Electron Hopping Process Research Articles

Polarization loss in rutile TiO2 doped with acceptor ions for microwave absorption

With an increase in electromagnetic (EM) pollution, inducing polarization loss using lattice defects has become one of the main strategies for the design and optimization of a new generation of microwave absorbers. In this study, point defects in TiO2 absorbers are designed and controlled using a sol–gel method. The influences of the electronegativity difference and the ionic valence states of the dopant ions on the microwave absorption (MA) performance of rutile TiO2 composites are investigated. The results show that the defects such as oxygen vacancy (VO∙∙) and Ti3+ can be adjusted continuously at a high-temperature sintering process. Cu2+, which has a larger electronegativity than Ti4+ (Cu2+χ = 1.90 > Ti4+χ = 1.54) promotes the localization of electrons. Furthermore, compared with Ag+, which has a similar electronegativity (Ag+χ = 1.93 ≈ Cu2+χ = 1.90), polyvalent copper ions (Cu2++e→Cu+) enhance the electron-hopping process. The formed electron-pinning defect dipole clusters (TiTi′, VO∙∙, CuTi″, CuTi″′, Ti3+→VO∙∙←Ti3+, Ti3+→VO∙∙←Cu2++e, Cu2++e→Cu+, Ti4++e→Ti3+) produce a stronger polarization relaxation process, which regulates the MA performance of TiO2 absorbers. Therefore, this study provides an essential reference for refining the EM wave attenuation performance of simple oxide absorbers.

Electrical properties of Lithium silicate-based glasses and their Glass-ceramics

Crystallization of lithium di- and meta-silicates were developed in the SiO2–Li2O–TiO2 glass system. Inclusion of TiO2 relatively reduced the crystallization temperature. Through the sintering process at 650 °C/2 h, lithium disilicate was devolved in the TiO2-free sample, whereas the incorporation of TiO2 catalyzed the appearance of lithium metasilicate phases. The microstructure of lithium disilicate glass-ceramics was studied using differential thermal analysis (DTA), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). At 650 °C/2 h, the microstructure consists of spherulitic growths with reasonably sorted nanosize particles in a glassy groundmass. The electrical characteristics of lithium silicate glasses and glass-ceramics having variable concentrations of TiO2 were tested in order to explore their electronic hopping process. To clarify the effects of composition and sintering on the electrical and dielectric behavior of glasses based on lithium silicate, a Broadband Dielectric Spectroscopy (BDS) was employed. While the matching-sintered glass-ceramic exhibits like an insulator with interfacial polarization that significantly lowers the density number of free ions, bulk glass nevertheless demonstrate high conductivity. Lithium oxide considerably increases the conductivity of the composite instead of titanium oxide.

Modelling of transport and recombination of photocarriers in un-doped hydrogenated amorphous silicon (a-Si:H)

In this paper, we report on the simulation of steady state photoconductivity in un-doped a- Si:H at temperatures from 30 to 500 K. The model is based on recombination at dangling bond states and band tail states. It takes also into account the hopping transitions in the conduction hand tail states to describe the conduction in localized states at low temperatures. At high temperatures, the multiple trapping process is considered to describe the conduction in extended states. The density of states includes the exponential density of conduction band tail states and valence band tail slates and the density of dangling bond states. This later is determined by the Defect Pool Model ‘DPM’. The experimental features observed on the temperature dependence of the photoconductivity are generally the thermal quenching, the low activated region and the temperature independent photoconductivity at very low temperatures. All these observations are well reproduced by the model in un-doped a-Si:H. By the examination of the relative contributions of two processes of conduction: (i) the multiple trapping and (ii) the multiple trapping associated with the hopping, the model results show that the multiple trapping process of electrons where the conduction is assured by free carriers in the thermal quenching region above 140 K is important while the hopping process of electrons is negligible. At 140 K and below, the hopping transport of electrons in the conduction band tail states makes an important contribution in the photoconductivity. It explains successfully the low activated region and the temperature independent photoconductivity at very low temperatures.

Multimodal investigation of electronic transport in PTMA and its impact on organic radical battery performance

Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical–radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation.

Ionogel-Electrode for the Study of Protein Tunnel Junctions under Physiologically Relevant Conditions.

The study of charge transport through proteins is essential for understanding complicated electrochemical processes in biological activities while the reasons for the coexistence of tunneling and hopping phenomena in protein junctions still remain unclear. In this work, a flexible and conductive ionogel electrode is synthesized and is used as a top contact to form highly reproducible protein junctions. The junctions of proteins, including human serum albumin, cytochrome C and hemoglobin, show temperature-independent electron tunneling characteristics when the junctions are in solid states while with a different mechanism of temperature-dependent electron hopping when junctions are hydrated under physiologically relevant conditions. It is demonstrated that the solvent reorganization energy plays an important role in the electron-hopping process and experimentally shown that it requires ≈100 meV for electron hopping through one heme group inside a hydrated protein molecule connected between two electrodes.

Spin dynamics of exchange-coupled nitrogen donors in heavily dopedn-type15RSiC monocrystals: Multifrequency EPR and EDMR study

Semiconductor devices based on $15R$ silicon carbide (SiC) show improved properties compared to other polytypes. Here, we report the investigation of nitrogen-doped $15R$ SiC monocrystals with $({N}_{\mathrm{D}}--{N}_{\mathrm{A}})\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ using multifrequency electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) spectroscopic methods in the microwave (MW) frequency range from 9.4 to 328.84 GHz and in the temperature range from 4.2 to 300 K. A single intensive $S$ line with $S=1/2$, at ${g}_{\ensuremath{\perp}}=2.0026(2)$, and ${g}_{\ensuremath{\parallel}}=2.0043(2)$ dominates the EPR spectrum in $15R$ SiC at $T<160$ K and was attributed to the exchange-coupled nitrogen (N) donors substituting quasicubic ``$k1$'' site having the deeper energy level in $15R$ SiC lattice. From the analysis of the temperature behavior of the integral intensity, magnetic field position, intensity, shape, and width of the $S$ line, it was concluded that at $T<90$ K, the exchange coupling occurs between localized donor electrons, while at $T=90\ensuremath{-}150$ K the interaction between exchange-coupled N donors and conduction electrons takes place. In the temperature interval from 20 to 160 K, the $S$-line EPR width was characterized by a two-phonon Orbach relaxation process with the activation energy of $\ensuremath{\sim}6.5$ meV corresponding to the valley-orbit splitting values for N donors in $15R$ SiC. The variable-range hopping regime obeying the ${T}^{1/4}$ law was found to take place at $T<20$ K leading to the appearance of the $S$ line in the EDMR spectrum at low temperatures. The appearance of the EDMR signal from exchange-coupled N donors is caused by the EPR-induced temperature-increase mechanism and the spin-flip hops process. The results obtained from MW conductivity measurements agree with EPR and EDMR data. The temperature variation of MW conductivity was described by several processes, including the electron-hopping process between N donor impurity atoms at $T<50$ K with activation energy ${\ensuremath{\varepsilon}}_{3}=1.5$ meV, electron transitions between Hubbard bands at $T=50--100$ K; the transition of the electrons from the donor energy levels to conduction band with ionization energy ${\ensuremath{\varepsilon}}_{1}=32$ meV at $T=100--200$ K and scattering of the conduction electrons by ionized donors occurred at the temperature higher than 200 K.

Multiferroic property, dielectric response and optical behavior of filled tungsten bronze Ba4Nd2Fe2-xMnxNb8O30 (0 ≤ x ≤ 1) ceramics

In this paper, the structural, magnetic, dielectric, ferroelectric and optical properties of Mn doped tungsten bronze Ba4Nd2Fe2-xMnxNb8O30 (0 ≤ x ≤ 1) ceramics were investigated in detail. All the samples are of single phase with the tetragonal structure and the group space of P4bm. Compared with antiferromagnetism in pure sample, Mn-doped samples show a weak room-temperature ferromagnetic state. The observed ferromagnetism in Mn-doped ceramics can be understood in terms of the AFM coupling of Fe-based and Mn-based sublattices via Dzyaloshinskii-Moriya interaction. The relaxor ferroelectric nature can be demonstrated in the doped samples. The sample x = 0.5 exhibits a high storage energy density U of 1.06 J/cm3 and efficiency η of 94.3%. The low-temperature dielectric relaxation obeys well with Vogel-Fulcher relation and can be ascribed to the local polarization fluctuation, while the dielectric relaxation around 300 K follows with Arrhenius law and can be attributed to the localized hopping process of electrons. In addition, the optical band gap decreases from 2.64 eV to 2.49 eV with increasing the Mn concentration.

Structural, Magnetic, and Electrical Properties and Magnetoresistance of Monovalent K-Substituted La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) Manganite

The effects of K+ substitution at the Ba-site on the structural, magnetic, and electrical properties and magnetoresistance (MR) of La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) manganites prepared via the solid-state method were investigated. Rietveld refinement of X-ray diffraction data confirmed that both samples were crystallized in the rhombohedral structure with the R3c¯ space group. In addition, the unit cell volume, V, and the average grain size also increased with K+ ions. Magnetization versus applied field (M–H) measurement was carried out, and the saturation magnetization (Ms) was found to increase from 1.81 μB/f.u. (x = 0) to 4.11 μB /f.u. (x = 0.04), implying that K+ ions strengthened the ferromagnetic (FM) interaction. Furthermore, the metal–insulator transition temperature, TMI, increased from 257 K (x = 0) to 271 K (x = 0.04). The observed behaviour may be related to the enhancement of double-exchange (DE) interaction due to the increase in Mn-O-Mn bond angle and electronic bandwidth (W), favouring the increasing rate of the eg electron hopping process. The fitting of the electrical resistivity data in the metallic region describes the significance of residual resistivity, electron–electron and electron–magnon scattering processes to elucidate the electronic transport properties. Within the insulating region, variable range hopping (VRH) and small polaron hopping (SPH) models are proposed to describe the conduction mechanism.

Enhanced magnetic properties and magnetodielectric effects in Bi2Fe4O9/BaTiO3 composite

The magnetoelectric properties of Bi2Fe4O9 were improved by compounding with BaTiO3. The magnetic results showed enhanced magnetization in Bi2Fe4O9/BaTiO3 composite compared with Bi2Fe4O9, which originated from the substitution of some Fe atoms in the Ti position of BaTiO3. Bi2Fe4O9/BaTiO3 possessed dielectric relaxation in the temperature range of 120–250 K, which was ascribed to the electron hopping process asymmetrically between Fe2+ and Fe3+. Bi2Fe4O9 and Bi2Fe4O9/BaTiO3 composite both exhibited magnetodielectric effects with an applied magnetic field, indicating magnetoelectric coupling. The maximum coupling coefficient Δε/ε in Bi2Fe4O9/BaTiO3 was approximately − 4.43 % (H = 4000 Oe, f = 0.1 MHz), which was 10 times higher than that of Bi2Fe4O9. The magnetodielectric effects in Bi2Fe4O9 were from the spin-lattice coupling, and the enhanced results in Bi2Fe4O9/BaTiO3 mainly affected by the dielectric relaxation were related to the spin-orbit coupling. In Bi2Fe4O9/BaTiO3, the applied magnetic field altered the energy level of electrons for the Fe2+ (3d6) ion in FeO6 octahedron and then changed the state of electron polarization, which finally gave rise to a change in the dielectric constant. In addition, the stress transfer between the interfaces of Bi2Fe4O9 and BaTiO3 in the composite under a magnetic field also contributed to the magnetodielectric effects.

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

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

Dielectric property of perovskite La0.86Cu3Ti3.42Al0.58O12 ceramic

A novel perovskite La0.86Cu3Ti3.42Al0.58O12 (LCTAO) ceramic was fabricated by a conventional solid-state method, and the dielectric property was systematically investigated. Pure phase with a body-centered cubic structure was confirmed by X-ray diffraction. High dielectric permittivity was performed in wide temperature and frequency ranges. Impedance spectroscopy analysis demonstrated microstructure was electrically heterogeneous, which resulted in a giant dielectric response based on the internal barrier layer capacitor (IBLC) model. The results of X-ray photoelectron spectroscopy indicated the active electron hopping process of the mixed-valence states charge carriers, i.e. Cu+/Cu2+, Ti3+/Ti4+, may be responsible for the semiconduction of grains.

Effects of W/Ni co-doping on the structural, magnetic, electrical, and optical properties of Aurivillius phase Bi5FeTi3O15 ceramics

We investigate the influences of W/Ni co-doping on the structural, magnetic, electrical, and optical properties of four-layered Aurivillius Bi5FeTi3O15 ceramics. All the specimens can be indexed with the orthorhombic structure and the space group of A21am. The incorporation of W/Ni significantly promotes the grain’s growth and compactness. Compared with the antiferromagnetic state in pure sample, a weak room-temperature ferromagnetic state is found in the doped samples. The dielectric relaxations in samples with x ≤ 0.1 follow with Vogel–Fulcher relation and can be ascribed to the fluctuation behavior of local polarization, whereas the dielectric relaxation in sample x = 0.15 obeys well Arrhenius law and is due to the localized hopping process of electrons. The piezoelectric measurements indicate that the composition x = 0.05 represents the largest d33 value of 14pC/N at room temperature, which can be attributed to the optimal conductivity. In addition, all the compositions have two absorption edges with the direct inter-band transition due to the electron excitation from the hybridized Bi 6s + O 2p + Fe t2g valence band to Fe eg and Ti 3d conduction bands.

Wiedemann-Franz Law for Molecular Hopping Transport.

The Wiedemann-Franz (WF) law is a fundamental result in solid-state physics that relates the thermal and electrical conductivity of a metal. It is derived from the predominant transport mechanism in metals: the motion of quasi-free charge-carrying particles. Here, an equivalent WF relationship is developed for molecular systems in which charge carriers are moving not as free particles but instead hop between redox sites. We derive a concise analytical relationship between the electrical and thermal conductivity generated by electron hopping in molecular systems and find that the linear temperature dependence of their ratio as expressed in the standard WF law is replaced by a linear dependence on the nuclear reorganization energy associated with the electron hopping process. The robustness of the molecular WF relation is confirmed by examining the conductance properties of a paradigmatic molecular junction. This result opens a new way to analyze conductivity in molecular systems, with possible applications advancing the design of molecular technologies that derive their function from electrical and/or thermal conductance.

Preparation of Ba2FeNbO6 double perovskite ceramics from molten-salt synthesized powders and their dielectric and magnetic properties

Double perovskite Ba2FeNbO6 (BFN) ceramics were prepared from the molten-salt synthesized BFN powders. The BFN powders have a cubic structure with $$ Fm\bar{3}m $$ space group, confirmed by X-ray diffraction patterns. Their average particle sizes increased with the annealing temperature and dwell time whereas decreased with the molten-salt content. X-ray photoemission spectra revealed both Fe2+ and Fe3+ ions present in the BFN powders and oxygen in the forms of lattice oxygen and oxygen vacancies, while niobium was present as Nb5+. The BFN ceramics exhibited significant frequency-dependent dielectric behavior, and two kinds of dielectric relaxor processes were observed. Their activation energies were 0.16 eV and 0.47 eV, respectively. The electron hopping process (between Fe2+ and Fe3+ ions) with the activation energy of 0.16 eV contributes the low-temperature dielectric relaxation process, and an activation energy of 0.47 eV associated with the high-temperature dielectric relaxation is originally from the barrier energy of the thermal motion of the oxygen vacancies. The dielectric relaxation observed at high-temperature region can be explained by Maxwell–Wagner interfacial polarization in the BFN ceramics. M–H plots of the BFN ceramics at different temperatures revealed their antiferromagnetic nature and a weak ferromagnetic behavior at 2 K. The remanent magnetization (Mr) of the BFN ceramics was measured to be 1.75 emu/g at 2 K and coercive field (Hc) as 1.26 kOe. Magnetization splitting was observed at ~ 290 K between the temperature-dependent magnetizations of the BFN ceramics, which were measured under zero field-cooled (ZFC) and field-cooled modes with an external field of 1 kOe. In the ZFC curve, a maximum peak was observed at 14 K, corresponding to the Neel temperature (TN). The TN of the present BFN ceramics shifts toward low temperature as compared with those prepared by conventional solid-state reaction methods. Such a reduction of the Neel temperature is ascribed to the size effect.

A transition in the electrical conduction mechanism of CuO/CuFe2O4 nanocomposites

The complex impedance, complex permittivity and, alternating current (ac) conductivity investigations of the CuO/CuFe2O4 nanocomposites, prepared by using via co-precipitation and sol-gel methods, were performed between 1 Hz and 40 MHz within 296 K–433 K in the present study. The structural analyses of the samples were determined by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and X-Ray Fluorescence (XRF) techniques. The ac impedance and complex permittivity results revealed that these ferrite systems have a heterogeneous structure consisting of conducting grains surrounded with less conducting grain boundaries which are expressed by Koop’s model. Additionally, the temperature dependent dc conductivity showed up the semiconductor-conductor and conductor-semiconductor transitions in different temperatures. From this point of view, the nanocomposites exhibiting conductive or semiconductor behavior depending on temperature have the potential to be used in many electronic devices, including sensor applications. Moreover, the activation energies of the samples calculated by the Arrhenius plots of the dc conductivity indicated both electron and hole hopping processes for the conduction. Furthermore, small polaron charge transport mechanism was implied by the high activation energies. Ac conductivity analyses of the samples showed that the ferrites prepared in the present work exhibit correlated barrier hopping dominantly for the ac conduction.

Magnetic and electrical transport properties of YbFe2O4

We present magnetic and electrical transport properties such as resistivity, magnetoresistance, dielectric, and polarization of polycrystalline ${\mathrm{YbFe}}_{2}{\mathrm{O}}_{4}$. The ferrimagnetic transition temperature is measured at 243 K, followed by the two low-temperature transitions at $\ensuremath{\sim}190$ and $\ensuremath{\sim}65$ K, respectively. The magnetic properties including the $M\ensuremath{-}H$ hysteresis loops exhibit a strong temperature dependence and possibly indicate a spin-glass state below 65 K for ${\mathrm{YbFe}}_{2}{\mathrm{O}}_{4}$. The iron M\"ossbauer measurement at 295 K confirms the presence of two Fe sites. The measured resistivity can be modeled with the Mott's variable-range hopping model, $\ensuremath{\rho}\ensuremath{\propto}exp{({T}_{0}/T)}^{1/4}$, indicating the electron hopping between ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ sites. The magnetoresistance effects up to 6% at 8 T were observed and the effects could be caused by the field-induced changes in the electron-hopping processes. The frequency-dependent complex dielectric constant has been found to be strongly influenced by the contact effects, and the polarization of polycrystalline ${\mathrm{YbFe}}_{2}{\mathrm{O}}_{4}$ does not show ferroelectricity.

Microstructure and electric response of Li,Sn co-doped NiO ceramics

Phase composition, microstructure and electric response of Li0.05SnxNi0.95 - xO (x = 0, 0.025, 0.05, 0.1) ceramics were systematically investigated. Colossal dielectric permittivity (>5000) is observed in the frequency range of 102-105 Hz at room temperature which becomes highly frequency-independent with increasing temperature. Secondary Sn-rich phase is detected in the grain boundary regions and it has a remarkable influence on the dielectric properties. Impedance spectroscopy analysis demonstrates that the microstructure is electrically heterogeneous, consisting of semiconducting grain and insulating grain boundary. Defect dipoles or polyvalent cations induced at high temperature may activate an electron hopping process under electric field, resulting in the enhancements of grain conductivity and polarization effect. This behaviour should be considered as the origin of the observed dielectric response.

Glasses in the NaPO3-WO3-NaF ternary system: preparation, physical properties and structural studies

Oxyfluoride glasses with composition x WO3 - 30 NaPO3 - (70-x) NaF, with 30 ≤ x ≤ 70 were prepared by melt-quenching and characterized with respect to their bulk physical properties and ionic conductivities. As the NaF content increases, the glass transition temperature, Tg, decreases systematically. Impedance measurements reveal no clear effect of NaF content upon room temperature electrical conductivities and activation energies. There is, however, a significant decrease of the Arrhenius pre-exponential factor with increasing WO3 content, suggesting that the electrical conductivities measured in this glass series are increasingly influenced by an electronic contribution. This contribution may be related to a W5+ → W6+ electron hopping process detected in the optical absorption spectra. Detailed spectroscopic investigations by Raman scattering and multinuclear one- and two-dimensional solid-state NMR experiments indicate that NaF acts like a network modifier resulting in the formation of W-F bonds via breakage of W-O-W and W-O-P linkages, with the former process being the preferred one. The concomitant decrease in network connectivity caused by these processes accounts for the experimentally observed decrease in glass transition temperatures with increasing NaF contents.

Oxygen vacancies induced structural distortions, valence fluctuations and enhanced optical properties in BiFe0.83Ni0.17O3

The present work reports the impact of the oxygen vacancies (OVs) created in multiferroic BiFe0.83Ni0.17O3 in both a qualitative and quantitative manner by employing first principles density functional theory calculations. We have investigated the role of OVs in modulating the structural and optical properties of BiFe0.83Ni0.17O3. Our results have shown that the higher concentration of OVs increases the electron hopping process which ultimately results in the presence of Fe2+ and Fe3+ and the increasing trend of lattice parameters is due to the existence of larger ionic radius Fe2+ in addition to Fe3+ ions. More distortion was realized for the NiO6 octahedron when the OVs were created farther from the Ni ion resulting in changes in the electronic state by decreasing band gaps and providing conductivity. Considerably less distortion was observed when OVs were created nearer to the Ni ion, increasing the band gap values in both up and down spin channels. With respect to optical properties, we conclude that OVs, when created nearer to the Ni ion, increase the absorption behavior in a significant manner. The observed refractive index values are known to be one of the highest values known in the UV-visible range of the spectrum and thus the existence of OVs can drive this material towards applications in optical communication devices. The maximum dielectric constant values of 9–10.5 are observed in all the configurations in the UV and visible region of the electromagnetic spectrum.

Magnetoresistance, magnetic, and dielectric properties of LuFe2O4 prepared by ebeam-assisted solid state reaction

We present structural, magnetoresistance, magnetic, Mössbauer, and dielectric properties of polycrystalline LuFe2O4 prepared by an electron-beam assisted solid state reaction. The x-ray diffraction pattern shows the single phase LuFe2O4 sample, and the ferrimagnetic transition temperature is measured at 240 K, followed by the two low-temperature transitions at 210 K and 140 K, respectively. The magnetic properties including the M-H hysteresis loops exhibit a strong temperature dependence and possibly indicate that LuFe2O4 enters a spin-glass state below 100 K. The iron Mössbauer measurement at 300 K indicates two Fe sites. The resistivity follows Mott’s variable-range hopping model, ρ∝exp(T0/T)1/4, indicating the electron hopping between Fe2+ and Fe3+. The magnetoresistance effects up to 2.5% at 5 T in the ferrimagnetic state were observed, and the effects could be caused by the field-induced changes in the electron hopping processes. The frequency-dependent complex dielectric constant has been found to be strongly influenced by the contact effects, and the intrinsic ferroelectricity of LuFe2O4 could not be ascertained.