Polaron Hopping Conduction Research Articles

Strongly correlated electron system NiWO4: A new family of materials for triboelectrics using inherent Coulombic repulsion

The strongly correlated electron system (SCES) insulators promise a wide range of intriguing physical phenomena arising from the exotic charge gap depending on the strength of the Coulombic repulsion between d and f orbital cations. The SCES exhibits polaron hopping conduction, which requires a higher activation energy for carrier conduction between nearest cations, indicating a strong insulating character with relatively high permittivity. Here, we demonstrate that the NiWO4 SCES insulator, which is formed by Coulombic repulsion between the nearest d orbital of Ni, proposes a suitable triboelectric material unlisted system from conventional metal oxides. The higher degree of freedom in NiWO4 by the lower symmetry of monoclinic structure and an additional selection of composition exhibits high relative permittivity (∼13.8) in a wide range of temperatures (up to 180 ℃). The optimized simple mixture of NiWO4 and PDMS (polydimethylsiloxane) for the negatively charged material to triboelectric nanogenerator (TENG) presents 1.78 times higher output compared to the pristine PDMS film-based TENG. NiWO4, considering the physical properties of the SCES determined by Coulombic repulsion strength, paves the way for a new option of TENG materials following the high permittivity.

Modulation of optical absorption and electrical properties in Mn-Co-Ni-O-based high-entropy thin films

High-entropy thin films of Mn0.6Co0.6Ni0.6Mg0.6Cu0.6O4, Mn0.6Co0.6Ni0.6Mg0.6 Zn0.6O4, and Mn0.6Co0.6Ni0.6Cu0.6Zn0.6O4 (MCNMC, MCNMZ, and MCNCZ) with equiatomic proportions were synthesized using chemical solution deposition on silicon substrates. Structural analysis confirmed a consistent face-centered cubic spinel structure, while significant differences in surface morphology were observed. Quantification of the valence states of Mn ions revealed an inverse variation in the concentrations of Mn4+ and Mn2+ ions. The heightened infrared light absorption of the MCNMC thin film was assigned to Cu-induced Jahn-Teller distortion and highly polarized Mg-O bonds. All samples exhibited negative temperature coefficient behaviors in their electrical properties. Additionally, the MCNMC thin film demonstrated the lowest resistance due to its denser microstructure, close proximity of Mn3+/Mn4+ ion concentrations, and additional Cu+/Cu2+ ion pairs, enhancing small polaron hopping conductivity. In contrast, the MCNMZ thin film showed moderate resistance but boasted the highest thermal constant (B25/50) of 3768 K, attributed to its distinctive grain chain structure, facilitating carrier transport while introducing migration barriers.

Structural, dielectric and magnetic study of double perovskite La2CoMnO6

Polycrystalline double perovskite La2CoMnO6 sample was prepared via solid state reaction route and its structural, dielectric and magnetic properties were investigated. XRD confirmed the phase formation without any impurity. Rietveld refinement analysis suggested the presence of monoclinic (P21/n, ordered) as well as rhombohedral and orthorhombic (R3c &Pbnm, disordered) structures. Microstructural analysis using FESEM confirmed that average grain size lies in micrometer range. Dielectric constant (log ε′) and loss tangent (tanδ) both exhibited large values at lower frequencies as well as in higher temperature range. Nyquist impedance plot proposed NTCR (negative temperature coefficient of resistance) nature of double perovskite sample. DC conductivity showed increasing trend with increase in temperature and also, the conductivity is of the order of 10−2 S/m, which represent semiconducting behavior of prepared sample. Also, the analysis suggested the co-existence of thermal activation (TA), small polaron hopping (SPH) and variable range hopping (VRH) conduction mechanisms. Temperature dependent magnetic measurements (M-T) suggested that sample exhibit single magnetic transition at 226 K. Field dependent magnetic measurements (M-H) confirmed the ferromagnetic nature of the prepared sample. M-H loop is not well saturated even at 60 kOe which suggested the presence of anti-site disorder. Multi-domain magnetic structure of the prepared sample suggests its suitability for memory device applications.

Nanostructured Ni0.8Co0.2MnxFe2-xO4 ferrites: Structural, elastic, optical, and electromagnetic properties

Nanostructured Ni0.8Co0.2MnxFe2-xO4 (x = 0.05 and 0.1) ferrites were synthesized via a solution combustion method in a citric acid matrix. The structure, elastic, optical, electrical, dielectric, and magnetic characteristics of these ferrites were analyzed by x-ray diffraction (XRD), Furrier transform infrared (FTIR) spectroscopy, ultraviolent visible (UV–vis) spectroscopy, impedance spectroscopy (IS), and vibrational sampling magnetometer (VSM) techniques. The lattice parameter, crystallite size, hopping length, bond length, cation distribution, elastic parameters, and many others of the ferrites were evaluated using XRD and FTIR data. Well-crystallized single-phase cubic spinel-structured ferrites with the composition of Ni0.8Co0.2MnxFe2-xO4 were produced. The mechanical stability conditions of both ferrites were revealed by the study of their elastic properties. Both ferrites displayed optical activity across the ultraviolet and visible regions, spanning from 300 to 550 nm. The absorption spectra also exhibited peaks at 440 and 460 nm, and a blue shift was observed when Mn3+ content varied from x = 0.05 to x = 0.1. The electrical conductivity was found to be 1.64 × 10−7 S/cm for x = 0.05 and 1.68 × 10−7 S/cm for x = 0.1, and both ferrites exhibited a polaron hopping conduction behavior. The room temperature VSM measurement revealed the ferromagnetic behavior in both of the tested specimens. Higher values of saturation magnetization (60.3 emu/g) and magnetic number nB (2.53 μB) were observed for x = 0.05 ferrite.

Nature of polaronic hopping conduction mechanism in polycrystalline and nanocrystalline Gd0.5Sr0.5MnO3 compounds

In the present study, we have investigated the structural, electrical and magneto-transport properties of polycrystalline and nanocrystalline Gd0.5Sr0.5MnO3 compounds. The variation of transport properties is modified by tuning the grain size of the material. In the high temperature semiconducting region, temperature dependent resistivity data can be well explained by non-adiabatic small polaron hopping (SPH) mechanism. In addition, the resistivity data for all compounds in the low-temperature paramagnetic region can also be well explained by the variable range hopping (VRH) model. The parameters obtained from SPH and VRH mechanisms are found to be reasonable. In the case of nanocrystalline compounds, there is an overlapping temperature range where both SPH and VRH models are valid simultaneously, and a new conduction mechanism - variable range hopping of small polaron s(VR-SPH) is satisfactorily valid for the whole temperature range of these compounds. However, for the polycrystalline compound, the overlapping temperature region between VRH and SPH models does not exist and the VR-SPH mechanism is not valid here. Thus, polarons play a leading role in selecting different conduction mechanisms in different temperature ranges.

Effect of Fe supplantation on structural and dielectric properties of La2CoMnO6

Double Perovskite system La2Co1-xFexMnO6 (x = 0, 0.2, 0.5, 0.8 and 1.0) has been synthesized by sol-gel route. XRD profiles confirmed the absence of any external phase in pure La2CoMnO6 phase. Rietveld refinement analysis confirmed the existence of monoclinic (ordered) as well as rhombohedral and orthorhombic (disordered) structures. Lattice parameters and unit cell volume are found to increase with increase in Fe content. Morphological and compositional analysis was done using FESEM with EDS. Frequency and temperature dependent dielectric characterization revealed the dispersion of both dielectric constant as well as loss tangent at low frequency and high temperature. The Nyquist plot of impedance (cole-cole) revealed negative temperature coefficient of resistance (NTCR) behavior of prepared samples and suggest a non-Debye type relaxation in these samples. An increasing trend with increase in frequency and temperature was exhibited by ac conductivity. Variation of dc electrical conductivity with temperature suggested a semiconducting behavior which can be explained by both small polaron hopping (SPH) and variable range hopping (VRH) conduction mechanisms.

Experimental observation of spin-phonon coupling in Cr2O3 and Fe2O3 solid solution and bandgap engineering

In this work, we present experimental evidence of spin-phonon coupling at room temperature in the solid solutions of Cr2O3 and Fe2O3. The bulk ceramics of Cr2-xFexO3 were fabricated by sol–gel method. The corundum crystal structure with R-3c space group confirmed by Reitveld refinement. Spin-flop transitions observed in the 100–400 K temperature ranges from M−H studies were observed in the lower doping range. The magnetic transition observed from the temperature dependent magnetic studies showed the transition is consistent with the previous reports. The spin-phonon coupling in the ceramics is observed from the two phonon modes in the materials originating from Eg and A1g modes in the Raman spectroscopy. Eg mode shifts towards lower frequency, while A1g mode shifts towards high frequency. UV–vis spectral studies revealed the narrowing of bandgap originating from the Cr-O-Fe hybridisation. Impedance spectroscopy analysis shows that relaxation peaks shift from 90 K to 240 K towards high temperatures. The activation energy value is 0.32 – 0.21 eV, indicating the polaron hopping conductivity in the bulk ceramics.

Structural, electrical and magnetic properties of orthorhombic GdMn1-xNixO3 (0 ≤ x ≤ 0.1): Influence of Ni doping

GdMn1-xNixO3 (0 ≤ x ≤ 0.1) samples were synthesized by traditional solid state reaction method to understand the role of Ni substitution on structural, microstructural, electrical and magnetic properties. Powder X-ray diffraction data reveals the perovskite type structure with pnma space group for all the prepared samples. Scanning electron micrographs shows combined island and disc like granular structures. Raman spectroscopy reveals enhancement in asymmetric stretching mode due to out of phase MnO6 bending and bending mode due to O2 anti-stretching. The temperature dependent dc electrical resistivity confirms the semiconducting nature of the samples, supported by small polaron hopping (SPH) and variable range hopping (VRH) conduction models. The activation energies first increases and then decreases with Ni content. Temperature dependent magnetization under ZFC and FC regimes shows decrement in Tirr with Ni concentration. Currie-Weiss law fittings to inverse of susceptibility data indicates the paramagnetic nature of the samples with presence of antiferromagnetic interactions at 5 K.

Superlinear dependence of the conductivity, double/single Jonscher variations and the contribution of various conduction mechanisms in transport properties of La0.5Ca0.2Ag0.3MnO3 manganite

From the XRD results, it is found that the studied La0.5Ca0.2Ag0.3MnO3 compound crystallizes in the orthorhombic structure with Pnma space group. Electrical conductivity of La0.5Ca0.2Ag0.3MnO3 compound is investigated from 80 K to 480 K in the frequency range [40 Hz-6 × 105 Hz]. Several conduction models are used to identify the appropriate mechanisms governing the transport properties in the studied compound. The Overlapping-Large- Polaron Tunneling and the Correlated Barrier Hopping conduction processes are used to clarify the sub-linear dispersive regions in the DJPL/JPL frequency range. In these regions, the conductivity is examined according to double and single Jonscher power laws. At lower temperatures and for the second frequency range, the spectra reveal Superlinear Power-Law behavior. Beyond T = 280 K, this phenomenon is disappeared and replaced by Nearly Constant Loss behavior. At higher frequencies, the conductivity spectra exhibit a high frequency plateau. For the DC regime, the transport properties are governed by thermally activated Small Polaron Hopping conduction process at elevated temperatures. The Variable Range Hopping conduction mechanism is the dominant process in the intermediate temperature range. Thus, the cationic disorder plays a major role in the transport of charge carriers at low temperatures. Likewise, the investigated compound exhibits semi-conductor behavior over the explored temperature region. The deduced hopping energy is sensitive to the frequency parameter. At high frequencies, a signature of a metal-semiconductor transition is observed at 260 K. The magnetic investigation shows that the sample reveals a paramagnetic-ferromagnetic phase transition at 260 K.

Polaron hopping conduction mechanism and magnetic properties of Pb‐doped LaMnO3

AbstractIn the present work, we have synthesized La1‐xPbxMno3 (0 ≤ x ≤ 0.20) perovskites through a conventional solid‐state reaction route. The powder x‐ray diffraction data analyzed through the Rietveld refinement program confirm monophase rhombohedral distorted structure (R‐3c space group). Fourier transform infrared spectra exhibit strong and well‐defined absorption bands of a typical perovskite structure. The x‐ray photoelectron spectroscopy studies confirm the elemental composition and oxidation state of various elements in the samples. Low temperature resistivity measurements do not reveal metal–semiconductor transition (MST) in the pristine sample while Pb‐doped samples show MST. The metallic region of the temperature‐dependent resistivity data is well fitted with ρ(T) = ρο + ρ2.5T2.5, which reveals the significance of electron–magnon interaction. Moreover, the semiconducting behavior of all the samples follows the Mott's variable range hopping conduction process. Additionally, the semiconducting part is also fitted with the small‐polaron hopping (SPH) model that establishes the non‐adiabatic SPH mechanism obeyed for the lower doping, whereas adiabatic mechanism for the higher Pb concentration. Magnetic studies clearly indicate a paramagnetic to weak ferromagnetic transition associated with the Pb doping that may be due to the double‐exchange mechanism between the manganese ions via oxygen orbitals. The outcomes are elucidated on the basis of substitution effect induced by Pb2+ ions.

Electrical conductivity and temperature sensitivity of Cu/Mo co-modified YFeoO ceramics

To develop a new kind of thermistor with the negative temperature coefficient (NTC) behaviour, the Cu/Mo co-doped YFeO3 based ceramics were prepared by wet-chemical synthesis and sintering at 1300?C. The orthorhombic perovskite structure was identified in all ceramics by XRD analysis. The possible valence states of Fe, Cu and Mo in the doped YFeO3 compounds were examined by X-ray photoelectron spectroscopy. By adjusting the concentration of Cu- and Mo-ions, the room temperature resistivity (?25) and temperature-sensitive constant (B25/85) can be modified from 1.13?103 to 3.09?105 ??cm and 3000 to 7000K, respectively. The complex impedances at various temperatures (from 25 to 150?C) are tested and analysed. The results show that both grain and grain boundary exhibit the NTC characteristics. The electrical conduction mechanisms composing of polaron hopping conduction and band conduction were proposed in the YFeO3 based ceramics.

Synthesis, structural and electrical properties of PVA/TiO2 nanocomposite films with different TiO2 phases prepared by sol–gel technique

Titanium oxide (TiO2) nanoparticles were fabricated by using the sol–gel technique. By controlling the calcination temperature, the different structures of TiO2 (anatase and rutile) have been achieved which is considered a new technique for phase transformation. Moreover, PVA (polyvinyl alcohol)/TiO2 nanocomposite with various TiO2 phases was accomplished by room temperature casting method. The microstructure of TiO2 nanoparticles and its effect on the PVA amorphous phase was confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The functional groups of PVA and TiO2 were inspected by Fourier transform infrared spectroscopy (FT-IR). SEM exhibits an agglomeration nature of TiO2 nanoparticles through the PVA matrix. In this study, the dc conductivity, as well as the transport properties such as activation energy, ions number in unit volume, hopping distance, and polaron's radius were discussed. In the light-temperature of the polaronic hopping conduction models, the electrical conductivity data were examined which is well-described by polaronic models. Besides, it is noted that the nonadiabatic small polaron hopping conduction is realized in this system. The density of state and the decay constant values are acceptable for the localized states.

Frequency dependence of the hopping and disorder energies and conduction mechanisms in Cr-(Pr/Ca) MnO3

Transport properties of Pr0.7Ca0·3Mn0·85Cr0·15O3(Cr-PCMO) manganite have been studied in a large frequency and temperature ranges by mean of impedance spectroscopy. The conductance spectra are discussed in the outline of a double and single Jonscher laws for the temperature ranges [80 K–110 K] and [120–170 K] respectively. The correlated barrier hopping and the non small polaron tunneling (NSPT) conduction models are used to explain the dynamic of charge carriers in the ac regime. The lower temperature range is characterized by the coexistence of such two conduction processes. Below the frequency ν = 105 Hz, the compound exhibits a semiconductor behavior with no detectable electrical transition. A metal - semiconductor transition at around T = 190 K was observed at high frequency range (ν = 2.106 Hz). Beyond the Debye temperature, θD/2 = 130 K, the small polaron hopping (SPH) conduction process is thermally activated. Over the investigated frequency interval ν ≤ 105, the activation of the SPH conduction process needs the same activation energy Ea1 = 112 meV. At lower temperature range, the interaction between electron and acoustic phonon becomes important, the variable range hopping (VRH) mechanism was activated via a disorder energy WD. The temperature dependence of the local energy proves that type of the VRH process is sensitive to the frequency parameter and the investigated temperature range. The hopping and the disorder energies are strongly sensitive to frequency.

Effect of the biphase TiO2 nanoparticles on the dielectric and polaronic transport properties of PVA nanocomposite: Structure analysis and conduction mechanism

Polymeric composite films with tunable electrical and dielectric performance have several uses in electronics based on organic materials. This paper reports the fabrication and the role of TiO2 NPS (nanoparticles) on the dielectric and nanocomposites' conduction of pristine polyvinyl alcohol (PVA). The nanopowder of biphase TiO2 and the nanocomposites of different NPS weight percentages have been fabricated via the sol-gel and casting methods. Structure of the synthesized NPS and nanocomposites were analyzed via PXRD (Powder X-ray diffraction), HR-TEM (High-resolution microscopy of transmission electron), and FTIR (Fourier transform-IR). The average size of the biphase TiO2NPS crystallite is around 52 nm, as calculated from Scherer law. Frequency and temperature dependence of dielectric properties have been studied in a wide range. The dielectric constant of the host matrix has been enhanced by adding TiO2NPS. AC conductivity increases with the further addition of TiO2NPS contents, and its frequency dependence follows the universal power law. The nanocomposite with 6.6 wt% of TiO2NPS shows higher conductivity as compared to other concentrations. The exponent power (s) has values in the range of 0.2–0.9, indicating that the conduction mechanism is correlated with barrier hopping (CBH). The dependence of the DC conductivity on absolute temperature has been studied and obeys Arrhenius relation. Three discrete sections were recognized from the AC conductivity spectra. In light of polaronic hopping conduction models, the electrical conductivity data were analyzed. The analysis shows that the high-temperature conductivity is well explained by the polaronic model, while at an intermediate temperature, the Greaves VRH (variable-range hopping) model is appropriate. Also, the non-adiabatic conduction was established in the nanocomposite system via the application of different suggestions. The values of the decay constant and the density of states confirmed the presence of the localized states. Finally, a small polaron coupling constant (γp) is more significant than four, which indicates a strong electron-phonon interaction.

Room temperature sputtered Cu doped NiO1+δ: p-type conductivity, stability of electrical properties and p-n heterojunction

Abstract Nickel oxide is one of the few wide gap p-type materials which has been applied in many optoelectronic devices. It is well known that the p-type conductivity in NiO arises from Ni vacancy VNi (and/or Oxygen interstitial) acceptors in Oxygen-rich NiO (NiO1+δ). However, due to the instability of these native defects, NiO1+δ is unstable, and its p-type conductivity degrades gradually over time, even at room temperature. In this work, we investigate the effects of copper doping on the optoelectronic properties and the stability of the electrical properties of NiO1+δ (CuxNi1-xO1+δ) synthesized at room temperature by magnetron sputtering. Our results show that with up to 8% Cu doping, the p-type resistivity of NiO1+δ decreases almost by an order of magnitude from 3.3 Ω-cm to 0.4 Ω-cm. Variable temperature Hall measurements show that the hole conduction mechanism can be described by small polaron hopping (SPH) conduction. X-ray photoemission spectroscopy (XPS) confirms that Cu is incorporated as Cu+ acceptors in NiO1+δ. Since the p-type conductivity of CuxNi1-xO1+δ films come from both VNi and the more stable Cu acceptors, the electrical properties of these films are found to be more thermally stable compared to NiO1+δ. P-type CuxNi1-xO1+δ films with x = 0.08 exhibit a reasonable resistivity of ∼30 Ω-cm with a transmittance of 60% after annealing at 400 °C. Furthermore, a p-CuxNi1-xO1+δ and an n-type ZnO p-n heterojunction was fabricated, and the structure shows good rectification. XPS reveals that the p-CuxNi1-xO1+δ/n-ZnO heterojunction has a type-II band alignment with a valence band and conduction band offsets of 1.61 ± 0.1 eV and 1.8 ± 0.1 eV, respectively.

Impact of A-site rare earth substitution on structural, magnetic, optical and transport properties of double perovskites

In the current research work R2CoMnO6 (R = La, Sm, Gd and Dy) double perovskites (DPOs) have been synthesized using auto combustion sol-gel method. Structural characterizations were carried out by X-ray diffraction technique and the analysis confirms the correct crystal structure by Rietveld refinement with a monoclinic symmetry (space group P21/n) in all DPOs. Crystallite size has been calculated by using Scherrer and Williamson-Hall (W-H) methods and found that the crystallite size with the decrease in ionic radius (RLn) decreases from 61.37–49.03 nm on average. The IR reflectivity spectrums fitted by the Lorentz oscillator model reveal that the given DPOs have a monoclinic structure and change of R-site also has ability to impact on the crystal structure. The optical band gap has been estimated in the range of 1.30–1.60 eV reflecting that the considered DPOs have potential to be used as light harvesting materials. The resistivity data of all DPOs depict semiconductor like behavior above room temperature and this behavior has been best described by small polaron hopping (SPH) conduction mechanism. Dielectric measurements exhibit usual dielectric dispersion, which is due to the Maxwell-Wagner-type interfacial polarization in all DPOs. AC conductivity measurement also suggests the conduction is due to SPH.

Nature of correlated polaron hopping mechanism in A-site cation disorder Nd0.7−xLaxSr0.3MnO3 (x = 0.0, 0.1, 0.2 and 0.3) manganites

The structural, transport and magnetic properties of Nd0.7−xLaxSr0.3MnO3 (for x = 0.0, 0.1, 0.2, 0.3) manganite prepared by solid-state route were investigated. All the samples are exhibiting distorted orthorhombic perovskite structure. Lattice parameters and bond angles are increasing with an increase in La concentration. The electrical resistivity ρ(T → 0) and ρ(Tc), both are decreasing with substitution of La (x = 0.0, 0.1, 0.2, 0.3) and the presence of an external magnetic field giving rise to the colossal magnetoresistance (CMR) effect. The temperature-dependent transport nature has been explored with a correlated polaron hopping mechanism based on the Holstein Hamiltonian model. This model is very well concurring with our experimental results and it is further addressing the widely known transition from the low-temperature metallic to the localized polaron hopping conductivity at high temperature. Furthermore, the spin-order temperature (Tc) and the atomic-order temperature (Tca) both are increasing with La substitution. The present analysis shows that the correlated polaron hopping model describes the transport properties of La-substituted Nd0.7−xLaxSr0.3MnO3 samples.

Electrical properties of Nb/Al-doped CuO-based ceramics for NTC thermistors

Nb/Al-modified CuO ceramics (yNb/0.02Al-CuO, 0 ? y ? 0.07, denoted as NACO) were synthesized using sol-gel method for applications in negative temperature coefficient (NTC) thermistors. The phase structure, microstructure and electrical properties of the ceramics were investigated. XRD investigation reveals that the NACO ceramics has the main phase with monoclinic crystalline structure. The analysis of X-ray photoelectron spectroscopy proved the existence of Cu2+/Cu+ and Nb5+/Nb4+ ions. Temperature dependence of the resistivity indicated that the NACO ceramics present typical NTC characteristic. The NTC materials? constant, B value, can be adjusted from 2430K to 3805K by changing the Nb-concentration in the Al-doped CuO ceramics. Among four applied calibration equations the Hoge-3 equation is the most effective one for the resistancetemperature calibration of the prepared NTC thermistors. The complex impedance analysis was performed and revealed that both grain effect and grain boundary effect similarly contribute to the electrical conductive behaviour and NTC feature of the NACO ceramics. The band conduction and polaron hopping conduction are proposed as the conduction mechanisms in the NACO thermistors.

Effect of Yttrium doping on structural, optical and transport properties of La2NiMnO6

We have prepared a series of double perovskites La2−xYxNiMnO6 (x = 0.0, 0.5, 1.0, 1.5, 2.0 mol%) by sol-gel method. The structural, optical and transport properties of La2−xYxNiMnO6 have been characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) and ultra-violet (UV) visible spectroscopy at room temperature whereas dielectric and electrical properties are calibrated in the temperature range of 293–473 K. The structural properties are discussed by rietveld refinement (JANA software) which gives monoclinic structure with space group P21/n for all series. FT-IR measurements give IR spectra which are fitted by using Lorentz oscillator model, optical conductivity, oscillator strength and damping factors. UV-visible spectroscopy gives optical band gaps, indicating the semiconducting behavior of observed series. The transport characteristics of La2−xYxNiMnO6 have been found by dielectric and electrical measurements. The dielectric constant, tangent losses and ac conductivities as function of frequency and temperature have been discussed in detail. The activation energies are calculated by Arrhenius plot which inveterate the semiconducting nature of all samples. It has been further confirmed that there is small polaron hopping (SPH) conduction mechanism in all samples.

Effects of heat treatment on the structural and electrical conductivity of Fe2O3–P2O5–PbO glasses

Glasses having compositions xFe2O3–(80 − x)P2O5–20PbO with x = 20, 25, 30, 35 mol% were prepared by traditional glass melt-quenching method. The effects of the heat treatment of glasses on their structural and electrical conductivity were studied by X-ray diffraction (XRD), differential scanning calorimeter, density (ρ) and dc conductivity (σ). The glass transition temperature (Tg) was observed to increase with Fe2O3 content. The density of the prepared glass and corresponding glass–ceramics increases with Fe2O3 content. XRD of as-quenched glass samples confirm the amorphous nature. Triclinic lead iron phosphate PbFe2(P2O7)2 is the main crystalline ceramic phase formed after heat treatment at 973 K, of 20 and 25 Fe2O3 mol% with average crystallite size of 74 nm. Hexagonal iron phosphate FePO4 phases appeared with Fe2O3 exceeded 30 mol%. The high-temperature conductivity is well explained by polaronic hopping conduction model. It is observed that in this system non-adiabatic hopping conduction is present. The longitudinal optical phonon frequency (νο) and density of state N(EF) of the prepared glass and corresponding glass–ceramics are reasonable for the localized states.