Non-overlapping Small Polaron Tunneling Research Articles

Temperature dependent electrical transport behavior of (100-x)Bi2O3-x(BaTiO3) glass system

Impedance measurements were performed as a function of temperature (RT to 700 K) in the frequency range (1 Hz-1MHz) on fabricated Bismuth Barium Titanate glass samples. Dielectric permittivity is found to be increased on increasing both the temperature and BaTiO3 (BT) content in highly polarizable glass matrix of Bi2O3. Experimental data obtained for imaginary part of electric modulus (M″)has been fitted theoretically using non-exponential Kohlrausch-Williams-Watts (KWW) function, however Jonscher's universal power law has been employed to analyze the frequency dependent ac conductivity. The calculated activation energy values for both the samples have been found to be in close agreement with each other and qualify for doubly ionized oxygen vacancies, proposing that the similar kind of charge carriers are involved in the relaxation and conduction mechanisms. Stretched exponent (β) of Modulus and power exponent (n) of ac conductivity, estimated from theoretical fitting of experimental data, have been found to be dependent on temperature and BT (BaTiO3) content. On increasing temperature, an increase in values of (n) suggests that non-overlapping small polaron tunneling (NSPT) model can be easily applied to explain ac conduction and hopping transport mechanisms of the fabricated glass samples.

Structural, optical, and dielectric properties for Mg0·6Cu0·2Ni0·2Cr2O4 chromite spinel

In this work, the structural, optical, and dielectric properties for Mg0·6Cu0·2Ni0·2Cr2O4 chromite sample prepared by sol-gel process were investigated. The XRD characterization for this sample confirmed the development of the face-centered cubic spinel structure with Fd3‾m space group. From the UV–Vis optical absorbance, the synthesized chromite shows significantly lower direct band gap energy and has an appropriate absorption rate in the visible light region. The variations of penetration depth, extinction coefficient, refractive coefficient, dispersion energy parameters, and dielectric permittivity constants were also interpreted. The Non-Overlapping Small Polaron Tunneling (NSPT) and the Correlated Barrier Hopping (CBH) are the suitable models to describe the conduction process for the prepared sample. The behavior of dielectric constants has been interpreted based on the Maxwell-Wagner's theory of interfacial polarization. The behavior of imaginary part of impedance (Z″) shows a dielectric-relaxation phenomenon in the sample with activation energies near to those determined from the conductivity study.

Structure, small polaron hopping conduction and relaxor behavior of Gd2NiMnO6 double perovskite

In this study, double perovskite Gd2NiMnO6 is prepared via auto–ignition method. Rietveld refinement of the XRD profile confirms the single phase monoclinic structure with space group P21/n. The cation Ni exhibits mixed valence state (+2/+4) and Mn exhibits +4 valence state. Grain, grain boundary and dc conductivity increase with temperature indicating the semi–conductive nature of the material. The grain conductivity is much higher and activation energy for grain conductivity is much lower than the grain boundary. The activation energy for dc conduction and hopping energy are almost identical at different temperature regions. The charge conduction mechanism follows non–overlapping small polaron tunnelling (NSPT) model. Different Mott's parameters confirm small polaron hopping. The polaron hopping mechanism is non–adiabatic in nature. Time–temperature superposition principle confirms the temperature independent nature of hopping mechanism. The value of electron photon coupling constant is 8.27 which confirms the strong electron–phonon coupling in this material. The dielectric relaxor behavior is found to follow modified Curie–Weiss law which becomes more conform with frequency. The value of co–efficient of diffuseness lies in the range 1.69–1.96 which confirms the diffuse behavior of the material.

Frequency and temperature dependent electrical characteristics of P-doped nc-SiOX:H thin films

Phosphorus-doped nc-SiOX:H films with elevated dark-conductivity and wide optical band gap are prepared via one-step low-temperature (~ 250 °C) processing, by optimizing H2-dilution [RH = H2/(He + H2)] of the (SiH4 + CO2 + PH3) precursor gasses in RF plasma-CVD. The band tail defect dynamics in covalently bonded disordered oxide-semiconductor system has been extensively studied via frequency and temperature dependent conductivity-response, impedance-characteristics, and dielectric-properties, in doped-silicon-oxygen and amorphous-nanocrystalline complex system. The temperature dependent ac-conductivity obeys the Universal Jonscher power-law and the behaviour of extracted parameters from nonlinear-fitting identifies non-overlapping small-polaron-tunnelling (NSPT) model to prevail in ac-conduction mechanism. Modelling of the impedance spectra over wide frequency range via equivalent electric circuit consisting of two parallel R||CPE connected serially, confirms individual contribution of separate nc-Si and a-SiOX:H moieties. The charge carrier density-of-states, N(EF), participating in ac-conduction at ~ 373 K and ~ 104 Hz increases from ~ 7.6 × 1015 eV−1cm−3 to ~ 1.4 ×1017 eV−1cm−3 with RH elevated from 0.1 to 0.4, corresponding to increased O-content simultaneous to reduced H-content in the Si-network possessing sequentially higher-crystallinity and wider optical band gap.

Study of Charge Transfer Mechanism and Dielectric Relaxation of CsCuCl3 Perovskite Nanoparticles

Non-toxic inorganic metal halide perovskites have commercially established dominance over all the other optoelectronic devices. In this paper, a non-toxic CsCuCl3 metal halide is successfully synthesized through the slow evaporation solution growth technique. The hexagonal phase of the material is checked using the X-ray diffraction measurement. The morphological study indicates the spherical shape of nanoparticles with about 20 nm size. CsCuCl3 demonstrates a semiconducting property with a direct band gap value of approximately 2.18 eV. Over the 10−1–107 Hz frequency range, the dielectric constant, the loss factor, the electric modulus and also the electrical conductivity of CsCuCl3 show strong temperature dependence. The Nyquist plot confirms the various contributions of grains and grain boundaries to the total impedance. In the high-frequency region, the dielectric constant tends to increase with temperature. The modified Cole–Cole plot asserts that while the relaxation time decreases with the rise in temperature, the space charge and free charge conductivity increase the moment the temperature climbs. In accordance with the modified Kohlrausch-Williams-Watts (KWW) equation, an asymmetrical nature corresponding to the non-Debye type of the perovskite is noticed in the electric modulus spectra at different temperatures. Moreover, the imaginary part of the electric modulus spectra is found to shift from the non-Debye toward the Debye type with the increase in temperature despite not getting the exact Debye response and emerging as a semi-conductor material. The alternating current (AC) conductivity of CsCuCl3 is shown based on the non-overlapping small-polaron tunneling (NSPT) mechanism. The fact that the direct current (DC) conductivity matches well with the activation energy which is based on the two modulus spectra indicates that the relaxation behavior and the conduction mechanism are remarkably similar. Additionally, CsCuCl3 is likely to be an energy-harvesting device since it has a high dielectric constant related to its low dielectric loss.

The lithium-ion battery: Study of alternative current conduction mechanisms on the Li3PO4 - based solid electrolyte

Lithium-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. Lithium phosphate is considered among the favored solid electrolyte materials for the lithium-ion battery because of its high ionic conductivity. In this study, Lithium phosphate (Li3PO4) compound was obtained by the classic ceramic method. The X-ray powder diffraction pattern indicates that at room temperature, Li3PO4 crystallized in the orthorhombic system with Pnma space group. The morphology and composition of Li3PO4 were performed by scanning transmission electron microscope coupled with energy dispersive X-ray spectroscopy (STEM-EDS). Infrared spectroscopy was confirmed the presence of (PO4)3− anion and its vibrations. The measurements of the electrical properties were performed in the 100 Hz to 1 MHz frequency range and 528–713 K temperature intervals. The interpretation of Nyquist curves revealed the presence of three electrically active areas equivalent to the electrode processes, distribution of grain boundaries and bulk mechanism. The alternative current electrical conduction in Li3PO4 was interpreted through several processes, which can be associated to two different models: the non-overlapping small polaron tunneling (NSPT) model in the region I and the overlapping large polaron tunneling (OLPT) model in the region II. Elliot's theory was used to interpret the conduction mechanism, and all Elliot's parameters were determined.

Conduction mechanisms and relaxation phenomena along with electronic transition of ZnO/ZnNb2O6/Nb2O5 composite

This paper deals with the study of the physical properties of ZnO/ZnNb2O6/Nb2O5 composite. X-ray diffraction (XRD) proves the coexistence of hexagonal ZnO, tetragonal Nb2O5 and orthorhombic ZnNb2O6. Scanning electron microscopy (SEM) observations reveals heterogenic distribution of grains with average size of about 456 nm. The dielectric measurements are performed in 20 Hz–1MHz frequency range between 150 °C and 350 °C. Theoretical fit demonstrates that the electric resistivity, associated to grains and grain boundaries, decreases as a function of temperature up to 275 °C. At 275 °C, the composite presents a semiconductor-metal transition, confirmed by the temperature-dependence of DC conductivity. Moreover, the AC conductivity variations suggest that the AC conduction mechanisms are explained by the Quantum-Mechanical Tunneling (QMT) model below 275 °C and the Non-Overlapping Small Polaron Tunneling (NSPT) one above 275 °C. Also, the activation energies, related to dielectric relaxation processes and DC conductivity, are almost equal: Ea ~ 0.53eV in the interval 150 °C < T < 275 °C, and Ea ~ −0.47eV for T > 275 °C. Moreover, the permittivity variations show the existence of interfacial Maxwell-Wagner-Sillars (MWS) and dipolar polarization.

The effects of N2 atmosphere annealing on the physical properties of BiFe0.5Mn0.5O3 ceramic

Multiferroic BiFe0.5Mn0.5O3 (BFMO) was elaborated by the conventional solid-state method under ordinary sintering conditions (air) and N2 atmosphere at 1193 K, and the effects of the two different atmospheres on the structural properties were studied. Indeed, it was found that BFMO prepared in the atmospheric air exhibited an impurity phase, BFMO annealed under an N2 atmosphere, displayed an intensity of secondary phase that decreased significantly (As for the Rietveld analysis), indicating that BFMO annealed under N2 flow crystallized in rhombohedral structure with R3c space group. The phase crystallinity was confirmed by Raman spectroscopy. Moreover, a dielectric study revealed the enhancement of dielectric permittivity ε’r and a low dielectric loss. Concerning the electrical hysteresis loop at room temperature, it indicated that BFMO sample exhibited ferroelectric characteristics. Besides, the impedance spectroscopy and conductivity were investigated in the frequency range of 102-106 Hz. Nyquist plots indicated the presence of only grain contributions. Furthermore, the conduction mechanism was evaluated by Ac conductivity using Jonsher low. From the thermal variation of the exponent S, it was concluded that the model of Correlated Barrier Hopping (CBH) and the Non-overlapping Small Polaron Tunneling (NSPT) were the dominant conduction mechanisms present in our sample. From the magnetic measurement, FC and ZFC were reported to show the weak ferromagnetism character of our sample. The obtained physical properties of BFNO at room temperature suggest that this material can be used in technological applications.

Investigation on Non-Debye type relaxation and polaronic conduction mechanism in ZnCr2O4 ternary spinel oxide

Ternary spinel chromite ZnCr2O4 was synthesized by sol-gel auto-combustion method. Rietveld profile analysis of X-ray powder diffraction data revealedthe cubic spinel crystal structure with Fd-3 m space group. Thedielectric relaxation and transport behavior of ZnCr2O4were studied in detail by complex impedance spectroscopy in the frequency range of70-1.1x106Hzover the measured temperature range of293-523K. Nyquist plots modeled by the equivalent circuit RG‖QG+RGB‖QGBindicated the presence of two relaxation processes in the material. The AC conductivity followed Jonscher power law and variation of frequency exponent with temperature depicted non-overlapping small polaron tunneling as a dominant electrical transport mechanism in the sample. Moreover, the DC conductivity obeyed Mott and Davis law. The frequency and temperature dependence of dielectric constant and loss factor was discussed in terms of space charge polarization, Maxwell-Wagner type dielectric relaxation and hopping of charge carriers between Cr2+ and Cr3+networks in ZnCr2O4 system.

Investigations of microstructural and impedance spectroscopic properties of Mg0.5Co0.5Fe1.6Al0.4O4 ferrite prepared using sol–gel method

Polycrystalline Mg0.5Co0.5Fe1.6Al0.4O4 ferrite was prepared using sol–gel method. This sample was characterized by powder X-ray diffraction (XRD), Scanning electron microscopy, and impedance spectroscopy. XRD analysis combined with the Rietveld refinement confirmed the cubic-spinel structure (SG: \(Fd\stackrel{-}{3}m\)) for the prepared sample. Electrical conductivity obeying the Jonscher power law indicates that the prepared material exhibits semiconductor behavior, and the conduction process follows the “non-overlapping small polaron tunnelling, NSPT” model between neighbors’ sites. The behavior of dielectric constants such as permittivity and loss coefficient has been interpreted based on the Maxwell–Wagner’s theory of interfacial polarization. The curves of imaginary parts of impedance (Z″) and modulus (M″) show dielectric-relaxation phenomenon in the sample with activation energy near to that determined from the dc conductivity study. Nyquist plots (− Z″ vs. Z′) show a monotonic decrease in both grain resistance (Rg) and grain boundary resistance (Rgb) with increasing temperature such as Rgb ≫ Rg. This result confirms that the transport mechanism in Mg0.5Co0.5Fe1.6Al0.4O4 compound is governed by the grain boundaries effect.

Study of dielectric relaxation and polaron conductivity mechanism in sodium nitroprusside (SNP): Na2[Fe(CN)5(NO)]·2H2O

In this study, the crystal structure of sodium nitroprusside, Na 2 [Fe(CN) 5 (NO)]·2H20, has been determined by an analysis by X-ray diffraction (XRD). The crystal is orthorhombic, space group Pnnm. This compound is characterized by different techniques: X-ray diffraction (XRD), differential scanning calorimetry (DSC) and impedance spectroscopy. For electrical properties, impedance spectroscopy was performed at a frequency range of 20 Hz–2 MHz. The dependence of AC conductivity on frequency was found to satisfy Jonscher's universal power law at different temperatures σ ( ω ) = σ D C ( ω , T ) + A ω S ( T , ω ) . This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. The temperature dependence and dielectric relaxation of the DC conductivity satisfied the Arrhenius law. The activation energy ranged from 0.033 to 0.164 eV and was similar in the conduction and relaxation mechanisms, indicating that the transport mechanisms were based on hopping phenomena. Moreover, the modulus plots has been characterized by full width at half height or in terms of a non-experiential decay function ϕ(t) = exp(−t/τ)β. The values of the activation energies obtained from the electrical conductivity and electric modulus are near; which suggests that the transport is probably due to the ion hopping mechanisms. Furthermore, this behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures. Crystal structure, Molecular Hirshfeld surfaces, hydrogen bonding, UV absorption and phase transition of the β-NH 3 (CH 2 ) 2 NH 3 SnCl 6 compound. • This compound is crystallized in the orthorhombic system (Pnnm space group). • Differential scanning calorimetric (DSC) experiments show a phase transition at 130 K and 155 K. • The conduction mechanism is attributed to the (CBH) model, (OLPT) and (NSPT) mechanism. • The activation energies suggest that the transport is probably due to the ion hopping mechanisms. • The near value of activation energies obtained from the analysis of M.

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] &gt; 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.