Narrow Results

Cadmium Sulphide (CdS) thin films with different thicknesses were prepared by pulsed laser deposition technique using Nd:YAG laser with wavelength 1064 nm. AC electrical conductivity was studied in the frequency range 100–1000 KHz as a function of temperature. AC conductivity increased with increasing the frequency. The values of the activation energy of the AC conduction were calculated for CdS thin films of different thicknesses at various frequencies. The dielectric constant and dielectric loss were investigated as a function of temperature at different frequencies.

Au/n-Si metal-semiconductor (MS) and Au/Bi₄Ti₃O₁₂/n-Si metal-ferroelectric-semiconductor (MFS) structures were fabricated and admittance measurements were held between 5 kHz and 1 MHz at room temperature so that dielectric properties of these structures could be investigated. The ferroelectric interfacial layer Bi₄Ti₃O₁₂ decreased the polarization voltage by providing permanent dipoles at metal/semiconductor interface. Depending on different mechanisms, dispersion behavior was observed in dielectric constant, dielectric loss and loss tangent versus bias voltage plots of both MS and MFS structures. The real and imaginary parts of complex modulus of MFS structure take smaller values than those of MS structure, because permanent dipoles in ferroelectric layer cause a large spontaneous polarization mechanism. While the dispersion in AC conductivity versus frequency plots of MS structure was observed at high frequencies, for MFS structure it was observed at lower frequencies.

In this study, the dielectric response of Potassium (K${}^{+}$)-doped magnesium aluminates nanoparticles (Mg${}_{1-x}$K${}_x$Al₂O₄, x = 0.0, 0.25, 0.5, 0.75, 1.0) have been investigated as a function of frequency (20 Hz to 2 MHz) at room-temperature. Interestingly, the behavior of dielectric constant indicated the ionic or space charge polarization in the low-frequency range and it remains almost constant at high frequency. However, the value of conductivity increases at higher frequencies which is consistent with the previously reported results for the parent compound MgAl₂O₄. Moreover, the Cole–Cole plots represent various relaxation phenomena reflecting the existence of grain (boundaries) resistance effects.

Y-type hexagonal ferrite (CaBaCo₂Ga${}_{0.5}$Fe${}_{11.5}$O${}_{22}$) was synthesized by sol–gel technique. The ferrite–polymer composites (1−x)CaBaCo₂Ga${}_{0.5}$Fe${}_{11.5}$O${}_{22}$+(x)polyaniline (x=0.25, 0.50, 0.75, 1) namely PF1, PF2, PF3 and polyaniline (PANI) were synthesized by in situ polymerization. The synthesized samples were characterized by XRD, SEM, electrical and dielectric measurements, optical and magnetic studies. XRD pattern reveals a broad peak of polyaniline which is an indication of amorphous nature of PANI. Room-temperature resistivity increases from 2.14 × 10¹ $\mathrm{\Omega }\cdot$cm to 2.78 × 10${}^{10}\mathrm{\Omega }\cdot$cm as ferrite content increases due to resistive behavior of the ferrite particles dispersed in the PANI matrix. The value of dielectric constant decreases at fixed frequency with increasing concentration of ferrite filler which is predominantly due to exchange of electrons between Fe${}^{+2}$ and Fe${}^{+3}$ ions that ultimately results in enhancement of electric polarization and conductivity. The optical bandgap increases with increasing amount of ferrite in the composites. The saturation magnetization and remanence increase with the increase of ferrite filler amount in PANI matrix whereas coercivity decreases. The decrease in coercivity and increase in saturation magnetization are related to Brown’s relation. The present nanocomposite samples may be the best candidates for electromagnetic shielding.

For the first of its kind, Cr${}^{3+}$-substituted calcium hexaferrite (CaCr_xFe${}_{12-x}$O${}_{19}$ ($x=1$, 3, 5 and 7)) nanoparticles (NPs) were synthesized via a facile, economical, eco-friendly lemon juice extract mediated green solution combustion method. The samples were calcined followed by characterization. The Bragg reflections confirm the formation of a single phase M-type hexaferrite crystal structure. No other impurity or mixed phases are observed even after the substitution of Cr${}^{3+}$ to the host matrix. Meanwhile, the crystallite size decreases from 29.44 to 19.92nm with an increase in the substitution of Cr${}^{3+}$ ions. The surface morphological analysis shows the presence of agglomerated irregularly shaped NPs. The direct energy band gap estimated using Wood and Tauc’s relation depicts the decrease in energy band gap from 2.98 to 2.74eV with an increase in the substitution of Cr${}^{3+}$ ions. These Cr${}^{3+}$-substituted calcium hexaferrite NPs were predicted to be useful in high-frequency applications based on structural, dielectric, and magnetic studies.

Impedance spectroscopic studies on polycrystalline sintered discs of lanthanum doped Na_1/2(La_xBi_1-x)_1/2TiO₃ ceramics with x = 0, 0.1, 0.15 and 0.2, have been carried out in the temperature region ranging from room temperature to 550°C and in the frequency range of 100 Hz to 1 MHz. Impedance data is presented in frequency explicit plots and Cole–Cole plots. The relaxation behavior of the charge entities in the above samples is studied as a function of temperature. The structural phase transitions present in the samples showed interesting changes with composition frequency and temperature. An attempt is made to correlate the results obtained to the phase transitions present in the samples.

Sr_0.6Na_0.2Nd_0.2Bi₄Ti₄O₁₅ ceramic is prepared by mixed oxide method. Lattice parameters for this ceramic are calculated from the X-ray diffraction data. Dielectric studies as a function of temperature and frequency are done. To understand the process of conduction involved in the material prepared, frequency and temperature dependency of AC conductivity studies are carried out. The two-term power relation is used to characterize the frequency dependence of AC conductivity. The parameters s₁, s₂ (low and high frequency slopes) are calculated from the AC conductivity plots at different temperatures to get more information about the conduction mechanism. Conduction is explained based on hopping mechanism occuring via polarons.

BiFeO₃-Pb(ZrTi)O₃ [i.e., (Bi_1-xPb_x)(Fe_1-xZr_0.6xTi_0.4x)O₃ (x = 0.15, 0.25, 0.40, 0.50)] nanocomposites were synthesized using mechanical activation followed by a solid-state reaction technique. The dielectric parameters (capacitance, dissipation factor D, impedance Z and phase angle Φ) of all the samples were measured in a wide range of frequencies (1 kHz–1 MHz) and temperatures (300–630 K) in air atmosphere using an impedance analyzer with low signal amplitude of 500 mV. Electrical properties of the compounds were studied using a complex impedance spectroscopy (CIS) technique. The frequency dependence of electrical data was analyzed in the framework of conductivity and modulus formalisms. AC conductivity spectrum obeys Jonscher's universal power law.

Dielectric properties and electrical conductivity of different concentrations of Poly methylmethacrylate (PMMA)/fullerene C60 composites have been reported at room temperature in the frequency range from 1 kHz to 5 MHz. The frequency dependence of complex permittivity, ε*, and complex electrical modulus, M*, have been measured. Frequency dependence of dielectric constant, follows Cole–Cole dielectric relaxation equations, was investigated diagrammatically. Moreover, equations of Tsangaris et al. have been tested for our case to describe the dielectric behavior of particulate polymeric composite containing fillers which give a satisfactory agreement taking into account the variation of the aspect ratio with the volume fraction of fullerene C60 doped in the PMMA matrix.

The effect of cadmium substitution and sintering temperature on the microstructure and dielectric properties of nano ZnCd_xFe_2-xO₄ ferrites (x=0.0, 0.05, 0.1, 0.2, 0.3 and 0.5) has been investigated and prepared by egg-white technique. Electrical conductivity and dielectric measurements have been analysed in the frequency range from 100 Hz to 10 MHz. The variation of the real (ε′) and imaginary (ε″) part of dielectric constant, AC conductivity (σ_AC) and loss tangent (tan δ) with frequency has been studied. It follows the Maxwell–Wagner model based on the interfacial polarization in consonance with the Koop's phenomenological theory. It is found that the permittivity of ZnCd_xFe_2-xO₄ ferrites improved and shows a maximum value (~9 × 10³) at 100 Hz for the x=0.1 sample.

We use the time-dependent Ginzburg–Landau to calculate AC fluctuation conductivity in type-II superconductor in 2D model under magnetic field. Thermal fluctuations are assumed to be strong enough to melt the Abrikosov vortex lattice created by the magnetic field into a vibrating vortex liquid and marginalize the effects of the vortex pinning by inhomogeneities. The nonlinear interaction term in dynamics is treated within self-consistent Gaussian approximation. We obtain expressions the complex conductivity and resistivity summing all Landau levels which are applicable essentially to whole liquid phase and are compared to experimental data on high-T_c superconductor Bi₂Sr₂CaCu₂O_8+δ.

Single crystals of copper succinate dihydrate (CSD) with triclinic structure were grown in silica gel medium. The functional groups in the crystal were analyzed by FT-IR Spectroscopy. Atomic Force Microscopy (AFM) revealed the striations on the surface of grown crystals, which were incorporated during its time of growth. Thermal degradation studies have been carried out by Differential Scanning Calorimetry (DSC). Dielectric constant and AC conductivity have been estimated as a function of frequency at different temperatures.

In this paper, AC measurements on lightly doped n-InP were carried out as a function of temperature down to about 16 K and at frequencies in the range from 120 Hz up to 10⁵ Hz. The AC conductivity at low temperatures is of a single hopping nature following the universal law; σ(ω) ~ ω^s, where the exponent, s, is temperature-independent. At relatively high temperatures (but still below the room temperature) the AC conductivity is of a multiple hopping nature.

Lithium cobalt nanoferrites having the compositional formula Li_0.5-x/2Co_xFe_2.5-x/2O₄ with x varying from 0.00 to 0.12 in steps of 0.03 were prepared by the chemical sol–gel method. Samples were heated at two different temperatures namely 300°C and 500°C for 4 h. Structural characterization of the samples was done using X-ray diffraction (XRD) technique and confirmed the formation of single phase with spinel structure in all the samples. From the XRD data, the lattice parameter was calculated and found to range from 82.87–83.35 nm while the crystallite size was found to be in the range 17–34 nm. Microstructural studies were carried out using the Scanning Electron Microscopy and revealed the microstructures with grain size ranging from 35–70 nm. Electrical properties like dielectric constant, dielectric loss and AC conductivity for these nanoferrites were investigated. The frequency variation of room temperature dielectric constant, dielectric loss and AC conductivity were studied in the frequency range 100 Hz–1 MHz, and a dispersive behavior was observed, which has been attributed to the Maxwell–Wagner type of interfacial polarization.

Hexagonal yttrium manganites, YMnO₃, are interesting materials for their multiferroic behavior. Substituting suitable cations either at the Y-site or Mn-site offers great opportunities to produce a variety of manganites and tune their properties. Nanocrystalline yttrium iron manganites with the compositional formula Y${}_{1-x}$Fe${}_x$MnO₃, $x$ = 0.0, 0.10, 0.15, 0.20 and 0.25, were synthesized by sol–gel autocombustion method. The prepared samples were heated at 1100${}^{\circ }$C for 1 h. Another set of samples with compositional formula YFe${}_x$Mn${}_{1-x}$O₃, $x$ = 0.0, 0.10, 0.15, 0.20 and 0.25, were also synthesized by the same method and heated at 1100${}^{\circ }$C for 1 h. Various characterizations were done on these manganite systems synthesized by substituting iron at different sites. X-ray diffraction (XRD) technique studied the structure of the samples and analysis of XRD patterns confirmed the formation of hexagonal phase in the samples. Structural parameters such as lattice constants, crystallite size, theoretical density, etc. were determined using the XRD data. The unit cell dimensions have been found to agree with the standard data and the Debye–Scherrer crystallite size obtained from XRD data ranges from 42 nm to 77 nm. The room temperature frequency variations of electrical properties such as dielectric constant, dielectric loss and AC conductivity were measured in the range of 100 Hz–2 MHz and the variations showed a dispersive behavior for all the samples. The various measurements and the results obtained were studied and discussed in the paper.

In the present manuscript, we have reported the synthesis, structural, optical, AC conductivity and dielectric studies of carbon dot-zinc oxide (CDZO) nanocomplexes. CDZO nanocomplexes were synthesized by the wet chemical method. The refinement of X-ray powder diffraction data reveals that the sample possesses hexagonal structure of ZnO. The low intensity diffraction peaks corresponding to carbon come to existence, it is suggested that phase segregation has occurred in the CDZO nanoparticles. The strong absorption band observed in the UV region for the prepared samples can be attributed to the band edge absorption. Dielectric property and AC conductivity have been studied as a function of frequency (100Hz and 1kHz) of the applied AC signal in the temperature range 30${}^{\circ }$C to 150${}^{\circ }$C. The result showed that AC conductivity increases with increase of temperature. Dielectric loss and DC conductivity increase with increase of temperature.

In this study, ZnO–Fe₂O₃ nanocomposites were prepared by high-energy ball milling technique and characterized through X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), UV–visible spectroscopy and dielectric spectroscopy. The amount of Fe₂O₃ in the ZnO–Fe₂O₃ nanocomposites was varied at the rates of 1wt.%, 3wt.% and 5wt.% in order to investigate its influence on the structural, optical and dielectric properties of the nanocomposites. XRD patterns of nanocomposites revealed no shift in peak positions and hence confirmed the formation of composites after ball milling. Further, it was observed from FESEM analysis that Fe₂O₃ particles were distributed randomly on the ZnO matrix of the nanocomposites. ZnO–Fe₂O₃ nanocomposites reveal extended optical absorption in the range of 400–600nm from UV studies. The dielectric constant and loss of the nanocomposites decrease exponentially with increase in frequency. The composition and frequency dependences of the dielectric constant, dielectric loss and AC conductivity are explained based on the Maxwell–Wagner effect and Koop’s theory.

We present the production and extensive characterization of a polyacrylamide (PAAm)/polyvinyl alcohol (PVA) polymeric blend doped with varying percentages of cadmium sulfide (CdS) nanoparticles (NPs). Using the solution casting method, CdS-filled PVA/PAAm polymeric nanocomposite (PNCs) films in various weight ratios and percentages were created. The SEM pictures confirmed the identical spreading of CdS NPs in the mix. The filler CdS material might be used to modify the optical characteristics. The film’s direct optical energy gap ($E_g$ (dir.)) has been adjusted from 2.30eV to 3.30eV. The intermolecular interactions of the PVA/PAAm mix were investigated using FT-IR analysis. The electrical properties of alternating current were studied throughout a frequency range of 100Hz–5MHz. The impact of CdS NPs on the dielectric coefficient (${\epsilon }^{\prime })$, dielectric loss (${\epsilon }^{\prime \prime })$ and ac conductivity (${\sigma }_{\text{ac}})$ of PVA/PAAm PNCs over a range of frequencies at room temperature has been investigated. With increased CdS NPs, the attenuation coefficient values rose. We demonstrated that doping CdS composites with PVA/PAAm increases the antibacterial (ANB) activity of the composites. As a result of these findings, the PNCs films are appropriate for gamma-ray shielding (GRS) and ANB applications.

The biological use of nanocomposites (NCs) is highly intriguing and is more acknowledged for its value, particularly in nanomedicine. The key goal of this study is to investigate the influence of vanadium nanoparticles (VNPs) addition on PVA’s morphological, optical, and electrical properties. In this work, the PVA/V nanocomposites (NCs) were fabricated with different VNP contents of (0.02, 0.04, and 0.06) wt.% by the casting solution technique. The optical microscopy (OM) and scanning electron microscope (SEM) have been used to examine the surface morphological features of produced films, which showed that the VNP clusters were well dispersed in the polymer medium. The intermolecular interaction of the PVA/V nanocomposite was studied by FTIR examination. The interaction between PVA and V was confirmed by observing the change in IR absorption intensity. The UV–Vis approach was used to explore the optical characteristics of the UV–Vis region. The experimental data demonstrate that variations in the concentration of VNPs significantly impact the absorption. For the doped samples, the absorbance against wavelength is exponential. There is evidence of interface between polymer and nanoparticles because the optical band gap has shrunk from 4.50 eV to 3.30 eV, with a corresponding narrowing of the gap between the valence and conduction bands. The electrical characteristics of alternating current were investigated in the frequency range of 100–5 MHz. The dielectric constant and loss of NC films reduced as the concentration of VNPs rose, whereas electrical conductivity increased. With rising VNPs, the attenuation coefficient values rose. The inhibition zone diameters of Staphylococcus aureus bacteria increased with the increase of VNP contents. We showed that adding polyvinyl alcohol (PVA) to V composites increases their antimicrobial (ANB) activities. Based on these findings, NC films can be used for gamma-ray protection and antimicrobial (ANB) purposes.

Lead free (K_0.5Na_0.5)NbO₃ (KNN) ceramics were prepared by conventional solid state reaction route. For single perovskite phase formation, calcination temperature was optimized at 850°C for 6 h, whereas for dense morphology the sintering of the ceramic was carried out at 1120°C for 4 h. X-ray diffraction XRD analysis confirmed the formation of single phase with orthorhombic structure at room temperature. Impedance analysis and AC conductivity studies of the KNN sample was carried out in the temperature range of 703–773 K. Impedance study showed the increase in conducting behavior at higher temperature. The temperature dependence of AC conductivity indicated that the conduction process is due to doubly ionized oxygen vacancies in the higher temperature region.