Non-overlapping Small Polaron Tunneling Research Articles

Investigation of structural, morphology, optical properties and electrical transport conduction of Li0.25Na0.75CdVO4 compound

Polycrystalline Li0.25Na0.75CdVO4 was synthesized via a solid-state technique under air atmosphere. It is found that X-ray diffraction peaks are listed as orthorhombic Na2CrO4 structure belonging to the space group Cmcm. Composition of elements was examined by energy dispersive X-ray analysis (EDX or EDS). Grains size and morphology of the present material were investigated by scanning electron microscopy (MEB) and atomic force microscopy (AFM). Electrical measurements were performed using complex impedance spectroscopy. Impedance curves confirm the presence of two contributions and an equivalent circuit was suggested. An electrical transport in the material as a thermally activated process has been achieved using DC conductivity. While; AC conductivity is analyzed by the non-overlapping small polar on tunneling (NSPT) conduction mechanism. Refractive index, extinction coefficient, and band gap energy were determined from ellipsometric measurements.

Synthesis and thermal stability, electrical conductivity and dielectric spectroscopic studies of poly (ethylene-co-vinyl alcohol)/graphene oxide nanocomposite

A new nanocomposite was successfully synthesized by incorporating the prepared graphene oxide into poly(ethylene-co-vinyl alcohol) (EVOH) copolymer via simple solution casting method. XRD, FT-IR, SEM and TGA analysis were used to characterize the current nanocomposite. AC electrical transport properties of the nanocomposite were studied in the frequency range (10 Hz-1MHz) over the temperature range (298–423 K). The AC conductivity results were interpreted using jump relaxation model and were found to obey the universal double power law. The conduction mechanism inside the current samples has changed from non-overlapping small polaron tunneling to correlated barrier hopping. The calculated barrier height has indicated that the predominant charge carriers in the EVOH/GO nanocomposite are the single polarons and not bipolarons. The enhancement in σac of the EVOH-based nanocomposite, making these samples highly recommended for use in energy storage applications such as; electronic capacitors where materials with high dielectric constant and low dielectric loss are required.

Electrical conductivity and vibrational studies induced phase transition in [N(C3H7)4]2ZnBr4 compound

Bis-Tetrapropylammonium tetrabromozincate was synthesized and characterized by X-ray powder diffraction, as well as vibrational and impedance spectroscopy. Rietveld’s refinement of X-ray diffractogram confirmed the crystallization of the compound through the monoclinic system (space group [Formula: see text]. A temperature study of Raman scattering revealed two phase transitions at approximately [Formula: see text] = 340 K and [Formula: see text] = 393 K. The wavenumber and the line width’s evolution as a function of temperature showed some peculiarities associated with these transitions, which suggests that they are governed by the reorientation of the organic part [N(C3[Formula: see text]][Formula: see text]. The complex impedance plotted as a double semicircular arc in the studied temperature range and the centers of these semicircles lie below the real axis, which indicates that the material is an on-Debye type. These semicircular arcs are related to the bulk and the grain boundary effects. Furthermore, the alternating current conductivity of [N(C3[Formula: see text]]2ZnBr4 obeyed Jonscher’s law: [Formula: see text] = [Formula: see text] and the conduction could be attributed to the correlated barrier hopping (CBH) model in both region(I) and (II) and the Non-overlapping Small Polaron Tunneling (NSPT) in region (III).

Structural phase transition, vibrational analysis, ionic conductivity and conduction mechanism studies in an organic-inorganic hybrid crystal: [N(CH3)3H]2CdCl4

Hybrid organic-inorganic metal halides (HOMHs) present good application prospects in optoelectronics and photovoltaic as a result of their richness in physical properties and diverse structural assemblies. Herein, the organic-inorganic hybrid compound, [N(CH3)3H]2CdCl4 (1) is successfully synthesized by slow evaporation at room temperature. X-ray powder diffraction shows that 1 crystallizes in the orthorhombic system with the space group Pna21. The chemical composition of 1 is discussed by a STEM−EDS. Two-phase transitions at T1=253/263 ​K and T2=290/300 ​K are confirmed by the differential scanning calorimetry (DSC) curve. The measurements of the electrical properties are performed in the 10−1−107 ​Hz frequency range and 220−335 ​K temperature interval. The study on the charge transfer mechanism of 1 is done with the help of Elliott’s theory. The conduction mechanism in 1 is interpreted by different approaches: the correlated barrier hopping (CBH) model in phase I, the non-overlapping small polaron tunneling (NSPT) model in phase II, and the overlapping large polaron tunneling (OLPT) model in phase III.

Study of charge transfer mechanism and dielectric relaxation of all-inorganic perovskite CsSnCl3.

In the field of commercialization, lead-free metal halide perovskite materials are becoming more popular these days because of their prospective use in solar cells and also in other optoelectronic applications. In this paper, a non-toxic CsSnCl3 metal halide is successfully synthesized via the slow evaporation solution growth technique. Such systematic characterizations as differential scanning calorimetry (DSC) measurements, dielectric measurements, and variable-temperature structural analyses indicate that CsSnCl3 goes through a reversible phase transformation at T = 391/393 K from the monoclinic to the cubic system. Optical measurements of CsSnCl3 reveal a direct band-gap value of about 3.04 eV. The study of the charge transfer mechanism of CsSnCl3 is carried out based on Elliott's theory. The conduction mechanism in CsSnCl3 is interpreted through the following two approaches: the non-overlapping small polaron tunneling (NSPT) model (monoclinic phase) and the overlapping large polaron tunneling (OLPT) model (cubic phase). Moreover, the high dielectric constant of CsSnCl3 which is associated with a low dielectric loss makes it a possible candidate for energy harvesting devices.

Impact of Ni doping on the morphological, electrical and dielectric properties of YMn0.4Fe0.6-xNixO3 (0 ≤ x ≤ 0.1) multiferroics

The impact of Ni doping on the morphological, electrical and dielectric properties in a polycrystalline sample of YMn0.4Fe0.6O3 was investigated. SEM analysis reveals that grain size increases with the rise of Ni concentration in YMn0.4Fe0.6-xNixO3 (x = 0, 0.05, 0.075 and 0.1) nanoparticles up to x = 0.075. The DC conductivity results indicate that all samples exhibit semiconductor behavior over the whole studied temperature range (240–440 K). In addition, the σDC curves show that the conductivity follows the same trend of the grain size with doping. AC conductivity measurements (σAC) are found to obey to Jonscher's universal power law. Actually, the results show that non-overlapping small polaron tunneling (NSPT) is the suitable model that helps to understand the conduction mechanism in our samples. Moreover, the contribution of both grain and grain boundaries in the conduction process is proved by Nyquist spectra which were fitted by an appropriate equivalent circuit. Based on dielectric measurements, it is found that dielectric losses are ruled by the DC conduction process.

Enhanced electrical conductivity in Zr-Doped (La0.7Ba0.3)(Mn0.5Fe0.5)O3 solid solutions

The perovskite ([Formula: see text][Formula: see text]([Formula: see text][Formula: see text][Formula: see text]O3, where [Formula: see text] = 0.1, 0.2 and 0.3, ceramics were synthesized by solid-state reaction method. The introductory structural studies were followed through by X-ray diffraction technique and the results have disclosed that all the samples were crystallized into an isolated phase. The Zr substitution in the resulting solid solutions increases the electrical conductivity and the maximum value of ac conductivity has been found to be [Formula: see text]118.8 S [Formula: see text] cm[Formula: see text] for [Formula: see text] = 0.3 at 200[Formula: see text]C (at 1 MHz). The frequency dependence of ac conductivity data follows Jonscher’s power law. The variation of the exponent [Formula: see text] versus temperature follows the nonoverlapping small polaron tunneling (NSPT) model. The dielectric relaxation has been observed to be of non-Debye nature for all measuring temperatures (50–200[Formula: see text]C). The impedance spectroscopy reveals that all the samples exhibit negative temperature coefficient of resistance (NTCR) behavior. The prepared samples (for [Formula: see text] > 1) are supposed to be suitable for cathode materials in SOFCs.

Investigation of optical properties and electrical conductivity mechanism of Fe2O3–Sm2O3–ZnO–P2O5 quaternary glass nanocomposite systems

The influence of incorporation of Fe2O3 on the physical, structural, optical, and electrical properties of zinc-samarium phosphate glasses synthesized via conventional melt quenching technique have been studied. The polycrystalline nature, crystallinity percentage, and average size of the developed nanocrystallites in the as-prepared samples have been determined from the obtained X-ray diffraction data. TEM micrographs and SAED patterns confirm the formation of nanocrystallites over the amorphous glassy network. EDX spectra reveal the weight and atomic percentage of each constituent element. Density and molar volume data show inverse relation, which has been explained by the formation of non-bridging oxygens. The optical bandgap energy (Eopt) values, obtained from UV-Vis spectroscopic data, and the calculated Urbach energy (EU) values reduce with increasing Fe2O3 concentration (x). The Fe2O3 concentration (x) dependent refractive index, electronic polarizability, molar refraction, oxide ion polarizability, optical basicity, and electronegativity have been determined. Mott's variable range hopping model is used to explain the DC conduction mechanism, whereas the non-overlapping small polaron tunneling model is used to explain the AC conduction mechanism. Both the AC and DC conductivity are found to increase with the incorporation of Fe2O3. The scaling property of AC conductivity reveals that the conductivity relaxation process depends on the structural composition of the present sample but is independent of temperature.

VRH and NSPT conduction mechanisms in CuIn0.7Ga0.3Se2 near the liquid nitrogen temperature

Variable range hopping conduction process of Shklovskii-Efros type is identified, for the first time, in CuIn0.7Ga0.3Se2 bulk material in the temperature range [-190 °C, −10 °C]. Two different methods are considered to confirm this mechanism. The corresponding characteristic temperature and the localization length of mobile carriers are estimated. The AC electrical conductivity analysis suggests the predominance of Non-overlapping Small Polaron Tunneling mechanism. In the frequency range [20 Hz, 1 MHz], the equivalent circuit model of this material is established and the microscopic contributions to the total electrical conduction are discussed.

Usefulness of theoretical approaches and experiential conductivity measurements for understanding manganite-transport mechanisms

Experimental measurements and numerous theoretical models have been employed to comprehend the dynamics of charge carriers in manganite system. The present work highlights the electrical transport of La0.5Ca0.4Ag0.1MnO3 compound in the temperature range [80 K–700 K]. It is found that the conductivity spectra of the studied sample present a double Jonscher variation, universal Jonscher evolution and Drude variation respectively for low, intermediate and high temperature ranges. The temperature dependence of the frequency exponent confirms the efficiency of the quantum mechanical tunneling, the non-overlapping small polaron tunneling and the correlated barrier hopping mechanisms at separated dispersive regions. DC conductivity analysis confirms the semiconductor behavior of the studied sample. Then, the transport properties have been explained in term of a thermally activated small polaron hopping and Mott-variable range hopping processes respectively at high and low temperature sides. Also, the disorder energy is predicted to decrease with rising frequency which could be due to variation in the separation path between the hop centers. Moreover, Greaves variable range hopping model is the suitable one that describes the transport properties in the intermediate temperature range. The scaling approach indicates that the time temperature superposition principle is valid in the temperature side [180 K–360 K].

Crossover from overlap large polaron to small polaron tunneling: A study of conduction mechanisms and phase transitions in a new long chain organic inorganic hybrid

AC-conductivity study of the new long chain hybrid [NH3 (CH2)8 NH3]Cl2 in the temperature range 210 K–420 K showed the following consecutive phase transitions:(PhaseVIII)T7=232.5K(PhaseVII)T6=253K(PhaseVI)T5=287.9K(PhaseV)T4=316.5K(PhaseIV)T3=330.7K(PhaseIII) T2=378.8 K(PhaseII)T1=399 K(PhaseI).Transitions are confirmed by differential scanning calorimetry (DSC). Room temperature X-ray powder diffraction indicated a monoclinic P21/c with crystallographic parameters a = 18.179 Å, b = 15.380 Å, c = 4.881 Å and β = 109.54(0), V = 1286 (Å)3, Z = 4. Frequency dependent ac-conductivity at different temperatures is interpreted in terms of the jump relaxation model and is fitted to super-linear power law σtot = σdc + A1ωs1+ A2ωs2. The fit parameters lnA1/s1 and lnA2/s2 are sensitive to the type of conduction mechanism. Temperature and frequency dependence of ac-conductivity indicated that in the low (T < 231 K) and intermediate (290 K–316 K) temperature ranges, conduction takes place via quantum mechanical tunneling (phases (VIII) and (V)). Crossover from large polaron to non-overlapping small polaron tunneling takes place associated with transition from phase (VII) to phase (VI). Correlated barrier hopping (CBH) prevails at high temperature (phases (I, II, III and IV)). Activation energy and its frequency dependence were calculated for the different phases. Minimum tunneling and hopping distances, effective barrier height WM as well as the density of states at the Fermi level (N(Ef)) were evaluated from ac-conductivity results.

Crystal structure and electrical conduction mechanism of the new bi-tetrabutylphosphonium hexachlorostannate compound

The bi-tetrabutylphosphonium hexachlorostannate [P(C4H9)4]2SnCl6 compound is a new member of the family of organic-inorganic hybrid like perovskite system. This compound crystallizes in the monoclinic space group C2/c with unit cell parameters a = 14.4008 Å, b = 18.7256 Å, c = 17.5135 Å and β=113.1780° The (SnCl6)2− anions are surrounded by six [(C4H9)P]+ cations, forming an octahedral configuration. Regarding the differential scanning calorimetry, three order- disorder reversible phase transitions were observed at T1 = 388/363 K, T2 = 403/395 K and T3 = 446/410 K. Analysis of frequency and temperature dependence of impedance and electrical modulus spectroscopic data and Nyquist plots has shown the contributions of grains and grain boundaries to the electrical properties of the prepared material. The variation of the dielectric loss log (ε ‘’) with log (ω) is found to follow the empirical law, ε’’= Bωm(T). Moreover, the temperature dependence study of frequency exponent m (T) is investigated toexplain the conduction mechanism in the different parts, which is attributed to the non overlapping small polaron tunneling (NSPT) in the region I, II and III and by the correlated barrier hopping (CBH) model in phase IV.

Frequency and temperature impact on the electrical properties of LaCr0.99Pd0.01O3-ẟ compound

The LaCr0.99Pd0.01O3 compound has been synthesized with solid-state reaction method. The microstructure, crystalline structure, chemical composition, and oxidation states of elements were investigated via SEM, Raman and XPS analysis techniques. SEM has revealed that particles have various sizes. XPS investigation has unveiled the oxidation states of La (3+), Pd (4+), and Cr (both 3+ and 6+). Electrical characterization has been performed in nitrogen ambient using Novocontrol Dielectric Spectrometer. Real and imaginary parts of the dielectric function, impedance, modulus, and conductivity of studied compound were investigated in wide temperature and frequency range. The activation energy from the log fmax vs. (kT)−1 and log σdc vs. (kT)−1 plots has been obtained as 0.240 eV and 0.231 eV, respectively. It has been demonstrated that the correlated barrier hopping (CBH) and non-overlapping small polaron tunneling (NSPT) conductions take place in the LaCr0.99Pd0.01O3 compound.

Effects of sintering temperature on structural, infrared, magnetic and electrical properties of Cd0.5Zn0.5FeCrO4 ferrites prepared by sol–gel route

In this work, an attempt is made to study the effects of sintering temperature on the structural, infrared, magnetic and electrical properties of Cd0.5Zn0.5FeCrO4 ferrites. Samples were prepared by sol–gel route and sintered at 900 and 1100 °C. The structural characterization of the synthesized powders by X-ray powder diffraction showed that only single phase with cubic spinel structure existed. Estimated values of unit cell parameter and average grains size show an increase with sintering temperature. The intensities of absorption bands, spontaneous magnetization, electrical conductivity, and dielectric constants were found to increase with increasing sintering temperature. The non-overlapping small polaron tunneling (NSPT) model dominates the conduction process for the studied samples which present a relaxation phenomenon with non-Debye nature. Close activation energies values were found from analyzes of relaxation time and dc-conductivity indicating that the relaxation and the conduction processes may be attributed to the same type of charge carriers. The equivalent electrical circuit (Rg+ Rgb//CPEgb) was used for modeling the Nyquist data.

Effect of doping in the physico-chemical properties of BaTiO3 ceramics

Barium titanate is a very attractive perovskite given its ferroelectric, piezoelectric and dielectric properties. These can be further improved by the substitution of barium and titanium by different elements. Introducing both rare earths and/or metals in this compound enhances its optical and electrical properties, thus making it a multifunctional material suitable for many different applications. In the present work, the compound Ba0·91Er0·1/3Ca0·04Ti0·92Sn0·08O3 is prepared by solid state reaction and its structural, morphological, thermal optical and electrical properties are investigated in detail by X ray diffraction, scanning electron microscopy, differential scanning calorimetric, absorption spectroscopy and impedance spectroscopy respectively. Scanning electron microscopy shows that the material is composed by a major polycrystalline phase with micrometric grain size. Two-phase transitions at 448 K and 572 K are deduced from thermal and electrical measurements. The optical measurements indicate that both erbium and tin are well introduced in the structure, which is confirmed by energy dispersive spectroscopy, and affects the vibrational modes. a. c. and d. c. electrical measurements show that, depending on the measurement temperature range, conduction mechanism is either a non-overlapping small polaron tunneling or a correlated barrier hopping model. . Moreover, dielectric measurements prove a high dielectric constant and identify a phase transition from the ferroelectric phase to paraelectric one which is in agreement with literature. Such substitution improves the compound properties and makes it suitable for different devices.

Studies of electric, dielectric properties, and conduction mechanism of {(C2H10N2)(MnCl (NCS)2)2}n polymer

AbstractDielectric and electrical properties correlated with the structure analysis have been studied for new crystalline polymer {(C2H10N2)(MnCl (NCS)2)2}n. The frequency and temperature dependence of dielectric constant (ε′), dielectric loss (ε″) and loss tangent (tanδ) in the temperature range 308‐348 K and frequency range 20 to 2 MHz have been made for {(C2H10N2)(MnCl (NCS)2)2}n. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The analysis of Nyquist plots is well fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. The spectra follow the Arrhenius law with two activation energy the first in the region of temperatures before 332 K (Region I) and the second in the region after 332 K (Region II). An agreement between the experimental and theoretical results is discussed, and it is suggested that the ac conductivity can be explained by the correlated barrier hopping (CBH) and nonoverlapping small polaron tunneling model (NSPT) in regions I and II, respectively. The AC conduction mechanism is governed by the correlated barrier‐hopping (CBH) with WM (Region I) = 270 meV and a tunneling distance of 4.5 Å, whereas it becomes a small polaron tunneling mechanism (SPTM) mechanism with a WH (Region II) = 153 meV. The imaginary part of the electrical modulus formalism obeys the Kohlrausch‐Williams‐Watt (KWW) model. The theoretical Kohlrausch exponent (βKWW) confirms the existence of the transition phase on the new crystalline polymer in the vicinity of the 332 K as deduced by the DC and the AC conduction parameters. Thus, the near values of activation energies obtained from the impedance and modulus spectra confirm that the transport is through an ion hopping mechanism.

Investigation of the conduction mechanism, high dielectric constant, and non-Debye-type relaxor in La0.67Ba0.25Ca0.08MnO3 manganite

The conduction mechanism and electric properties of La0.67Ba0.25Ca0.08MnO3 (LBCM) were analyzed depending on temperature and frequency. The frequency dependence of electrical conduction plot was explained by the jump relaxation model. The electrical conduction process was based on both theoretical conduction models assigned to the Correlated Barrier Hopping and Non-overlapping Small Polaron Tunneling mechanism. The impedance plot studies reveal that the relaxation is a non-Debye poly-dispersive pattern in the LBCM. This compound has excellent dielectric properties such as the dielectric permittivity exceeding 105 at room temperature, i.e., colossal permittivity, and is one of the highest values recorded for ceramic capacitors. Thus, evolution of dielectric permittivity, described in terms of spatial charge polarization based on Koop's phenomenological theory and Maxwell–Wagner's (M– W) model and high dielectric response, has been driven by barrier layers into the grain boundaries and blended structures of Mn3+/Mn4+. The relaxation processes were examined with modulus, impedance formalism, and electrical conductivity. In the thermal analysis, the relaxations mechanism are related oxygen vacancies.

Temperature-dependent transport properties of micro and nano-sized zinc cobalt oxide (ZnCo2O4) and zinc manganese oxide (ZnMn2O4) particles synthesized by a hydrothermal route

In the present work, a hydrothermal method has been adopted to synthesize micro (~150 nm), and nano (~20 nm) particles of Zinc based, cobalt, and manganese oxide structures, i.e., ZnCo2O4 (ZCO) and ZnMn2O4 (ZMO). These structures have been examined by X-ray diffraction, Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The effect of different reducing agents and solvents have been ascertained on the morphological and the crystalline nature of the samples. The highly crystalline and micron-sized particle formation has been observed with the usage of NaBH4 as the reductant in the water solution, and a polycrystalline structure with nanosized particle formation has been found with NaOH as the reductant in the water and DMF solution. The electrical properties have been investigated between 100 Hz and 1 MHz by varying the temperature from 303 K to 513 K. The micro and nano sized particles of ZCO and ZMO have shown frequency dependence, thermally activated and relaxation-type dielectric behavior confirming the semiconducting nature. The variation of ac conductivity with frequency at different temperatures is according to Jonscher's power law for micro and nano sized particles of the ZCO and ZMO but supporting different conduction mechanisms. The conduction mechanism in microparticles and nano-particles is according to an overlapping-large polaron tunneling (OLPT) model, and the Non-overlapping small polaron tunneling (NSPT) model, respectively.

The sodium-ion battery: Study of alternative current conduction mechanisms on the Na3PO4 - Based solid electrolyte

Abstract Sodium-ion batteries have been dominating as a power source in digital cameras, laptop computers, mobile phones and electric/hybrid electric vehicles. This can be explained by their high life cycle and power density which differentiate them from other battery types. Sodium phosphate is considered among the favored solid electrolyte materials for the sodium-ion battery because of its high ionic conductivity. In this study, Na3PO4 was obtained using the classic ceramic method and characterized by X-ray powder diffraction patterns, infrared spectroscopy, differential scanning calorimetry (DSC) and electrical impedance. The Na3PO4 compound crystallized at room temperature in the tetragonal system with a P 4 ‾ 2 1 c space group. The morphology and composition of Na3PO4 were studied by a scanning transmission electron microscope coupled with the energy dispersive X-ray spectroscopy (STEM-EDS). The phase transition at T1 ≈ 603/605 K was confirmed by the differential scanning calorimetry (DSC). Infrared spectroscopy confirmed the presence of the (PO4)3− group and its vibrations. The electrical technique was measured in the 10–106 Hz frequency range and 540–700 K temperature intervals. The frequency dependence of alternative current conductivity was explained using Jonscher law. The alternative current electrical conduction in Na3PO4 was interpreted through several processes, which could be associated with two different models: the overlapping large polaron tunneling (OLPT) model in phase I and the non-overlapping small polaron tunneling (NSPT) model in phase II. The conduction mechanisms of Na3PO4 were explained by Elliott's theory and consequently the Elliott's parameters were calculated.

Thermal transport and electrical properties of Se95-xSn5Bix (x = 0, 4, 8) chalcogenide alloys

This study reports the structural, thermal-transport and electrical properties of the Se95-xSn5Bix (x = 0, 4, 8) chalcogenide alloys. The x-ray diffraction analysis (XRD) reveals the polycrystalline nature of samples. Transmission electron microscopy (TEM) demonstrates the formation of nano-rods and clusters of nano-particles. Differential scanning calorimetry (DSC) of the samples, x = 4&8 indicates, there may be two co-existed phases in these samples. Thermal conductivity (λe) shows a decreasing trend with the inclusion of Bi in Se–Sn system. Thermal diffusivity (χe) and volumetric heat capacity (QCp) show the optimum value for x = 4. Thermal transport parameters remain almost temperature independent. The dielectric constant/loss decreases with frequency and increases with temperature. Maximum dielectric constant/loss is obtained for the un-doped sample, while for doped samples, the values have decreased with Bi content. The strong dependence of conductivity over temperature is explained in terms of non-overlapping small polaron tunneling (NSPT) for undoped and CBH models for Bi doped samples.