain and grain boundary resistivity was determinedas a function of temperature and La concentration. With increase of La admixture thecontribution of grain and grains impedance to the bulk impedance changes. It was foundthat the small amount of La additive decreases the blocking factor of the grain boundaryin the temperature range 600–850 K, whereas the amount of La on the level of 0.4–0.5 mol.%causes the sharp increase of the mentioned factor. The fact may be attributed to adecrease of grain activation energy and increase of the grain boundary one.     

AC and DC conductivity study of LiH<Subscript>2</Subscript>PO<Subscript>4</Subscript> compound using impedance spectroscopy

The lithium dihydrogen phosphate LiH₂PO₄ has been investigated by X-ray powder diffraction, scanning electron microscopy (SEM), and electrical impedance spectroscopy. The Rietveld refinements based on the XRD patterns show that the compound is crystallized in the orthorhombic system with Pna2₁ space group, and the refined unit cell parameters are a = 6.2428 Å, b = 7.6445 Å, and c = 6.873 Å. The electrical properties were studied using complex impedance spectroscopy as a function of frequency (10⁴–10⁷ Hz) at various temperatures (300–400 K). The Nyquist plots are well fitted to an equivalent circuit consisting of a series of combination of grains and inhomogeneous electrode surface effect. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. Moreover, the near value of the activation energies obtained from the equivalent circuit and analysis of M″ confirms that the transport is through ion hopping mechanism dominated by the motion of the proton in the structure of the investigated material.     

Optical and structural characterization of iron oxide and cobalt oxide thin films at 800 nm

We report on optical and structural properties of α-Fe₂O₃ and Co₃O₄ thin films, grown by direct oxidation of pure metal films deposited on soda-lime glass. Structural characteristics and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Linear optical absorption, and linear refraction as well as nonlinear optical properties were investigated. The third-order optical susceptibilities were measured applying the Thermally managed Z-scan technique using a Ti: sapphire laser (150 fs; 800 nm). The results obtained for the Co₃O₄ film were \( \text{Re} \chi^{\left( 3 \right)} \) = ?(5.7 ± 2.4) ×10^?9 esu and \( \text{Im} \chi^{(3)} \) = ?(1.8 ± 0.2) ×10^?8 esu while for the α-Fe₂O₃ film we determined \( \text{Re} \chi^{(3)} \) = +(6.6 ± 2.4) ×10^?10 esu and \( \text{Im} \chi^{(3)} \) = +(2.2 ± 0.4) ×10^?10 esu.     

Electrical conductivity and dielectric relaxation behavior of AgFeP2O7 compound

In the present study, AgFeP₂O₇ was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. Not only were the impedance spectroscopy measurements of our compound carried out from 209 Hz to 5 MHz over the temperature range of 553 K–698 K but its AC conductivity as well as the dielectric relaxation were evaluated. Impedance measurements show AgFeP₂O₇ an ionic conductor being the conductivity 1.04?×?10^–?5(Ω^–?1cm^–?1) at 573 K. The conductivity and modulus formalisms provide nearly the same activation energies for electrical relaxation of mobile ions revealing that transport properties in this material appear to be due to an ionic hopping mechanism dominated by the motion of the Ag⁺ ions along tunnels presented in the structure of the investigated material.     

Structural,electrical, and transport number studies of AgI-doped silver borotellurite fast ion conducting glass system

Silver ion conducting glass system composed of xAgI–(100???x)[0.444 Ag₂SO₄–0.555 (0.4TeO₂–0.6B₂O₃)] has been prepared by melt quenching method for x?=?0 to 80 in step of 10. XRD, DSC, FTIR, and SEM were carried out to understand some structural properties of prepared samples. XRD and DSC studies of the samples with x?≤?60 show predominantly glassy nature. Electrical parameters and activation energies of all the samples were evaluated by complex impedance analysis and Arrhenius plots of DC conductivity, respectively. Carrier concentration, mobility, inter-ionic distance, and ionic conductivity of samples were measured and discussed. It is observed that the conductivity varies with increasing the temperature and composition. The highest conductivity (1.8?×?10^?1 S cm^?1) and ionic current (8.33 μA) is observed for =?50 sample at room temperature; hence, it can be used as best electrolyte material for solid-state battery application.     

Genesis,structural, and transport properties of La<Subscript>2</Subscript>Mo<Subscript>2-x</Subscript>W<Subscript>x</Subscript>O<Subscript>9</Subscript> prepared via mechanochemical activation

Fast oxide-ion conductors La₂Mo_2-xW_xO₉ (x = 0–1) have been prepared using mechanochemical activation (MA) of starting oxides in a high-power planetary ball mill. Studies of La₂Mo_2-xW_xO₉ genesis and structural properties using thermal analysis, XRD, SEM, IR, and Raman spectroscopy have revealed that MA results in the formation of an amorphous precursor, while the cubic β-phase is formed after calcination at 700–900 °C. Due to a high dispersion of powders, high-density pellets of W-LAMOX ceramics have been obtained already after sintering at 950 °C. Their electrical conductivity measured by the impedance spectroscopy depends on the W concentration being sufficiently high (up to 5.6?10^?3 S/cm at 630 °C) at temperatures below 650 °C.     

Electrical conduction and thermodynamic properties of K2NiP2O7

The pyrophosphate K₂NiP₂O₇ has been synthesized by the classic ceramic method and characterized by X-ray diffraction, solid-state ³¹P magic angle spinning (MAS) NMR, and IR and electrical impedance spectroscopy. The solid-state ³¹P MAS NMR, performed at 121.49 MHz, shows two isotropic resonances at ?17.66 and ?19.94 ppm, revealing the existence of two phosphorus environments in the structure. The electrical conductivity and dielectric properties have been investigated in the frequency and the temperature range of 200 Hz–1 MHz and 603–728 K, respectively. The frequency dependence of the conductivity is interpreted using the augmented Jonscher relation. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity imply that the transport is through ion hopping mechanism. The charge carrier concentration in the investigated sample has been evaluated using the Almond–West formalism and shown to be independent of temperature. Thermodynamic parameters such as the free energy of activation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated.     

Thermodynamic properties and application of CBH model in the ac conductivity of LiNi1.5P2O7 ceramic

The LiNi_1.5P₂O₇ compound was prepared by the solid-state reaction method at 923 K and characterized through XRD and Raman spectroscopy techniques. The impedance spectroscopy measurements were performed in the frequency and the temperature range (300 Hz–5 MHz) and (633–729 K), respectively. The ac conductivity for grain contribution is interpreted using the universal Jonscher’s power low. The exponent n decreases with increasing temperature which reveals that the conduction inside the studied material is insured by the correlated barrier hopping (CBH) model. The parameters of CBH model were determined showing that the ac conduction is realised by single-polaron hopping mechanism. Thermodynamic parameters such as the free energy for dipole relaxation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated.