Review on nanomaterials: Synthesis and applications

We have prepared LaCrO3 (LCO) and 10% Ir doped LCO samples by the solid state reaction method and studied the electrical modulus and the other dielectric properties of the samples by means of the impedance spectroscopy in the −100 °C to 100 °C range, with steps of 20 °C. It has been clearly observed that the dielectric properties change due to Ir doping. The absolute dielectric constant value of Ir doped LCO has decreased and this reduction was attributed to decreasing Cr6+ ions which may play a vital role in space charge polarization and charge hopping. A plateau region appeared in the temperature-dependent real electrical modulus M′ versus f curves of the pure LCO sample while almost no plateau region is visible in the Ir doped LCO sample. The temperature-dependent imaginary modulus M′′ versus f curves has two peaks at each temperature; one of the peaks is at low frequency and the other at the high frequency region, which shifts through higher frequency region with increasing temperature. This originates from free charge accumulation at the interface with the increase of the temperature. Furthermore, it has been seen that the Ir doped LCO sample has higher impedance and resistance values than the undoped LCO sample at the same frequency and temperature. This phenomenon was attributed to doped Ir ions behaving like a donor in LCO because LCO is a p-type compound. Moreover, the activation energy values of 0.224 eV and 0.208 eV for LCO and of 0.161 eV and 0.265 eV for the Ir doped LCO have been obtained from the slopes of the ρdc vs. (kT)−1 curves, respectively. Also the activation energies were calculated from the slopes of the fmax vs. (kT)−1 curves and the obtained results from low frequency region were in good agreement with ρdc vs. (kT)−1 ones.

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The electrical modulus and other dielectric properties by the impedance spectroscopy of LaCrO3 and LaCr0.90Ir0.10O3 perovskites

Enhanced visible light-driven photocatalytic performance of CdSe nanorods.

Cadmium selenide (CdSe) semiconductor nanorods are prepared in hydrothermal process using hydrazine hydrate (N2H4.H2O) and ammonia (NH3.H2O) as reducing agents. The reaction time is increased to 7 h and the amount of hydrazine hydrate used is also increased to 15 mL which have resulted in diminished stacking faults in the CdSe nanorods prepared. The crystal structure, morphological variations, and size of the prepared CdSe nanorods are examined by XRD analysis. The crystalline size of the CdSe nanorods is 20-30 nm in diameter. HRTEM images reveal the formation of high order CdSe nanorods of the length about 25-40 nm. The bandgap in the CdSe nanoparticles is determined to be 2.17 eV. The peak at 595 nm in photoluminescence (PL) spectrum indicates oxygen vacancy defects in the prepared CdSe sample. The variation of dielectric properties with respect to temperature and frequency of pelletized CdSe is studied. High photocatalytic efficiency (98%) of catalyst/H2O2 is also achieved for decomposition of Rhodamine-B dye. 

Enhanced visible light-driven photocatalytic performance of CdSe nanorods

Impedance spectroscopy as a tool to monitor the adsorption and removal of nitrate ions from aqueous solution using zinc aluminum chloride anionic clay.

Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance ( R ) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.

Structural and AC conductivity study of CdTe nanomaterials

The antiferromagnetic G-type magnetic ordering in Y2AlCrO6 (YAC) has been investigated by electronic band structure calculations. The material is synthesised by a sol–gel technique and the electronic structure calculations are initiated by the experimental lattice parameters, obtained from the Rietveld refinement of the X-ray diffraction data. The Rietveld refinement shows that the room-temperature crystal structure of YAC is monoclinic with the space group P21/n, and contains an ordered array of alternating AlO6 and CrO6 octahedra tilted along the three pseudocubic axes according to the Glazer notation a−a−b+. The Raman spectrum of the sample is observed for P21/n symmetry. The field cooled and zero field cooled measurements of the sample are performed at a magnetic field of 100 Oe in the temperature range from 5 to 300 K. The temperature dependent magnetization shows the anti-ferromagnetic ordering of Cr ions in YAC. The calculated magnetic moment is well matched with the experimental magnetic moment and suggests the 3+ oxidation state of Cr with the canted alignment of its spin. The octahedral co-ordination of Cr3+ ions in YAC is confirmed from the photoluminescence spectrum. The band gap obtained from the diffuse reflectance measurements shows the semiconducting nature of the material. To observe the effect of grains, grain-boundaries and electrodes in the conduction process, the dielectric relaxation of YAC has been investigated using alternating current impedance spectroscopy in the frequency range from 50 Hz to 5 MHz as a function of temperature. An electrical equivalent circuit consisting of the resistance and the constant phase element is used to explain the impedance data. The observed results are used to discuss the effect of substitution of Cr by Al in the parent compound YCrO3.

Electronic structure and transport properties of antiferromagnetic double perovskite Y2AlCrO6

Nanoparticles of cadmium selenide (CdSe) and Fe (5% and 10%) doped CdSe have been synthesized by soft chemical route and found to have cubic structure. The magnetic field dependent magnetization measurement of the doped samples indicates the presence of anti-ferromagnetic order. The temperature dependent magnetization (M-T) measurement under zero field cooled and field cooled conditions has also ruled out the presence of ferromagnetic component in the samples at room temperature as well as low temperature. In order to estimate the anti-ferromagnetic coupling among the doped Fe atoms, an M-T measurement at 500 Oe has been carried out, and the Curie-Weiss temperature θ of the samples has been estimated from the inverse of susceptibility versus temperature plots. The dielectric relaxation peaks are observed in the spectra of imaginary part of dielectric constant. The temperature dependent relaxation time is found to obey the Arrhenius law having activation energy ~ 0.4 eV for Fe doped samples. The frequency dependent conductivity spectra are found to obey the power law.

Magnetic and dielectric study of Fe-doped CdSe nanoparticles

Cobalt (2 %, 5 % and 10 %) doped cadmium selenide (CdSe) nanoparticles have been synthesized by soft chemical route. The XRD pattern shows the cubic structure of the sample. Crystallization temperature of the samples is calculated using differential scanning calorimeter. The average particle size of all the samples is found to be ∼ 25 nm. Field dependent (M-H) and temperature dependent (M-T) magnetization explains the presence of ferromagnetic components in the samples at room temperature and low temperature. In order to estimate the antiferromagnetic coupling among the doped TM atoms, an M-T measurement at 500 Oe has been carried out under zero field cooled (ZFC) and field cooled (FC) conditions and Curie-Weiss temperature θ of the samples has been estimated from 1/χ vs T plots.

Magnetic study of Co-doped CdSe nanoparticles

Nanoparticles of pure and iron (50 %) doped cadmium selenide (CdSe) have been synthesized by soft chemical route. EDAX analysis supports the inclusion of Fe into CdSe nanoparticles. The average particle size of pure and doped CdSe is found to be ∼50 nm from scanning electron microscopy (SEM). Magnetization of the samples are measured under the field cooled (FC) and zero field cooled (ZFC) modes in the temperature range from 5K to 300K applying a magnetic field of 500Oe. Field dependent magnetization (M-H) measurement indicates presence of room temperature (RT) paramagnetism and low temperature (5K) ferromagnetism of the sample.

Sourish Banerjee

Papers

Structural and AC conductivity study of CdTe nanomaterials

Electronic structure and transport properties of antiferromagnetic double perovskite Y2AlCrO6

Magnetic and dielectric study of Fe-doped CdSe nanoparticles

Magnetic study of Co-doped CdSe nanoparticles

Magnetic study of Fe-doped CdSe nanomaterials