Conduction and dielectric polarization in Se thin films

Se films were prepared by thermal evaporation technique in thickness range 150-8500 Å. X-ray diffraction measurements showed that Se films are in the amorphous state. The ac conductivity and dielectric properties of the amorphous Se films have been investigated in the frequency range 100-100 KHz and 100-400 K temperature range. The ac conductivity σ_ac(ω) is found to be proportional to ω^s where s<1. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier (CBH) model. The dc conductivity at the room temperature was also studied in the same thickness range. It was concluded that the same mechanism of carrier motion might be dominant in both ac polarization and dc conduction. This carrier transport mechanism might be electronic.     

Dielectric and impedance spectroscopy studies on sisal fibre-reinforced polyester composite

Frequency and temperature dependence of dielectric constant (ε_r), dielectric loss (tanδ), ac conductivity (σ_ac) and complex impedance spectroscopy studies on cured polyester matrix and sisal fibre-reinforced polyester composites (SFRPC) have been investigated in the frequency range from 180 Hz to 1 MHz and temperature range from room temperature to 200 °C. The experimental results showed that with the incorporation of sisal fibre, the values of ε_r, tanδ and σ_ac are increased. It is also found that the values of ε_r and tanδ for both cured polyester matrix and SFRPC are decreased with increasing frequency, which indicates that the major contribution to the polarization may come from orientation polarization and interfacial polarization. The increasing value of ε_r with increasing temperature at a particular frequency is due to free motion of the dipole molecular chains within the cured polyester matrix and SFRPC at higher temperature.     

Effect of Vanadium Substitution on the Dielectric Properties of Glass Ceramic Bi-2212 Superconductor

Glass ceramic superconductors were prepared by the melt-quenching method. The frequency and temperature dependence of dielectric constant (????), dielectric loss (????) and loss tangent (tan???) of these superconductors were investigated in the frequency range of 10 kHz?C10 MHz and temperature range of 80?C300 K using the capacitance?Cvoltage (C?CV) and conductance-voltage (G/w-V) measurements. Effect of vanadium on bulk properties, dc electrical resistivity (??) and ac electrical conductivity (?? _ac) of these superconductors were also investigated. The experimental results showed that ????,???? and ?? _ac were strongly temperature and frequency dependent. Negative capacitance (NC) phenomenon has been observed and it is believed that the negative capacitance effect is due to polarization effect. The results can be concluded to imply that the interfacial polarization can occur more easily at low frequencies consequently contributing to the deviation of the dielectric properties and ac electrical conductivity of Bi₂Sr₂Ca₁Cu₂O _?? and Bi_1.9V_0.1Sr₂Ca₁Cu₂O _?? superconductors.     

Characterisation of oxidised erbium films deposited on Si(1 0 0) substrates

Thin Er-oxide films were prepared by oxidation of pure Er films grown on glass and Si (p) substrates. The oxide films were characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD), and optical absorption spectroscopy. The XRD analysis of the as-prepared oxide film and the vacuum-annealed film demonstrates the formation of Er₂O₃ phase with about 4.6% of ErO phase, which totally transforms into Er₂O₃ phase under annealing at 600 °C in dry oxygen. Therefore, the phase-structural changes in the prepared Er-oxide films because of the annealing and the long-time storage in vacuum were studied. The constructed Al/Er-oxide/Si MOS devices were characterised by measuring gate-voltage dependence of their capacitance and ac conductance, from which the surface states density (D_it) of insulator/semiconductor interfacial charges and the density of fixed charges in the oxide, were determined, which were within the device-grade range. The ac-electrical conduction and dielectric properties of the of the Er oxide–silicon structure were studied at room temperature. The data of ac conductivity measurements were found to follow the correlated barrier-hopping (CBH) model and the model's parameters were calculated, while the Kramers–Kronig (KK) relations explain the high-frequency dependence of the capacitance.     

Effect of substrate temperature on ac conduction properties of amorphous and polycrystalline GaSe thin films

X-ray diffraction analysis of GaSe thin films used in the present investigation showed that the as-deposited and the one deposited at higher substrate temperature are in amorphous and polycrystalline state, respectively. The alternating current (ac) conduction properties of thermally evaporated films of GaSe were studied ex situ employing symmetric aluminium ohmic electrodes in the frequency range of 120-10⁵ Hz at various temperature regimes. For the film deposited at elevated substrate temperature (573 K) the ac conductivity was found to increase with improvement of its crystalline structure. The ac conductivity (σ_ac) is found to be proportional to (ω^s) where s < 1. The temperature dependence of ac conductivity and the parameter, s, is reasonably well interpreted by the correlated barrier-hopping (CBH) model. The maximum barrier heights W_m calculated from ac conductivity measurements are compared with optical studies of our previous reported work for a-GaSe and poly-GaSe thin films. The distance between the localized centres (R), activation energy (ΔE_σ) and the number of sites per unit energy per unit volume N(E_F) at the Fermi level were evaluated for both a-GaSe and poly-GaSe thin films. Goswami and Goswami model has been invoked to explain the dependence of capacitance on frequency and temperature.     

FTIR and dielectric studies of nickel doped potassium hexa-titanate (K2Ti6O13) fine ceramics

The dielectric and electrical properties such as relative permittivity $(\varepsilon^{\prime } )$ , loss tangent (tanδ), and ac conductivity (σ_ac) have been studied in the temperature range 373–773 K at three different frequencies 100, 200, 400 kHz for doped potassium hexa-titanate (K₂Ti₆O₁₃) samples. It was observed that dielectric constant and loss tangent decreases while ac conductivity increases with the increase in frequency. The temperature dependent relative permittivity showed a phase transition for all samples. Dielectric loss mechanism was observed to include space charge polarization and dipole orientation. Moreover, electron-hopping conduction was observed to be dominant in the low temperature region, whereas intratunnel ionic conduction prevailed at higher temperatures. Fourier transform infrared spectroscopy analysis was also carried out to identify the chemical bonds present in the specimens.     

Magnetodielectric properties of nano-crystalline BaZr0.15Ti0.85O3/La0.67Sr0.33MnO3 thin film heterostructures

The paper discuses synthesis of La_0.67Sr_0.33MnO₃ and BaZr_0.15Ti_0.85O₃ thin film heterostructures using modified Pechini method (citrate gel) and spin coating technique. The XRD spectra are determined for confirmation of the crystal structure and phase formation of thin film composites. The paper presents variation of real and imaginary parts of dielectric constant ε′, ε″ and tan δ as function of frequency between 100 Hz and 1 MHz and applied magnetic field up to 0.6 T. The paper, also discuses the effect of magnetic field on AC conductivity. The observed variation of magnetocapacitance and impedance spectra are analyzed in terms of a possible equivalent circuit model. The present analysis shows that the method of impedance spectra could be used to separate out the possible contributions to the magnetodielectric effect.     

Tensile,dielectric, and thermal properties of epoxy composites filled with silica,mica, and calcium carbonate

The minerals silica, mica, and calcium carbonate (CaCO₃) were used as fillers to produce epoxy thin film composites for capacitor application. The effects of filler loading and type on the morphology, tensile, dielectric, and thermal properties of the epoxy thin film composites were determined. Results showed that epoxy thin films with 20 vol% filler loading showed good dielectric properties, thermal conductivity, and thermal stability. However, the tensile properties of the thin films were reduced as the filler loading was increased due to brittleness. Dielectric constant and dielectric loss of epoxy/inorganic composite films generally increased with increasing mineral filler loading. Meanwhile, the presence of mineral filler improved the thermal stability of the thin film composites. The highest dielectric constant of 5.75 with 20 vol% filler loading at a frequency of 1 MHz was exhibited by the epoxy/CaCO₃ composite, followed by epoxy/mica and epoxy/silica. Therefore, the epoxy/CaCO₃ composite is the most potential candidate for capacitor application. Moreover, precipitated CaCO₃ provided better tensile properties and slightly improved the dielectric properties compared with mineral CaCO₃.     

High dielectric constant in CaCu3Ti4O12 thin film prepared by pulsed laser deposition

We investigate the dielectric properties of c-axis-oriented epitaxial CaCu₃Ti₄O₁₂ thin film prepared by pulsed laser deposition. The dielectric constants are found to be in the order of 10³-10⁴, depending on the mean grain size for the as-deposited thin films. Furthermore, ac conductivity is measured in the frequencies of 0.1-100 kHz and temperatures of 77-350 K. We find that the dissipation is due to hopping polarization of charge carried at high frequencies and is influenced by interfacial effect at low frequencies. Our results of high dielectric constant and its variation with temperature, the low dielectric loss and the stability of the film show that CaCu₃Ti₄O₁₂ thin film may become a good candidate for certain technological applications.     

Preparation and ac electrical characterizations of Cd doped SnO2 nanoparticles

Nanoparticles (NPs) of the Sn_1?xCd_xO₂ (0.0 ≤ x ≤ 0.04) were synthesized through soft chemistry method. These NPs were characterized for structural, morphological and electrical properties by X-ray diffraction, High resolution transmission electron microscopy and dielectric spectroscopy techniques respectively. Structural analysis confirms that all the NPs are having single phase rutile tetragonal structure. The NPs are of spherical shape and average size of these is found to decrease with Cd doping. Dielectric permittivity and AC conductivity of all the NPs were evaluated as a function of frequency and composition at room temperature. The frequency response of ε_r, ε_i, tan δ and σ _ac show that the dispersion is due to the interfacial polarization and these parameters decrease with doping of Cd in the SnO₂ matrix. The possible correlation between observed dielectric properties and size of NPs, and hence disorder in the system are explored.     

Thickness effect on electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanowhiskers prepared by a hybrid sol-gel route

Silicon-based lead zirconate titanate thick films embedded with zinc oxide nanowhiskers (ZnO_w-PZT) were prepared by a hybrid sol-gel route. ZnO_w-PZT films with thickness from 1.5 μm to 4 μm are perovskite structure and have smooth surface without any cracks. As the thickness increases, the remanent polarization and dielectric constant increase, but the coercive field and tetragonality decrease. Compared with PZT films, the ZnO_w-PZT film has the close tetragonality and electrical properties which are different from those of bulk PZT-based ceramic doped with ZnO powder. The thickness dependences of the ferroelectric and dielectric properties are attributed to the relaxation of internal stress.     

The influence of zinc oxide–cerium oxide nanoparticles on the structural characteristics and electrical properties of polyvinyl alcohol films

With the objective to investigate the influence of zinc oxide–cerium oxide (ZnO–Ce₂O₃) nanoparticles on the electrical properties of polyvinyl alcohol (PVA), PVA/ZnO–Ce₂O₃ nanocomposite films were prepared by solution intercalation method with different weight percentage viz., 0.5, 1.0, and 2.0?wt% of ZnO–Ce₂O₃ nanoparticles. The fabricated nanocomposites were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The effect of ZnO–Ce₂O₃ nanoparticles on the dielectric constant (ε′), dielectric loss (ε″), electric modulus (M′ and M″), ac conductivity (σ _ac), and dielectric loss tangent (tan δ) over a range of frequencies at room temperature of PVA nanocomposites have been studied. FT-IR, XRD, and DSC analysis indicates the nature of ZnO–Ce₂O₃ nanoparticles interaction with the PVA matrix. The morphological behavior of the nanocomposites has been performed using scanning electron microscopy (SEM). The dielectric behaviors such as dielectric constant (ε′) and dielectric loss (ε″) increases with increase in nanoparticle concentration, but decreases with increase in frequency. But, the electric modulus (M′) increases with increase in frequency. Dielectric loss tangent (tan δ) decreases with increase in filler content at lower frequency, but at higher frequencies the tan δ increases with increase in nanoparticles content. AC conductivity (σ _ac) of PVA/ZnO–Ce₂O₃ nanocomposites increases with increasing frequency following the universal dielectric response law.     

Frequency dependence of dielectric properties of ex situ MgB<Subscript>2</Subscript> bulks

In this study, frequency dependent electrical properties of ex situ polycrystalline MgB₂ sintered at 650–850?°C were investigated. Dielectric permittivity (ε′, ε″), dielectric loss (tan δ), alternating current (AC) conductivity (σ_ac) as a function of frequency (100 Hz–10 MHz) were measured at room temperature. The X-ray diffraction (XRD) and grain morphology were analysed and correlated to the findings in dielectric properties. Due to weakly coupled grains and presence of high fraction of oxides, positive real dielectric permittivity was measured for the ex situ samples as compared with the negative real dielectric permittivity shown by the in situ MgB₂. Nevertheless, the samples sintered at higher temperature showed improved grain connectivity as reflected by the higher AC conductivity and dielectric loss. The semicircle observed in the complex impedance plots together with the combined spectroscopy plots indicates that the electrical behavior of the ex situ samples is mainly due to the bulk and grain boundary responses as opposed to the sole bulk response of the in situ MgB₂. The modelled equivalent circuit also suggests the presence of insulating grain boundary barrier (due to the oxide phases) next to the conducting bulk in the ex situ samples.     

Optical properties of CeO<Subscript>2</Subscript> thin films

Cerium oxide (CeO₂) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10⁻⁶ Torr. The thickness of CeO₂ films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850 nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature. The crystallite size of CeO₂ films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values.     

Preparation and optical characterization of lanthanum modified lead zirconate titanate thin films on indium-doped tin oxide-coated glass substrate

Lanthanum modified lead zirconate titanate (PLZT) thin films were fabricated on indium-doped tin oxide (ITO)-coated glass substrate by sol-gel method. The structure of the films was characterized with X-ray diffraction and scanning electron microscopy. The optical properties were investigated in the wavelength range of 220-2400 nm. The sample was modelled as a three layer structure on finite substrate, and optical constants of this system were calculated from the transmission and reflection spectra. The calculated dielectric function was fitted with the Drude model in the case of ITO and a sum of Lorentzian oscillators in the case of PLZT films. For PLZT film the anomalous behaviour of imaginary part of dielectric function was observed below the absorption edge. The possible reasons of that behaviour were discussed.     

Effect of pre-deposition annealing on physical properties of CZTSSe thin films deposed by RF-sputtering based on nanoparticles synthesized by solvothermal technique

This work aims to highlight the beneficial effect of annealing of Cu₂ZnSn(S,Se)₄ (CZTSSe) nanoparticles (NPs) on the properties of the obtained films by RF-magnetron sputtering at room temperature (RT) and at 200 °C. The CZTSSe targets used for the deposition are obtained using nanoparticles synthesized by solvothermal technique. It is denoted that the elemental composition of thin films becomes independent of the growth temperature in the case of annealed CZTSSe NPs. The optical investigation gives that the gap energy is ranging between 1.26 and 1.40 eV with an Urbach’s energy between 100 and 200 meV. By using the Wemple and Didominico model to analyze the refractive index spectra, we have identified common oscillator energy for all CZTSSe thin films and dispersion energy ranging from 2.63 to 5.81 eV. CZTSSe thin films obtained by means of annealed NPs exhibit higher dielectric constant and refractive index. The dispersion of different parameters with experimental conditions is analyzed via a common relationship that illustrates the linear dependence of n₀, E_d, ε_s, and ε_L on the square of the valence difference (ΔZ). The conductivity spectra are deduced, and a theoretical model was identified to fit the permittivity spectra. The obtained results are promising for solar cell applications.

     

Optical properties of HfO2 thin films deposited by magnetron sputtering: From the visible to the far-infrared

Hafnium oxide (HfO₂ or hafnia) holds promise as a high-index dielectric in optical devices and thermal barrier coatings, because of its transparency over a broad spectrum (from the ultraviolet to the mid-infrared) and chemical and thermal stability at high temperatures. In the present work, thin hafnia films of thicknesses from about 180 to 500 nm are deposited on Si substrates using reactive magnetron sputtering. The crystalline structure and surface topography are characterized by X-ray diffraction and atomic force microscopy, respectively. The optical and radiative properties of the film-substrate composites are measured at room temperature using spectroellipsometry and Fourier-transform infrared spectrometry. The optical constants are obtained from about 0.37 to 500 μm by fitting suitable models to the experimental results. Optical properties and dielectric function modeling are discussed with correlation to both film thickness and surface roughness. It is found that a single-oscillator dielectric-function model can describe radiative properties from about 1 to 20 μm. By combining Cauchy's formula (for the visible and near-infrared regions) with a multiple-oscillator Lorentz model (for the far-infrared region), a dielectric function is obtained for the HfO₂ films that is applicable from the visible to the far-infrared.     

Enhanced Dielectric Performance in Polymer Composite Films with Carbon Nanotube‐Reduced Graphene Oxide Hybrid Filler

The electrical conductivity and the specific surface area of conductive fillers in conductor‐insulator composite films can drastically improve the dielectric performance of those films through changing their polarization density by interfacial polarization. We have made a polymer composite film with a hybrid conductive filler material made of carbon nanotubes grown onto reduced graphene oxide platelets (rG‐O/CNT). We report the effect of the rG‐O/CNT hybrid filler on the dielectric performance of the composite film. The composite film had a dielectric constant of 32 with a dielectric loss of 0.051 at 0.062 wt% rG‐O/CNT filler and 100 Hz, while the neat polymer film gave a dielectric constant of 15 with a dielectric loss of 0.036. This is attributed to the increased electrical conductivity and specific surface area of the rG‐O/CNT hybrid filler, which results in an increase in interfacial polarization density between the hybrid filler and the polymer.     

Crystal structure, morphological, optical and electrical investigations of Oxypeucedanin micro crystals: an isolated compound from a plant

The structural, optical and dielectric properties of micro-crystals of Oxypeucedanin (C₁₆H₁₄O₅), isolated from ethyl acetate extract of the roots of the plant Prangos pabularia is presented. These isolated crystals were characterized by using X-ray diffraction (XRD), scanning electron microscopy, optical microscope, ultraviolet (UV)–visible spectroscopy and dielectric spectroscopy techniques. XRD of these crystals confirm that they have monoclinic structure (space group = P2₁/c). The frequency-dependent real part of the complex ac conductivity was found to follow the universal dielectric response: σ_ac (ω)–ω ^s . The trend in the variation of the frequency exponent (s) with frequency (ω) supports the fact that correlated barrier hopping is the dominant charge transport mechanism for this compound. From the UV spectroscopy, the optical band gap (E _g ) has been found to be around 3.76 eV and is following indirect allowed transition. The observed optical and electric properties predict these crystals as an open choice for modern flexible electronics.     

α-Fe2O3 /(PVA + PEG) Nanocomposite films; synthesis,optical, and dielectric characterizations

Hematite (α-Fe₂O₃) nanorods with an average diameter of 40 nm were prepared using a template-free sol–gel method. These nanorods then mixed with polyvinyl alcohol (PVA)/polyethylene glycol (PEG) blend at concentrations of 0.0, 0.5, and 1.0 wt.%. The transmittance percentage (T%) of the films showed a decrease from 80.26 to 33.24 %. The direct optical band gap also decreased from 5.28 to 4.83 eV whereas the refractive index significantly increased with increasing the hematite content. The dielectric measurements were performed in the temperature range 303–413 K and frequency range 30 kHz–3.0 MHz. According to the temperature dependence of the dielectric constant (ε’), α _a -relaxation peaks observed in all films and assigned to the micro-Brownian motion of the polymer blend chains. The behavior of the ac conductivity, σ _ac (f), of the nanocomposite films indicated that the homogenous distribution of α-Fe₂O₃ nanorods allows the formation of conductive three-dimensional networks throughout the nanocomposite film. Also, indicated that the correlated barrier hopping is the most suitable conduction mechanism.