Showing papers by "Ajit Kumar Meikap published in 2019"

Study of electrical transport, dielectric and magnetic properties of NiFe2O4-PVDF nanocomposite film

Abstract: In this study, Nickel ferrite (NiFe2O4) nanoparticle (NFO) and Nickel ferrite - Polyvinylidene fluoride (NFO-PVDF) nanocomposite films have been synthesized by chemical route method. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm the formation of pure phase NFO nanoparticles. The electrical transport and dielectric properties of nanocomposite film have been reported in the frequency range 200 Hz ≤ f ≤ 2 MHz and temperature range 303 ≤ T ≤ 410 K. The activation energy (Ea) and barrier height ( φ b ) are enhanced for NFO-PVDF composite film compare to pure PVDF film. The high value of ideality factor implies that the hopping charge transport mechanism is dominated in the composite film. The AC conductivity also follows correlated barrier hopping (CBH) mechanism. The dielectric permittivity increases with filler (NFO) concentration and temperature. Dielectric permittivity and electric modulus are well fitted with the modified Cole-Cole and KWW function. Non-Debye type of relaxation phenomenon is observed in higher temperature and higher filler concentration. The magnetic measurement of the NFO-PVDF composite depicts the soft ferromagnetic behaviour of the materials. The saturation magnetization and hysteresis loop area are increased in higher filler (NFO) concentration.

Structural and electrical characterizations of hydrothermally grown hydroxyapatite polycrystals: A morphological hierarchy

Abstract: Pure hydroxyapatite (HAp) semiconducting microrods with very low dielectric loss have been synthesized in aqueous media of pH values 6, 8, and 10 by the hydrothermal method. Samples are characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectra analyses. The optical bandgap energies of these samples are found to be within the semiconducting range (∼3–4 eV). FESEM and TEM image analyses reveal the formation of microrods and reduction of the average length of the rods with increasing pH values. A core-shell-like microrod structure has been observed in the sample with pH value 6. The charge carrier follows an adiabatic small polaron hopping mechanism. The dielectric loss values are very small compared to that of other ceramic oxides which is very advantageous for electronic applications. Correlated barrier hopping model is the dominant charge transport mechanism within the samples with maximum barrier heights of 0.25 eV, 0.26 eV, and 0.27 eV for samples with pH values 6, 8, and 10, respectively. Nonideal Debye type relaxation appears within the material when the AC field is applied for temperatures above 100 °C.

Influence on loading terbium manganate on optical, thermal and electrical properties of polyvinyl alcohol nanocomposite films

Abstract: In this article, optical, thermal and electrical properties of different wt% of TbMnO3 (TMO) nanoparticles (NPs) loaded poly(vinyl alcohol) (PVA) films are reported in detail. The films are structurally characterised by X-ray diffraction spectroscopy and field emission scanning electron microscopy (FESEM). Optical parameters such as optical band gap energy $$\left( {{E_g}} \right)$$ , Urbach energy $$\left( {{E_U}} \right)$$ are calculated. Red shift in the absorption band of the nanocomposite films indicates the complex formation between the nanofiller and the matrix. Thermal strength increases in TMO-PVA films than the pure PVA film. A reduction in the glass transition temperature $$\left( {{T_G}} \right)$$ of the nanocomposite films is noticed with the insertion of TMO NPs in the PVA matrix. DC conductivity of the samples is explained by Mott’s variable range hopping model, Greave’s model, small polaron hopping model, non-adiabatic hopping model to explain the conduction mechanism. Modified Cole–Cole model explains the frequency variation of dielectric spectra. The relaxation peak position shifts towards lower frequency region with the inclusion of TMO filler in the PVA matrix indicating the decrease in mobility of the dipolar functional groups in the polymer chain. Modified Kohlrausch–Williams–Watts model is applied to explain the frequency dependent electric modulus spectra. AC conductivity of the films is explained by Jonscher’s power law. Correlated barrier hopping model is applied here. The presence of large current of the films at zero voltage may be due to the presence of ferroelectricity in the nanocomposite systems. Oxygen related defect states exist in the polymeric system which exhibit trapping of the charge carriers.

Effect of neodymium doping on electrical properties and relaxor ferroelectric behavior of YCrO3 nanoparticles

Abstract: In this research paper we have discussed the electrical, relaxor ferroelectric and ferromagnetic properties of Neodymium (Nd) doped YCrO3 nanomaterial prepared by sol-gel method. The characterization of the samples is followed by X-ray diffraction (XRD) and Transmission electron microscope (TEM). Upon Nd doping the conductivity of the YCrO3 enhances and the samples show semiconducting behavior. It is also found that the dc activation energy is decreased with the increasing doping concentration. Dielectric permittivity supports the modified Cole-Cole model with dc conductivity contribution correction. Both the space charge and free charge carrier dependent conductivity values increase with the increase of doping content. The frequency dependent conductivity study suggests the Dyre's free energy barrier model. Diffused relaxation peak has been observed in different doped samples. The diffuseness factor γ increases with increasing Nd doping concentration. Enhanced relaxer ferroelectric behavior has been noticed with the increasing Neodymium doping content in YCrO3.

Electrical transport properties of Ni-doped diamond-like carbon films at and above room temperature

Abstract: The dielectric constant, impedance spectroscopy, ac conductivity, and dc conductivity of Ni-doped diamond-like carbon (DLC) films are reported within a wide temperature and frequency window. The dc conductivity increases with temperature, possessing different activation regions. At higher temperatures, a reversible semiconductor to metal transition is observed in the doped samples. Both the ac and dc conductivities are observed to increase with Ni doping concentration. However, the dc self-bias plays an important role in conductivity. The ac conductivity follows Jonscher's power law. The frequency exponent study shows that the ac conduction is governed by the correlated barrier hopping model. The grain boundary resistance is found to be higher than the grain resistance. According to the electric modulus study, the undoped DLC deviates from the ideal Debye behavior, with the deviation being higher in the high-frequency region. The current-voltage characteristics show a nonlinear hysteresis behavior.

Study of optical and thermal properties of terbium manganate nanoparticles

Abstract: We have studied the optical and thermal properties of terbium manganate (TbMnO3) nanoparticles at room temperature. The sample is successfully synthesized by sol–gel method. An orthorhombic phase of the sample is confirmed from XRD analysis. The Williamson–Hall analysis is done to study the contribution of strain and crystallite size on the peak broadening of the synthesized nanoparticles. Elemental analysis of the sample is evaluated from the EDX profile. TbMnO3 nanoparticles exhibit strong absorption in the UV region. The optical band gap is calculated using the Tauc method from UV–Vis absorption spectroscopic analysis. Urbach energy is found to be 0.28 eV for the existence of band distortion and defects in the material. Thermal behaviour of these nanoparticles is determined by non-isothermal thermogravimetric analysis at inert atmosphere. The effect of different heating rates (10, 12, 15 and 20 K/min) on thermal properties of the sample is also investigated. The kinetic parameters are evaluated using different model-free methods in the analysis of solid-state kinetics for thermal behaviour of TbMnO3 nanoparticles. The Coats–Redfern method is used here to determine the apparent reaction order which is found to be ~ 2.

Electrical transport properties of Tb and Mn codoped bismuth ferrite embedded poly (vinyl alcohol) nanocomposite film

Abstract: Tb and Mn codoped Bismuth Ferrite (BTFMO) nanoparticles of crystallite size 45 nm and 2.0 wt% BTFMO- PVA nanocomposite film are synthesized by sol gel method. From Williamson-Hall analysis, strain is found to be 0.4%. Morphological Study reveals the uniform dispersion of BTFMO nanofillers in the PVA matrix. Modified Cole-Cole model is well-fitted with the experimentally observed temperature dependent dielectric response of the film sample above room temperature. A non-Debye type asymmetric behavior is observed. Relaxation time tends to decrease with increasing temperature. Current-voltage study of the film under ±50 V applied voltage exhibits temperature dependent rectifying nature indicating the formation of back to back Schottky Barrier Diode (SBD) with barrier height 0.94eV.Tb and Mn codoped Bismuth Ferrite (BTFMO) nanoparticles of crystallite size 45 nm and 2.0 wt% BTFMO- PVA nanocomposite film are synthesized by sol gel method. From Williamson-Hall analysis, strain is found to be 0.4%. Morphological Study reveals the uniform dispersion of BTFMO nanofillers in the PVA matrix. Modified Cole-Cole model is well-fitted with the experimentally observed temperature dependent dielectric response of the film sample above room temperature. A non-Debye type asymmetric behavior is observed. Relaxation time tends to decrease with increasing temperature. Current-voltage study of the film under ±50 V applied voltage exhibits temperature dependent rectifying nature indicating the formation of back to back Schottky Barrier Diode (SBD) with barrier height 0.94eV.

Ferric hydroxide thin film based novel electrode for electrochemical detection of fluoride ion (F−) present in water in trace level

Abstract: Present article describes the development of novel electrode for the electrochemical detection of fluoride ion (F-) present in water. The electrode is prepared by growing thin ferric hydroxide thin film on conducting glass substrate through simple and cost effective spin coating technique with 150°C calcined temperature. Electrochemical sensing performances of the developed electrode through cyclic voltammetric and amperometric technique are studied within a three electrode chamber where Ag/AgCl and Pt are used as reference and counter electrodes respectively. The developed iron oxide based working electrode shows distinguishable cyclic voltammetric and amperometric response in presence of different concentration (0.27 to 2.48 mM) of aqueous fluoride solution. Morphology and phase of the electrode material is studied prior the electrochemical sensing to understand the behavior of electrochemical interaction. Based on the observations, a plausible mechanism is also proposed for the electrochemical sensing of fluoride by iron oxide thin film.

Thermal and optical properties of flake-like copper oxide nanostructure

Abstract: The flake-like copper oxide (CuO) nanoparticles have been synthesized by calcination method. The XRD pattern and EDX elemental mapping confirms the formation of CuO nanostructure with average crystallite size 4.8 nm. The weight loss of the synthesized material at 800 °C is only 8%. A broad UV-absorption peak arises at 326 nm. A blue shift is observed for the CuO nano-flake. The direct optical band gap value is 2.7 eV and 4.7 eV. A sharp intense peak in the PL spectrum display at 334 nm.The flake-like copper oxide (CuO) nanoparticles have been synthesized by calcination method. The XRD pattern and EDX elemental mapping confirms the formation of CuO nanostructure with average crystallite size 4.8 nm. The weight loss of the synthesized material at 800 °C is only 8%. A broad UV-absorption peak arises at 326 nm. A blue shift is observed for the CuO nano-flake. The direct optical band gap value is 2.7 eV and 4.7 eV. A sharp intense peak in the PL spectrum display at 334 nm.

Study of electrical transport and dielectric properties of NiFe2O4 doped PVDF nanocomposite film

Abstract: Nickel ferrite (NFO) Nanoparticles with crystalline size 35 nm & NFO-PVDF nanocomposite films are successfully synthesized by sol-gel method. Observed DC Conductivity is explained by Arrhenius equation. Activation energies of NFO-PVDF are 0.20 eV and 0.04 for higher and lower temperature regions respectively. AC conductivity is explained by correlated barrier hopping (CBH) model. Dielectric constant and dielectric loss indicate rapid enhancement of permittivity of NFO-PVDF nanocomposite with temperature than pure NFO powder.

Disorder dependence zero temperature dephasing scattering rate in disordered Pd100-xAgx alloys

Abstract: A systematic investigation on electron dephasing scattering rate ( τ φ − 1 ) in Pd100-xAgx at low temperature has been reported. The dephasing scattering rate is dominating by electron-phonon scattering and follows the saturation behaviour for the temperature T → 0 K . The nature of zero temperature dephasing scattering rates cannot be explained by the existing mechanisms and it depends strongly on disorder. Both the electron-phonon coupling coefficient ( A e − p h ) and the zero temperature dephasing scattering rates ( τ 0 − 1 ) follow linear behaviour on mean free path ( l e ) . The magnitude of zero temperature dephasing time ( τ 0 ) increases with increasing disorder, may be due to incomplete momentum randomization by small angle scattering which suggests the requirement of long lime to loss the momentum correlation between initial and final state.