AC Conduction Mechanism Research Articles

Influence of Sb doping on thermal properties and electrical conductivity mechanism of SbxSe50–xSn20Te30 chalcogenide glassy systems

Tunability of thermal, and electrical characteristics of SbxSe50-xSn20Te30 (x = 2, 4, 6, and 8 at. %) bulk glass systems with varying doping concentrations are the major objective of this study. The melt quenching technique has been employed to synthesize the samples. Various thermal parameters have been inspected by using DSC measurements. The effect of Sb addition on the glass transition temperature (Tg), crystallization temperature (Tc), peak crystallization temperature (Tp), and melting temperature (Tm) have been observed from DSC thermograms. The dependence of Tg, Tc, Tp, and Tm on the heating rate has been measured. The thermal analysis is performed under non-isothermal conditions at heating rates of 5, 10, 15, and 20 K/min. The activation energies for the glass transition temperature are estimated by using the Kissinger method and are found to decrease from (211.21-168.85) KJ.mol−1. Thermal stability and glass forming ability for all glassy compositions have been examined in terms of Hruby's parameter. In addition, electrical conductivity mechanisms over vast temperature and frequency ranges are analyzed. The DC conductivity mechanism has been analyzed by deploying Mott and Greaves's variable range hopping model, while the AC conductivity mechanism has been analyzed by deploying the modified correlated barrier hopping model. AC conductivity scaling property has been examined by using the Pan and Ghosh model. The influence of Sb addition has been observed as the DC and AC conductivity increases with the increase of doping concentration.

Electrical conductivity and hopping conduction mechanism by VRH model in halide modified tellurite glasses

Electrical properties of halide doped tellurium glasses with composition 60TeO2-(25-x) Bi2O3-15B2O3-x ZnCl2, where x varies from 0 to 20 with step-size 5 has been studied in frequency range 10-1 Hz–105 Hz and temperature range of 200°C–300°C. The frequency-dependent conductivity was found to obey Almond-West's universal powers law and parameters such as frequency exponent (s), DC conductivity, and crossover frequency were obtained by fitting the ac conductivity experimental data with Almond-West's universal powers law. Based on estimated s values the electrical conduction model was depicted, and it was found that the correlated barrier hopping (CBH) model provides a pretty realistic depiction of the primary AC conduction mechanism. Further, the migratory enthalpy (Hm) and the enthalpy required to remove the cation from its initial position near a charge-compensating centre (Hf) were calculated. Further, Variable range hopping, or VRH, was found to be the process by which charges move between localized states.The electric modulus (M″) fitting with the Kohlrausch-Williams-Watts (KWW) function revealed non-Debye-type relaxation in the examined glass samples. Activation energy estimated from conductivity (1.13–1.20 eV), and electric modulus (1.13–1.22 eV) analysis are in good agreement indicating that polarons had to overcome a constant energy barrier throughout both the relaxation and conduction phases. One master curve was produced for all compositions and temperatures as a result of an impressive convergence in the scaling spectra of the AC conductivity and electric modulus (M′ and M″). Therefore, it was concluded that neither temperature nor composition impacted the conduction or relaxation mechanisms seen in the glass samples under study. The dielectric properties studies suggested non-debye type behavior.

Silicon nitride resistance switching MIS cells doped with silicon atoms

Stoichiometric SiNx layers (x = [N]/[Si] = 1.33) are doped with Si atoms by ultra-low energy ion implantation (ULE-II) and subsequently annealed at different temperatures in inert ambient conditions. Detailed material and memory cells characterization is performed to investigate the effect of Si dopants on the switching properties and performance of the fabricated resistive memory cells. In this context extensive dc current–voltage and impedance spectroscopy measurements are carried out systematically and the role of doping in dielectric properties of the nitride films is enlightened. The dc and ac conduction mechanisms are investigated in a comprehensive way. Room temperature retention characteristics of resistive states are also presented.

Effect of Zn doping on optical properties and electrical conductivity-mechanism of Sb-Ge-Se chalcogenide glassy systems

The present communication inspects the impact of zinc doping on the s optical, and electrical characteristics of bulk glassy samples made up of xZn-(0.1-x)Sb-0.2Ge-0.7Se (x = 0.01, 0.02, 0.03, 0.05). The X-ray diffraction patterns confirm that the samples are amorphous. In addition to various optical constants, the linear refractive index, and skin depth have been determined. The decreases in band gap energy values from 1.62 eV to 1.56 eV may be attributed to the rise in Unbach energy values from 0.15 eV to 0.32 eV. The obtained value of refractive indices also increases from 2.91 to 2.95 with the rising Zn content. By using the paradigm of Jonscher's universal power law and the Almond-West formalism, the underlying mechanisms of AC conductivity have been investigated. The AC conductivity increases with temperature and displays semiconducting characteristics. As the power-law exponent (s) reduces with increasing temperature, the correlated barrier hopping model is used to explain the AC conduction mechanism. DC conduction mechanism is described by Mott's and Greaves's variable range hopping model. The anticipated values of tiny polaron hopping energy (Whop) and hopping distance (Rhop) shed light on the increasing trend of DC conductivity with increased Zn concentration.

Effect of the inclusion of Fe2O3 on the optical and electrical transport properties into sodium-zinc-phosphate quaternary glassy systems

Glass systems, xFe2O3–(35-x)Na2O–25ZnO–40P2O5) (x = 10, 15, 20, and 25 mol%), were prepared using the melt-quenching technique. FTIR analysis revealed stretching vibrations of the P–O–P and P–O bonds and XRD investigation revealed a pure amorphous structure. It was discovered that with rising Fe2O3 content (x), the values of density increased, but the values of molar volume decreased. The Fe2O3 incorporation into the glass matrix resulted in decrement in the optical band gap energy (Eopt) value from 2.99 to 2.16 eV. The addition of Fe2O3 to the glass network reduced the quantity of non-bridging oxygen ions, improving the observed refractive index value. According to the Mott and Greaves model, the small polaron hopping model was responsible for the DC conductivity mechanism, and the density of states at the Fermi level increased as DC conductivity increased with increasing Fe2O3 content, but hopping distance (Rhop) and hopping energy (Whop) sharply decreased. It was concluded that the AC conductivity mechanism followed the correlated barrier hopping model as the power-law exponent (s) of Jonscher's universal power law decreased with temperature. AC conductivity increased with rising Fe2O3 concentration due to a decrement in the polaron hopping distance value and an increment in the concentration of defect pair states.

AC Conduction Mechanism and Impedance Analysis of Conventional and Plasma‐Sintered Yttria‐Stabilized ZrO2@Mullite Composite

AbstractThe addition of 8 mol% of Y2O3 to the ZrO2@mullite composites stabilizes the metastable tetragonal phase of ZrO2 in conventional and plasma‐sintered Y2O3‐stabilized ZrO2@mullite composites. A fused, highly dense, and interconnected microstructure is formed in the case of plasma‐sintered Y2O3 stabilized ZrO2@mullite composite. At 1 MHz frequency, the room temperature and tanδ of (10.37 and 2.06) is obtained for the conventional Y2O3 stabilized ZrO2@mullite composite and that of (38.8 and 4.02) is observed for the plasma sintered Y2O3 stabilized ZrO2@mullite composite. The substitution of Y3+ in place of Zr4+ creates sufficiently large oxygen vacancies at the grain boundary regions of these composites endowed mostly with the ZrO2 phase. In conventional Y2O3‐ ZrO2@mullite composites, both dielectric relaxation as well as conductivity relaxation are observed due to the dynamic motion of dipoles and relaxation due to the presence of defect states and porous structures. This leads to higher grain boundary conductivity than the grain conductivity of these composites. Thermally activated conduction mechanisms exhibited in these composite materials are projected from the complex impedance and modulus analysis. The conventional and plasma sintered Y2O3‐ ZrO2@mullite composite has an optical bandgap of 3.26 and 3.58 eV, respectively.

AC conductivity mechanism and dielectric relaxation of bulk Titanium phthalocyanine chloride (TiPcCl2)

AC conductivity mechanism and dielectric relaxation of bulk Titanium phthalocyanine chloride (TiPcCl2)

Temperature and frequency dependent dielectric capacitance and polarization performances of low dimensional perovskite based manganese stannate

Manganese stannate perovskite nanoparticles were synthesized by applying a complexation mediated approach. Rietveld refinement of the XRD data exhibited orthorhombic structure with space group of Pnma. The structure included eightfold coordinated Mn2+ cation, surrounded by eight O2− anions and formed MnO8 polyhedra unit. Each polyhedra unit interconnected through the corner-sharing SnO6 octahedra with the formation of a cage-like network. The temperature and frequency dependent dielectric performances of manganese stannate were measured in the form of a device, which exhibited maximum dielectric constant value ~ 3445. The high dielectric constant value was originated due to the contribution of space charge polarization and orientation polarization of dipoles within the measured frequency ranges. Temperature and frequency dependent AC-conduction mechanism of the manganese stannate-based device involved both overlapping large polarons and non-overlapping small polarons. Electric field-dependent of polarization hysteresis loop of the device exhibited the maximum polarization value 1.5 µC/cm2 under the electric field of 3 kV/mm. Under the applied field of 2 kV/mm, the device exhibited a fatigue-free polarization with a maximum value of 0.92 µC/cm2, sustained for 103 cycles under ambient temperature condition.

Negative permittivity at kHz regulated by length-diameter ratio of short carbon fibers in phenolic resin composites

Negative dielectric materials show bright application prospects in the electromagnetic protection, energy storage and radio transmission fields. However, high negative permittivity and expensive manufacturing costs limit their applications in above fields. Here, phenolic resin composites containing short carbon fibers (SCF) with different length-diameter ratios were prepared by mechanical mixing and dry pressing. The effects of length-diameter ratio and mass fraction of SCF on conductivity, permittivity and impedance were investigated. The AC conduction mechanism changed from jump conduction to metal-like conduction due to the increased carrier concentration resulting from improved connectivity of the 3D conductive network. In addition, a weak negative permittivity was obtained in SCF429-10/PF composite. At SCF of 20 wt%, when the length-diameter ratio increased from 114 to 429, the negative permittivity mechanism changed from Lorentz & Drude to Drude model, indicating that the plasma oscillation of delocalized electrons was the main cause of negative permittivity. The relationship between reactance and permittivity were discussed by impedance and equivalent circuit analysis. This work provided a new strategy for obtaining weak negative permittivity, which exhibited potential applications in the fields of electromagnetic protection, high dielectric capacitors, and perfect absorption.

Study of dielectric, impedance and transport properties of co-doped Ba0.5Sr0.5TiO3 ceramics

Dielectric properties and Electrical response of BST ceramics having composition Ba0.5Sr0.5Ti0.98Sn0.01Zr0.01O3 synthesized by solid state reaction route are studied in this piece of work. The structural part analysis is done using XRD technique and scanning electron microscopy and is confirmed to be of cubic structure. Electrical characterization through impedance and modulus spectroscopy is made over a frequency region of 1 kHz to 1 MHz from ambient temperature to 400 °C. Near constant value of Ɛr and significantly low and flat loss tangent at room temperature are achieved in the material which suggest possible application in electronic circuits. Temperature dependent broadened loss peaks observed beyond 250 °C indicated thermally activated conductivity/ relaxation process in the material. Impedance spectroscopy results were examined in alternate formalism for the role of grain boundary and grain in various processes. The computed activation energy for charge carriers provides information of the transport phenomena. The estimated values suggest that oxygen vacancies play important role in conduction process. The activation energy is estimated by fitting temperature dependent relaxation time with Arrhenius equation and the type of charge carriers involved in the relaxation process are suggested. Frequency dependent ac conductivity plots at various temperatures obey Johnscher’s law. Variation of exponent in Johnsher’s power law with temperature well agrees with correlated barrier hopping (CBH) model for ac conduction mechanism.

Mixed ionic and electronic conductivity in the quaternary V2O5–Na2O–ZnO–P2O5 glass system

The melt quenching method was adopted to synthesize glasses with the formula xV2O5–(0.4-x) Na2O–0.35ZnO–0.25P2O5 (x = 0.05, 0.1, 0.15, 0.2, and 0.25). X-ray diffraction patterns for the x = 0.05 sample showed the complete amorphous structure, whereas other composites revealed the development of nanocrystallites over the amorphous glassy networks. DSC measurement showed that glass transition temperature reduced as V2O5 concentration rose, and values were consistent with modified CBH model theoretical (fitting) data. DC conductivity for x = 0.05 and 0.1 composites followed an Arrhenius-type relation and linearity against the reciprocal of temperature, revealing ionic conductivity. On the contrary, the electronic or small polaron hopping mechanism was responsible for DC conductivity for all other composites. AC conductivity mechanism was described by the modified correlated barrier hopping model, and ideal glass transition temperatures were predicted (361 °C (x = 0.05) to 412 °C (x = 0.25)). It was observed that with rising V2O5 content (x), there was blockage of ionic pathways of Na+ ions, causing the ionic conductivity to decline and the electronic or small polaronic conductivity to enhance, as the radius of small polaron reduces. AC conductivity scaling property established that the time-temperature superposition principle and the BNN relation did not hold for the systems.

Physical properties and dielectric response of (Gd, Pr)-dual doped samarium iron garnet

Samarium iron garnet, Sm3Fe5O12, co-doped with Gd3+ and Pr3+ ions, having the chemical formula Sm3-2xGdxPrxFe5O12 (0.0 ≤ x ≤ 0.8), were synthesized by the co-precipitation method. The structural study confirmed the cubic crystallization of the Sm3Fe5O12 phase in the addition of two secondary phases, α-Fe2O3 and SmFeO3. The variation of the lattice parameters and crystalline size indicated that both Gd3+ and Pr3+ ions were incorporated into the lattice. The elemental analysis confirmed the stoichiometry proposed for Sm3-2xGdxPrxFe5O12. The co-doping process of SmIG affected the absorbance of photo-radiations, making them possible candidates for transparent electrodes and optoelectronic devices. Energy band gap values were in the range of 2.921–3.004eV. DC electrical conductivity measurements studied the transport properties through which two activation energies were determined. The co-doping process affected the dielectric constants (ε′, ε″, tan δ), which reached a maximum value for x = 0.2. Dielectric relaxation was observed in the measurements, which could be due to the presence of oxygen vacancies as detected in XPS results. The Nyquist plots revealed that all the samples exhibited a negative temperature coefficient of impedance, where the arc of the semicircles decreased as the temperature increased from 413 to 743K. Also, the contribution of the resistance at high-frequency was related to the grains and grain boundaries. The ac conductivity mechanism followed the small polaron and the correlated barrier hopping models. In the temperature range between 333 and 583K, the prepared samples are promising for ion-conducting glasses and ionic crystals.

Temperature Dependence of AC Electrical Conduction in Plasma Polymerized Pyrrole-N,N,3,5 Tetramethylaniline Bilayer Composite Thin Films

The temperature dependence of alternating current (ac) electrical conduction in Plasma Polymerized Pyrrole-N,N,3,5 tetramethylaniline (PPPy-PPTMA) bilayer composite thin films have been discussed in this article. The thin films were deposited by using a parallel plate capacitively coupled glow discharge reactor. To study the temperature dependence of ac electrical conduction the variation of dielectric constant (<i>ε</i>′), the dielectric loss factor (<i>ε</i>"), and the ac conductivity (<i>σ_ac</i>) of the thin films were investigated in the frequency range 100 Hz to 10 MHz and in the temperature range 298K to 398K. The decrease of dielectric constant <i>ε</i>′ with increasing frequency was observed and was attributed to the dielectric relaxation process. The dielectric constant, however, is observed to be increased with temperature in all frequency regions which is due to greater freedom of movement of dipole molecular chain in polymer films at high temperature. The variation of dielectric loss factor <i>ε</i>" with frequency showed a loss minimum then rises to a sharp peak which was also attributed to the relaxation phenomena of polymer. It is, however, observed that the loss peaks have shifted towards the higher frequency side with the increase of temperature which is usually attributed to dipolar orientation. The dielectric loss factor is also observed to be increased with temperature in all frequency regions. At lower frequencies the increase of loss factor with temperature was attributed to the effective chain motion of polymer and at high frequencies this increase might indicate the orientational polarization due to chain motion in bilayer film. The linear behavior of the ac conductivity <i>σ_ac</i> with the frequency and the observed weak temperature dependence of <i>σ_ac</i> led to interpret the ac conduction mechanism as the hopping between localized states at the Fermi level.

Synthesis, structural, optical and electrical characterization of Y2O3/poly(ethylene glycol)–poly(vinyl chloride) based nanocomposite solid polymer electrolytes

AbstractNanocomposite solid polymer electrolytes (NCSPEs) have attracted a lot of attention as excellent candidates for future electronics, photonics and energy storage devices. In this work, Y2O3 (YO) nanosheets were prepared by a free‐template sol–gel method and incorporated inside a poly(ethylene glycol)–poly(vinyl chloride) (blend) matrix via solution casting. NCSPE films were then prepared by adding NaClO4 (NC) or LiCl (LC) to the nanocomposite solutions. XRD and field emission SEM showed that YO has a body‐centered cubic structure and a crystallite size of 24.8 nm, and looks like nanosheets with a high purity. The XRD results of the films showed that YO loading and salt complexation increase the films' amorphous structure. SEM was used to study the surface morphology and film thickness. Fourier transform infrared spectra confirmed the complexation and interactions between the YO/blend and NC or LC. UV–visible spectroscopy revealed that the films display low transmittance (˂17%), an extinction coefficient k between 0.2 × 10−3 and 1 × 10−3 and a comparatively high refractive index. The band gap of the blend decreased from 4.3 to 4.0 eV on loading YO, and NC exhibited a higher impact on Eg compared with LC. A significant increase in with complexing was reported and the maximum value was 7.4 × 10−4 S cm−1 for the 10 wt% NC/YO/blend structure. The NCSPE films are ionic conductors and have a non‐Debye type of conductivity relaxation, and the applied AC conduction mechanism is correlated barrier hopping. © 2022 Society of Industrial Chemistry.

Effect of Alkaline earth oxides on the ionic conductivity of Boro-Tellurite glasses for solid state ion batteries

The complex impedance spectroscopy studies (electrical impedance, a.c. conductivity, dielectric constant, loss tangent) of the boro-tellurite glasses were measured as a function of the alkaline earth oxide content at broad range of frequencies and temperatures. Three series of boro-tellurite glasses containing BaO/SrO viz. BaO-TeO2-TiO2-B2O3 (BTTB), BaO-TeO2-B2O3 (BTB) and SrO-TeO2-TiO2-B2O3 (STTB) were prepared by the melt quenching method. The prepared glasses were characterized by XRD, DSC, density, FTIR and complex impedance spectroscopy experimental techniques. The XRD spectra exhibited no characteristic sharp peaks indicating the amorphous nature of the prepared glass samples. The glass transition temperature (Tg) values were evaluated from the DSC thermograms. The density values were found to increase with BaO content while they decreased with SrO content. This variation was attributed to the different density values of BaO and SrO. FTIR spectra revelated the presence of different structural units like BO3 and BO4. Impedance studies demonstrated that the replacement of TeO2 by the BaO content enhanced the ionic conductivity. The impedance plots of BTTB, BTB and STTB glasses exhibited nearlys semicircles. The bulk resistance (Rb) was calculated from the impedance plots. It was observed that the Rb values decrease with increasing BaO in BTTB and BTB glasses, while it increased with SrO in STTB glasses which may be attributed to the variation of mobile charge carriers. The Rb values vary as BTB > BTTB > STTB. The capacitance calculated from the impedance plots increased with increasing BaO mol% and decreasing SrO mol%. The capacitance also increased with increasing temperature. The power law exponent (k) values decrease with increasing temperature. Therefore, the ac conduction mechanism may follow correlated barrier hopping model. The real part of dielectric constant has high values at low frequencies, which decreased rapidly with surge of frequency. At high frequencies the contribution of charge accumulation is minimum resulting in constant

Electrical conductivity and relaxation phenomena in Li2O·B2O3 based glass and glass-ceramic: A comprehensive and comparative analysis

This work reports a detailed investigation on the electrical conductivity and dielectric relaxation phenomena in Li2O·B2O3 based glass and glass-ceramic materials. Measurements reveal that the electrical conductivity of glass-ceramic is lower than glass. This owes to occurrence of grain boundaries which impede the mobility of charge carriers in glass-ceramic as confirmed by FESEM micrographs. The frequency-dependent behavior of electrical conductivity, within the measured temperature range, is analysed using Jonscher's power law. It is found that the conductivity rises with an increase in temperature and the range of conductivity reveals the semiconducting behavior of the material. The ac conductivity mechanism of system is observed to follow the overlapping large polaron tunneling model. The conduction and relaxation mechanism studies are performed using electric modulus and impedance spectroscopy within the frequency and temperature ranges varied from 103 Hz to 107 Hz and 593 K–773 K, respectively. Analysis of the relaxation mechanism in both samples is performed employing Kohlrausch-William-Watts (KWW) model, which reveals that the charge carriers are following non-Debye type relaxation. To distinguish between the contribution of grain boundaries and grains in the relaxation mechanism, a combined analysis of complex electric module and impedance spectroscopy has been discussed.

Epsilon-near-zero response derived from collective oscillation in the metacomposites with ultralow plasma frequency

Nowadays, negative parameters have been originally brought up and investigated in the electromagnetic metamaterial, where the epsilon-near-zero (ENZ) response was dominated by collective plasma frequencies and carrier concentration. However, the ENZ response is missing at the radio frequency, leading to limitations on novel antennas and printed circuit board. Therefore, ternary copper/silica coated copper/polyvinylidene fluoride (Cu/Cu@SiO2/PVDF) composites were prepared to investigate the ENZ response at the radio frequency. With increasing the content of Cu granules, a transition from positive to negative permittivity was observed in the binary Cu/PVDF composites, in which negative permittivity was related to an inductive character. On the contrary, the binary Cu@SiO2/PVDF composites without any uncoated Cu granules exhibit positive permittivity, showing a capacitive character. In fact, negative permittivity was derived from the collective plasma oscillation of percolative Cu networks, and Cu@SiO2 granules were responsible for diluting effective electron concentration of Cu. For the ternary Cu/Cu@SiO2/PVDF composites, values of negative permittivity were suppressed to several orders of magnitude to −178 (measured at 1 MHz) and plasma frequency decreased to radio frequency about 106 rad/s. Besides, with the construction of percolative Cu networks, the Ac conduction mechanism was transformed from hopping conduction to metal-like conduction. Based on the equivalent circuit analysis, it showed that a permittivity transition was responsible for the capacitive to inductive character.

The role of bias voltage in charge carrier transport mechanism of organic semiconductor

The energy density of flexible electronics can be improved by storing charge at high voltage through the charge carrier transport in the organic semiconductor. However, voltage fluctuation triggers irreversible carrier recombination and associated heat generation, which influence interfacial and dipolar polarisation and a variation of relaxation phenomenon by densification of the space charge carriers in the electronic materials. This study provides a fundamental understanding of voltage variation and corresponding thermal variation via electrical transport properties measurement of 0.1 wt% and 0.5 wt% of cobalt oxide (Co3O4) on PVA flexible mat (Designated as PC0.1 and PC0.5 films). Here, we consider various models from the literature to demonstrate the effect of bias voltage on the transport properties of the flexible metal oxide film. The ac conduction mechanism follows a sharp transition of the Jonhcher power law to the jump relaxation model (JRM) around the system's glass transition temperature (Tg). The effect of the glass transition temperature is extensive analysis through the temperature-dependent real part of the dielectric and resistivity study. After Tg electrical transport properties of these composite films modifies significantly, as the resistivity follows Bӓssler's Gaussian disorder model (298–343 K) and Arrhenius model (348–383 K) in two different temperature regions. Further, we highlight the current-voltage characteristic at different temperatures and observe three different conduction mechanisms as trap free limited conduction (TFL) (−5 V→−1 V), Ohmic (0 V→+1 V), and Poole-Frenkel (PF) (1 V→+5 V) during trapping and de-trapping of the carriers in trap states. This fundamental study identifies the bias voltage effect in long-cycling organic electronics and enables us to market the implementation of flexible electronics with high-performance efficiency.

Enhanced electrical properties and conduction mechanism of A-site rare-earth Nd-substituted CaBi2Nb2O9

Calcium bismuth niobate (CaBi2Nb2O9, CBN) is considered to be one of the most promising high-temperature (HT) piezoelectric materials owing to its high Curie temperature of ∼940 °C, however, its low electrical resistance and poor piezoelectric properties at elevated temperatures limit its applications at high temperatures. In this work, we report the significantly enhanced dc electrical resistivity and piezoelectric performance of CBN ceramics through rare-earth Nd-substitution. The crystal structure, microstructure, and dielectric, electrical, ferroelectric and piezoelectric properties of Nd-modified CBN with nominal compositions of Ca1−x Nd x Bi2Nb2O9 (CBN-100xNd) have been investigated in detail. The results indicate that the substitutions of Nd3+ ions for Ca2+ ions increase the piezoelectric properties, and reduce the dielectric loss tanδ at high temperatures. The dc and ac conduction mechanisms indicate that the conduction mechanism is closely related to oxygen vacancies that are reduced through the donor substitutions of Nd3+ for Ca2+, thereby resulting in a significant improvement in the dc electrical resistivity. The optimal composition of CBN-3Nd exhibits a high piezoelectric constant d 33 of 13.5 pC N−1, and a high Curie temperature T c of 948 °C. More importantly, the CBN-3Nd exhibits good thermal stability of the electrical properties (ρ= 2.6 × 107 Ω cm at 500 °C and 1.8 × 106 Ω cm at 600 °C, k p = 6.1%–6.2% at RT ∼ 500 °C), which demonstrates that the Nd-modified CBN ceramics are promising piezoelectric materials for use in HT piezoelectric sensors.

A Systematic Review on the Dielectric Response of Polyvinyl alcohol - Zinc Oxide Nanocomposites Films

This review article mainly discusses about the dielectric properties of polyvinyl alcohol (PVA)-zinc oxide (ZnO) nanocomposites films. Nanostructured ZnO is a semiconducting functional material. It has received a significant amount of attention due to its potential applications in various areas like antimicrobial, optoelectronic and sensor devices. Polyvinyl alcohol on the other hand offers an insulting polymer matrix with good dielectric breakdown strength and film forming properties. Incorporating semiconducting ZnO nanostructures into the insulating PVA matrix is of contemporary interest due to the intriguing dielectric response of the resulting nanocomposite films. Literature reports on the variations of several electrical parameters such as real and imaginary part of the complex permittivity, AC conductivity and complex impedance have been analysed here systematically. The effect of different ZnO nanostructure loading weight percentages, measurement temperature and frequency variations have been correlated with the corresponding changes in the dielectric constant, loss tangent values, dc conductivity contribution regime, hopping frequency, relaxation time and prevailing ac conduction mechanism of the nanocomposite films. Thus, this systematic review aims to provide a roadmap for the scientific community to optimize different parameters and enhance the functional properties of the PVA-ZnO nanocomposite films.