Complex Impedance Spectra Research Articles

Anomalous electrical performance of A-site double-bivalent-doped Bi0.49Na0.5TiO3- ceramics from nominal oxygen deficiency to excess

Perovskite structural Bi 0.5 Na 0.5 TiO 3 (BNT) ferroelectrics can exhibit considerable ionic conductivity, giving a new area for the application as oxygen ion conductors. Through acceptor doping and A-site nonstoichiometry, an ionic conductive mechanism associated with well-resolved arcs in the complex impedance spectra is proposed. Different dielectric responses in ceramics can be deduced to probe the electrical inhomogeneities in separative regions, such as bulk, grain boundary, and electrode, regions. Generally, ionic conductivity only arises at the nominal oxygen deficiency composition of BNT based ceramics. Although large current leakage can exist in the BNT ferroelectrics, they overall display an insulative nature and dominate the electronic conductive contribution, and only a large main arc can be identified in the Nyquist plots. In this work, A-site bivalent doped Bi 0.49- x (SrBa) x Na 0.5 TiO 3- δ and Bi 0.49- x (SrCa) x Na 0.5 TiO 3- δ ceramics ranging from oxygen deficiency to excess are investigated. However, anomalous ionic conductive characteristics are achieved at nominal oxygen excess composition. Herein, the polarization and conductive mechanisms are discussed to elucidate the effect of compositions and their phase and microstructure on the AC impedance, dielectric, and ferroelectric performances. The inhomogeneous distribution of oxygen vacancies, resulting from element segregation or distorted phases in the respective electroactive domains, is a crucial issue in the design of BNT based dielectrics or ionic conductors.

The Effect of Surface Hydroxyls on the Humidity-Sensitive Properties of LiCl-Doped ZnSn(OH)6 Sphere-Based Sensors.

Pure zinc hydroxystannate (ZnSn(OH)6) and LiCl-doped ZnSn(OH)6 have been synthesized through a facile wet chemical method. The LiCl-doped samples keep their original spherical morphology as pure ZnSn(OH)6, with some LiCl particles stuck to its surface, providing more active sites for the adsorption and desorption of water molecules. The influence of LiCl doping on the humidity-sensing properties was explored by varying the dopant concentration. The 16 wt% LiCl/ZnSn(OH)6 showed a better humidity-sensing performance than that of the pure ZnSn(OH)6 and other doped samples, including a high resistive sensitivity, a relatively small hysteresis, and a fast response speed. Through the FTIR analysis, the number of hydroxyl groups on the surface structure after aging has been found to decline markedly. These hydroxyl groups provide a platform for the adsorption of water molecules on the surface and promote the dissociation of water molecules. The detriment of aging to sensor performance should not be underrated. The complex impedance spectrum explains the mechanism of the sensor. These results demonstrate that ZnSn(OH)6 has potential application in fabricating humidity sensors, and the sensing performance of the sensor is enhanced by the dopant LiCl.

Complex impedance and electrical conduction analysis of Ho2O3 doped CaCu3Ti4O12 NTC ceramics

ABSTRACT The structure and electrical properties of CaCu3Ti4O12 (CCTO) ceramics doped with xHo2O3 synthesized by solid-phase reaction method were systematically studied. Insights from X-ray diffraction (XRD) measurements indicate the existence of a primary phase of CCTO in all samples. Ho2O3 dopant was found to inhibit grain growth and thus leading to a reduced grain size of ceramics. Moreover, the distribution of resistivity with temperature revealed the manifestation of a negative temperature coefficient (NTC) effect in the samples. More specifically, the resistivity (ρ 20) values of obtained ceramics configurations decreased from 8.54 × 106 to 1.76 × 105 Ω cm with increasing Ho2O3 doping content. In addition, thermal constant (B 20/75) of all samples was higher than 4000 K. Electrical properties analysis disclosed that electron hopping process is main conduction mechanism within CCTO-based ceramics. In addition, insights from complex impedance spectra revealed the existence of grain boundaries with resistance higher than grains resistance. This effect is strongly connected with the manifestation of electrical relaxation procedures within grain boundaries. Our outcomes verify that both the structural configuration and the electrical performance of the CCTO-based ceramics can be tuned directly and effectively by incorporating Ho2O3 dopant.

Structural, dielectric, and impedance spectroscopy investigation of titanium dioxide electronic system

Titanium dioxide (TiO2) is one of the famous metal oxides, which is explored for many potential applications because of having distinctive characteristics. This article demonstrates the detailed structural and electrical properties of TiO2 material which is processed and synthesized by a high-temperature low-cost solid-state method. Dielectric parameters (dielectric constant: εr and tangent loss: tanδ), and complex impedance spectrum are inspected to evaluate the conductive, capacitive, and resistive performance of the material. The investigated material TiO2 has a large dielectric constant and low tangent loss, which makes it a potential contender for device applications at high temperatures. The imperative physiochemical properties allied with this sample may be very much useful in future electronic devices.

Dielectric and physical properties of aqueous solutions of 1,3-dimethylurea at 298.15 K

The complex dielectric function ε*(ω) = ε'(ω)-jε“(ω) is studied for aqueous solutions of 1,3-dimethylurea (1,3-DMU) at constant temperature 298.15 K across the frequency range 20 Hz to 2 MHz. Dielectric properties are measured using Agilent E 4980 precision LCR meter with a four terminal liquid test fixture (Agilent-16452). From measured dielectric data, the frequency dependent electric modulus M*(ω), electrical conductivity σ*(ω) and complex impedance spectra Z*(ω) were obtained. Effects of concentration variation of 1,3-DMU in distilled water on dielectric and electrical properties are discussed to gain information about the self-aggregative nature of 1,3-dimethylurea and dissociation process in aqueous solutions. Density, viscosity, and refractive index of all the solutions are measured and reported.

Synthesis, structural and electrical characterization of a new organic inorganic bromide: [(C3H7)4N]2CoBr4.

A new organic inorganic hybrid [TPA]2CoBr4, where TPA = [(C3H7)4N]+ (i.e., tetra-propyl-ammonium) compound has been synthesized by slow evaporation method at room temperature. Single crystal X-ray diffraction (SC-XRD), X-ray powder diffraction (XRPD), thermal analyses, vibrational and complex impedance spectroscopy have been used to characterize both structural, thermal, electrical properties. [TPA]2CoBr4 crystallizes in the monoclinic system (C2/c space group) with the following cell parameters: a = 33.145 (5) Å, b = 14.234 (3) Å, c = 15.081 (2) Å and β = 110.207 (5)°. In the crystal structure, the organic TPA cations which form layers stacked along the a-axis, are separated from each other by inorganic tetrahedral [CoBr4]2− anions. The XRPD pattern confirms both the high purity of the sample and the crystalline nature of the powder. The differential scanning calorimetry (DSC) analysis shows an endothermic peak at 394 K upon heating which is ascribed to a structural phase transition since no decomposition of the titled compound is evidenced by thermogravimetric analysis. The ac conductivity and the dielectric properties confirm the presence of the phase transition. At the structural phase transition around 394 K, a change from a quantum mechanical tunneling to a correlated barrier hopping conduction models is determined from the temperature dependence of the exponent s of the Jonscher's power law. The analysis of complex impedance spectra shows that the electrical properties of the material are heavily dependent on frequency and temperature, indicating a relaxation phenomenon and semiconductor-type behavior. One single semicircle is detectable in the Nyquist plots of the complex impedance spectra which can be satisfactorily fitted with a combination R//CPE elements assigned to the bulk response. This behavior suggests that the sample is electrically homogeneous. Capacitance analysis proves the high effective permittivity at radio frequencies in the sample.

Preparation and Research of a High-Performance ZnO/SnO2 Humidity Sensor

A high-performance zinc oxide/tin dioxide (ZnO/SnO2) humidity sensor was developed using a simple solvothermal method. The sensing mechanism of the ZnO/SnO2 humidity sensor was evaluated by analyzing its complex impedance spectra. The experimental results prove that the ZnO/SnO2 composite material has a larger specific surface area than pure SnO2, which allows the composite material surface to adsorb more water to enhance the response of the ZnO/SnO2 humidity sensor. ZnO can also contribute to the generation of oxygen-rich vacancies on the ZnO/SnO2 composite material surface, allowing it to adsorb a large amount of water and rapidly decompose water molecules into conductive ions to increase the response and recovery speed of the ZnO/SnO2 humidity sensor. These characteristics allowed the Z/S-2 humidity sensor to achieve a higher response (1,225,361%), better linearity, smaller hysteresis (6.6%), faster response and recovery speeds (35 and 8 s, respectively), and long-term stability at 11–95% relative humidity. The successful preparation of the ZnO/SnO2 composite material also provides a new direction for the design of SnO2-based resistance sensors with high humidity-sensing performance.

Ion-Conducting Flexible Thin Films of Composites from Poly(ethylene oxide) and Nematic Liquid Crystals E8-Characterization by Impedance and Dielectric Relaxation Spectroscopy.

Complex electrical impedance and dielectric spectroscopy were applied to study the dielectric relaxations and their thermal behavior in ion-conducting composites/complexes from polymer poly(ethylene oxide) (PEO) and E8 nematic liquid crystals (LCs), at the compositional ratio PEO:E8 = 70:30 wt%. Flexible thin films of PEO/E8 with a thickness of 150 μm were inspected, as well as such films from Na+ ion-conducting electrolyte PEO/E8/NaIO4 with the same PEO:E8 compositional ratio, but additionally containing 10 wt.% from the salt sodium metaperiodate (NaIO4) as a dopant of Na+ ions. The molecular dynamics, namely the dielectric relaxation of PEO/E8 and PEO/E8/NaIO4, were characterized through analyses of complex impedance and dielectric spectra measured in the frequency range of 1 Hz–1 MHz, under variation of temperature from below to above the glass-transition temperature of these composites. The relaxation and polarization of dipole formations in PEO/E8 and PEO/E8/NaIO4 were evidenced and compared in terms of both electrical impedance and dielectric response depending on temperature. The results obtained for molecular organization, molecular relaxation dynamics, and electric polarization in the studied ion-conducting polymer/LC composites/complexes can be helpful in the optimization of their structure and performance, and are attractive for applications in flexible organic electronics, energy storage devices, and mechatronics.

Vogel Fulcher analysis of electrical studies of NBT-CT ceramic composites

Impedance spectroscopy analyses of (1-x)Na0.5Bi0.5TiO3+(x) CaTiO3(NBT-CT) where x = 0.05, 0.10, 0.15, 0.20 are studied. The present samples reveal a non-Debye type relaxation phenomenon. The grain conduction effect is observed from complex impedance spectrum by the appearance of one semi-circular arc in Nyquist plot. Relaxation time of the samples is calculated by fitting Vogel-Fulcher law. DC conductivity is performed on samples and observed that resistance decreases with an increase in temperature showing a negative temperature coefficient of resistance (NTCR). The frequency-dependent AC conductivity at different temperatures indicates that conduction process is thermally activated. The activation energy has been calculated from Arrhenius plot of DC conductivity and relaxation frequency.

Electrical transport properties of V2O5-added Ni–Co–Zn ferrites

Frequency-dependent dielectric constant, dielectric loss, AC conductivity values and complex impedance spectra of V2O5-added Ni–Co–Zn ferrites ([Formula: see text][Formula: see text][Formula: see text]Fe2[Formula: see text] [Formula: see text]V2O5, where [Formula: see text] 0, 0.5, 1 and 1.5 wt.%) have been investigated at room temperature. The dielectric properties of the samples follow the Maxwell–Wagner polarization model. An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples. The dielectric constants decreased with the addition of V2O5, while the electrical resistivities of V2O5-added Ni–Co–Zn ferrites are found to be larger than that of pure Ni–Co–Zn ferrite. The AC conductivity was reduced with the addition of V2[Formula: see text]to Ni–Co–Zn ferrite at lower-frequency region. However, AC conductivity shows a sharp increase at higher-frequency region, which could be attributed to the enhancement of electron hopping between the Fe[Formula: see text] and Fe[Formula: see text] ions in the ferrite matrix due to the activity of the grains. The complex impedance spectroscopy results through Cole–Cole/Nyquist plot have demonstrated a single semicircular arc. It indicates that conduction mechanism takes place predominantly through the grain/bulk property, which could be ascribed to the larger grain size of V2O5-added Ni–Co–Zn ferrites.

Electronic tongue based on a single impedimetric sensor and complex numbers-supervised pattern recognition

This work investigated the application of supervised pattern recognition of complex number data obtained by electrochemical impedance spectroscopy (EIS) in order to obtain qualitative/discriminatory electroanalytical methods based on electronic tongues/noses. As a case study, electrochemical impedance spectra of aqueous extracts of coffee samples were obtained with a single label-free sensor and submitted to complex numbers-supervised pattern recognition to detect the adulteration of ground roasted coffee by the addition of coffee husks and sticks. Partial least-squares discriminant analysis (PLS-DA) and soft independent modeling by class analogy (SIMCA), two of the most employed multivariate classification techniques, were evaluated to classify coffee samples as adulterated or unadulterated by the direct analysis of complex impedance spectra. They are techniques whose mathematical logic can be easily employed in the treatment of complex numbers with very little or even no modification, by using the Hermitian transpose instead of the common nonconjugate transpose. The predictive ability of complex numbers–supervised pattern recognition on the identification of adulterated ground roasted coffees was compared to that obtained with impedance data presented as real numbers – real (Z’), imaginary (Z”), absolute impedance (|Z|), and phase angle (ϕ). A discussion about the most suitable classification algorithm for the type of data employed was held. The highest predictive ability was obtained by applying complex numbers-PLS-DA, with 100 % and 96 % of the adulterated and unadulterated test samples correctly identified, respectively, with no need for reducing complex spectra to real numbers.

Highly sensitive humidity sensor based on the solid solution Zr0.2Ti0.8O2 nanofibers

The ZrxTi1−xO2 (x = 0.0–0.5) nanofibers were synthesized by an electrospinning process. The influences of zirconium incorporation on the structure, phase composition, lattice parameters, morphology, specific surface area, and surface states were investigated in terms of XRD, SEM, BET, and XPS tests. The humidity sensing performances were also carried out in detail. It can be concluded that the replacement of Zr at Ti-site had significant impacts with regard to the phase structure: the anatase-rutile phase transformation was inhibited by Zr4+ ion doping; Zr4+ ion was successfully incorporated into the TiO2 lattice through a substitutional mode resulting in the formation of solid solution ZrxTi1−xO2 (x = 0.1–0.2) with anatase structure; when the Zr4+ ion was saturated, excessive Zr4+ ion formed new phase of Ti2ZrO6 and ZrTiO4 (nominal x ≥ 0.3); the lattice parameters and the cell volume increased as Zr4+ ion incorporation. The solid solution Zr0.2Ti0.8O2 nanofibers had the highest Ti3+ abundance among the samples with x ≤ 0.2, accompanied by the highest oxygen vacancies. Moreover, the solid solution Zr0.2Ti0.8O2 nanofibers exhibited the best humidity sensing properties: excellent sensitivity as proven by four orders of magnitude change to impedance at 11–95% relative humidity (RH), negligible hysteresis, rapid response and recovery speed as well as superior stability, which were induced by high concentration of oxygen vacancies combined with reactive Ti3+ ions. A detailed study of the sensing mechanism was also performed in terms of complex impedance spectra.

Humidity Sensing Properties and Negative Differential Resistance Effects of TiO2 Nanowires

This paper reports a humidity sensor based on TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowires. The humidity sensor prepared with a simple and easy technology exhibits obviously high sensitivity and fast response/recovery speed. A series of analyses including scanning electron microscopy, specific surface area analysis, water contact angle, and complex impedance spectrum were used to analyze superior humidity sensing performance of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowires. The results demonstrate that higher sensitivity of the sensor probably stems from larger specific area of nanowires, and its faster response might be attributed to the continuity of nanowires and their intricate connection network, which offer highways for water molecules diffusion and charges transport. Besides, the current-voltage characteristic of the sensor presents a negative differential resistance effect (NDR) with a very low bias voltage under certain humidity level at room temperature, which facilitates compatibility with some low voltage integrated circuit. The tip enhancement of electric field caused by TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowire end is suggested to explain the mechanism of NDR at very low bias voltage. The high-performance humidity sensor provides a way to study the gender difference in moisture loss through skin evaporation with a non-contact manner, which can avoid the interference of contact state between the sensor and the skin.

Electrical properties of La-Mn-codoped BaTiO3-(Bi0.5Na0.5)TiO3 lead-free PTCR ceramics

La-Mn-codoped 0.97BaTiO3-0.03(Bi0.5Na0.5)TiO3 ceramics (abbreviated as xLa-yMn-BBNT3, x = 0.001, 0.002, 0.003, 0.004; y = 0, 0.0005, 0.001, 0.0015, 0.002) for application of lead-free positive temperature coefficient of resistivity (PTCR) thermistors were prepared using a wet chemical route. The analysis of XRD patterns shows that all prepared powders and ceramics are composed of pure tetragonal perovskite phase. The x = 0.002 La-doped ceramic sintered in air has a Curie temperature of Tc about 140 °C, room-temperature resistivity (ρ25) of ~103 Ω cm and resistivity jump (log(ρmax/ρmin)) of ~3 orders in magnitude. It is also found that the resistivity jump of prepared ceramic reaches up to 4.4 orders in magnitude when y = 0.0015 Mn was doped. Influence of grain and grain-boundary effect on PTCR effect was analyzed by complex impedance spectra measured at different temperatures, and the results reveal that the grain boundary effect plays key role in the PTCR effect.

Effect of annealing temperature on dielectric properties of iron oxide prepared by sol–gel auto combustion method

In this study, different phases of iron oxide have been synthesized by sol–gel auto combustion route followed by annealing. Temperature and frequency-dependent dielectric properties have been studied in detail which provide the information on the contribution of grain and grain boundary in charge transport. Conductivity and electric modulus spectra have also been analyzed. The scaled coordination of impedance spectrum merges in a single master curve which signifies that the distribution of relaxation time is temperature independent. Complex impedance spectra have been used to evaluate activation energy (Ea ) by using Arrhenius relation. The activation energy calculated for α-Fe2O3 is 1.36 eV.

Development of a rGO-BiVO4 Heterojunction Humidity Sensor with Boosted Performance.

Humidity sensors with good repeatability, low hysteresis, and low-power consumption are increasingly important for environmental monitoring and industrial control applications. Herein, an impedance-type humidity sensor under low working voltage (5 mV) utilizing a rGO-BiVO4 nanocomposite is demonstrated. The rGO-BiVO4 humidity sensor exhibits superior sensing performances, including good repeatability, negligible hysteresis (0.47%), fast response and recovery time, low power consumption, good stability, and anti-interference ability. The ultraviolet-visible absorption spectrum reveals that the narrow band gap of the rGO-BiVO4 nanocomposite is conductive to the electron transfer. The complex impedance spectra and the energy band structure analysis further suggest that the boosted humidity performance results from the formation of a heterojunction and the decrease of the heterojunction barrier height. The facile fabrication route, enhanced sensing performance, and excellent device reliability make the rGO-BiVO4 sensor highly attractive for high-end humidity sensing applications.

Colossal dielectric response, multiferroic properties, and gas sensing characteristics of the rare earth orthoferrite LaFeO3 ceramics

A great impact of the multifunctional or multiferroic materials on device applications has gained tremendous attention from scientific research groups in the field of materials science. The multiferroic materials bear superior properties of alternating the ferroic orders in a pre-designed way to match the device specifications. Materials in which there is a coupling between the primary ferroic orders (ferroelectric, ferromagnetic, ferroelastic) are termed multiferroics. This paper shows the investigation of a room temperature multiferroic material bearing a chemical composition LaFeO3 (LFO) also known as rare-earth orthoferrites. The particles of LFO are synthesized employing mixed oxide processing with heat treatment. The Rietveld analysis of the material shows that the LFO crystallizes having an orthorhombic symmetry and Pbnm space group. The complex impedance spectra indicate the distribution of relaxation time and non-Debye-type behavior. The dielectric parameters measured at various frequencies and temperatures suggest the formation of a colossal dielectric constant and low loss. The elemental analyses of the material show that there is no impurity present in the material. The pellet of the LFO arranged in a metal-insulator-metal arrangement is tested for gas sensing application. The LFO material has an excellent selectivity towards NO2 gas at relatively low operating temperatures ranging from 50 °C to 300 °C along with a sub-ppm limit of detection. A set of cyclic testing confirms that LFO can carry out stable and lengthy gas sensing operations while demonstrating outstanding adsorption and desorption characteristics. Such superior gas sensing properties and dielectric characteristics can pave the way toward the ultra-high sensitive gas sensors based on lead-free orthoferrites perovskites.

Enhanced sensitivity of humidity sensor using Nafion/graphene oxide quantum dot nanocomposite

In this paper, a capacitance humidity sensor which was fabricated by interdigital electrodes (IDEs) coated with Nafion/graphene oxide quantum dot (GOQD) thin film was reported. The sensor could convert concentration change of moisture into capacitance change of the IDEs. The morphological and nanostructure of the prepared Nafion/GOQD nanocomposite were characterized by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), confirming that the Nafion/GOQD nanocomposite was successfully prepared. Test result showed that the proposed sensor exhibited higher sensitivity of 1025.99 pF/%RH (nearly double) and better linearity, compared with pure Nafion sensor, which could be ascribed to formation of a subordinate-assembly of 0D GOQD in the Nafion film. Furthermore, the humidity sensor exhibited excellent repeatability, fast response and recovery, and little hysteresis. It could offer a potential method to monitor the respiration. Lastly, the humidity sensing mechanism was studied through complex impedance spectra (CIS).

Structural and stability analysis of Na4Mn4Ti5O18 for energy storage application

We report a single-phase Na4Mn4Ti5O18 oxide prepared via ceramic processing route. Rietveld refinement of X-ray diffraction results indicated orthorhombic unit cell indexed with Pbam space group. Further, structural analysis using X-ray diffraction, transmission electron microscopy and Raman spectroscopy suggested crystal structure comprising two distinct tunnel pathway, polygonal and Z-shaped tunnels with void dimensions ~ 4.07 A and ~ 3.01 A, respectively, suitable for reversible cation transport desirable for energy storage applications. X-ray photoelectron spectroscopy confirmed presence of Mn2+, Mn3+, Mn4+ and Ti4+ in Na4Mn4Ti5O18. Surface morphology in field emission scanning electron microscopy exhibited inhomogenously distributed micro-bead grains separated by well-defined boundaries in good agreement with complex impedance spectrum results. Estimated dc conductivity and surface area is ~ 1.745 × 10− 6 S cm− 1 and ~ 0.66 m2g− 1 respectively. Electrochemical energy storage performance with cell; Na || 1 M NaFSI (EC : DMC, 1:1 v/v%) || Na4Mn4Ti5O18 in voltage range 2.0–3.8 V indicated reversible redox action. Identical cell in voltage range 0.01–2.5 V, exhibited pseudo-capacitive behaviour. Results suggest energy storage possibility with Na4Mn4Ti5O18 electrode.

Broadband dielectric spectroscopic investigation of Melaminium bis (trichloroacetate) dihydrate—a nonlinear optical single crystal

In this report, a detailed study on dielectric and charge transport properties of the nonlinear optical material—melaminium bis (trichloroacetate) dihydrate (MTCA) is given. It is evident that there is no ferroelectric or antiferroelectric polarization in the material. It is expected to have a piezo-electric property, not a ferroelectric as the material is a non-centrosymmetric crystal. The dielectric characteristics of the specimen was carried out in a range of frequencies between 50 Hz and 5 MHz at different temperatures viz 313 K, 333 K, 353 K and 373 K. It is observed that slow down occurs at low temperatures and the hopping mechanism takes place based on localized charge carriers. The results of a complex impedance spectrum indicate that single relaxation processes occur at high frequencies. A detailed report on temperature and frequency dependence of materials’ properties of MTCA is provided in this communication.