Ashok R. Lamani

Bio: Ashok R. Lamani is an academic researcher from Kuvempu University. The author has contributed to research in topics: Dielectric & Scanning electron microscope. The author has an hindex of 6, co-authored 28 publications receiving 147 citations. Previous affiliations of Ashok R. Lamani include University of Mysore.

Effect of particle size on band gap and DC electrical conductivity of TiO2 nanomaterial

Abstract: Materials reduced to the Nano scale can exhibit different properties compared to what they exhibit on a micro scale, enabling unique applications. When TiO2 is reduced to Nano scale it shows unique properties, of which the electrical aspect is highly important. This paper presents increase in the energy gap and decrease in conductivity with decrease in particle size of pure Nano TiO2 synthesized by hydrolysis and peptization of titanium isopropoxide. Aqueous solution with various pH and peptizing the resultant suspension will form Nano TiO2 at different particle sizes. As the pH of the solution is made acidic reduction in the particle size is observed. And it is confirmed from XRD using Scherer formula and SEM, as prepared samples are studied for UV absorbance, and DC conductivity from room temperature to 400°C. From the tauc plot it was observed, and calculated the energy band gap increases as the particle size decreases and shown TiO2 is direct band gap. From Arrhenius plot clearly we encountered, decrease in the conductivity for the decrease in particle size due to hopping of charge carriers and it is evident that, we can tailor the band gap by varying particle size.

Synthesis and dielectric properties of Cr-substituted CeO 2 nanoparticles

Abstract: Chromium doped ceria nanoparticles have been synthesized by using a novel solution combustion method with chromium nitrate hexahydrate as oxidizers and glycine as a fuel The main objective of the present study is to find the effect of chromium on structural, optical, dielectric properties and ac- conductivity of cerium oxide nanoparticles (CeO2 NPs) The prepared samples were characterized by various physicochemical techniques such as UV–Vis absorption spectra, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDS) analysis The powder XRD patterns confirm the cubic fluorite structure of CeO2 NPs The UV–Vis absorption spectra showed that the doping causes the red shift of absorption peaks The optical band gap of all samples has been measured by Tauc plot, which is found to be decreases with chromium concentration The uniform shaped NPs with the range of ~ 20 nm is observed by FESEM images EDS analysis confirms the expected elemental composition of Ce1−xCrxO2 NPs The dielectric constant ɛ′, dielectric loss factor (tanδ) and AC conductivity of the samples were studied as function of frequency range from 20 Hz to 3 MHz and found to be decreases with increasing the chromium content

Dielectric and magnetic properties of high porous Gd+3 substituted nickel zinc ferrite nanoparticles

Abstract: We report on the synthesis and characterization of Gd+3 substituted Ni-Zn nano ferrites (Ni0.6Zn0.4GdyFe2−yO4; y = 0, 0.1, 0.15, and 0.2) via low-temperature citrate gel auto-combustion method. The structural studies carried out by PXRD revealed a decrease in the lattice constant and crystallite sizes upon Gd+3 substitution with low concentration but increases with further increase in the concentration. We found the porosity of the samples decreases linearly as a function of Gd+3 concentrations. Well defined spherical grains with a higher porosity of the samples are confirmed by FESEM analysis. With an increase in the Gd+3 concentrations, the dielectric constant increased up to five folds in the magnitude. The contribution of grain boundary and other factors on the electrical properties was revealed by impedance spectroscopy. The reduced remanence ratios showed in the magnetic hysteresis imply the charge in change in the magnetic properties upon the substitution of Gd+3 in the prepared ferrite.

Influence of particle size on band gap and dielectric properties of TiO2 nanomaterials

Abstract: In this work TiO2 nanomaterial of different particle size were synthesized by varying the pH of the solution by hydrolysis and peptization method. These samples were characterized by XRD, UV and SEM. The XRD reveals the formation of anatase phase form of TiO2 nanoparticles having the particle size in the range 15 nm to 35 nm. The calculated band gap values by Tauc plot for the prepared samples increases with decrease in particle size. These samples are pelletized to study the dielectric properties using Impedence Analyzer Interface in the frequency range from 1 Hz to 1 M Hz. From the dielectric studies it was observed that dielectric constant, tanδ and dielectric loss were maximum in lower frequency range, as the frequency increases these dielectric parameters decreases rapidly at low frequency region and almost constant values were recorded at higher frequencies. At lower frequencies, the dielectric parameters (dielectric constant, loss, and tanδ) increases with increase of pH up to pH 8 due to space cha...

Solution Combustion Synthesis: Towards a Sustainable Approach for Metal Oxides.

Abstract: Solution combustion synthesis (SCS) has been widely used to produce simple and complex oxides with a desired morphology (size and shape). SCS is valuable due to low cost, simplicity and energy efficient synthesis. To guarantee the best molecular-level mixing of reactants in an aqueous or solvent-based solution some parameters need to be controlled, such as fuel type, metal cations precursors, stoichiometry ratio (φ), pH effect, atmosphere and initiation type. These determine the final properties of the oxide materials, providing the potential to reach different morphologies, which are essential for their final applications. This Review article focuses on the crucial parameters in SCS and how these affect the overall materials properties from nanostructures to thin films. To finalize, special attention is given to the application of SCS to form metal oxide thin films at low temperature and their application in thin film transistors (TFTs).

Solvothermal synthesis of CoxFe3−xO4 spheres and their microwave absorption properties

Abstract: CoxFe3−xO4 (x = 0–1) spheres are synthesized via a solvothermal reaction using ethylene glycol (EG) as a solvent They are characterized, and the results show that the prepared spheres are mainly 300–500 nm in diameter and constituted by small grains For the EG solution containing stoichiometric ingredients (atomic ratio of Co2+:Fe3+ = 1:2), the obtained spheres are Co09Fe21O4 at 200 °C (sphere A) and Co074Fe226O4 (sphere B) at 300 °C, whose crystallites are 23 nm and 30 nm in size, respectively VSM measurements reveal improved properties with sphere B Variations of complex permittivity and permeability for different composite (75% mass ratio of spheres) have been studied as a function of frequency The calculated reflectivity value indicates that the composite containing sphere A displays better microwave absorption capability The minimum reflection loss reaches −41089 dB at 1208 GHz, with a matching thickness of 2 mm The dielectric loss contributes even more than magnetic loss in the frequency range of 3–14 GHz The synergistic effect of dual losses makes the submicrosphere a promising absorbent in X and Ku bands The composite consisting of sphere B is inferior in dielectric properties owing to ferrous ion migration from octahedral to tetrahedral sites and due to the big crystallites lacking defects After the calcination treatment of the spheres at 700 °C, the dielectric loss turns out to be low due to the disappearing Fe2+ ↔ Fe3+ pairs in adjacent octahedral sites and the loss of defects Variations of the cobalt ratio in spheres can change the resonance frequency and crystallinity of the spheres and ultimately the minimum reflection loss and corresponding frequency band The microwave absorption properties of mixed magnetite and cobalt ferrite spheres are influenced by the cationic stoichiometry and crystalline integrity

Structural, electrical and magnetic properties of (Fe, Co) co-doped SnO2 diluted magnetic semiconductor nanostructures

Abstract: Nanostructures (NSs) of basic composition Sn 1− x Fe x /2 Co x /2 O 2 with x =0.00, 0.04, 0.06, 0.08 and 0.1 were synthesized by citrate-gel route and characterized to understand their structural, electrical and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase rutile type tetragonal structure. The crystallite sizes calculated by using Williamson Hall were found to decrease with increasing doping level. In addition to the fundamental Raman peaks of rutile SnO 2 , the other three weak Raman peaks at about 505, 537 and 688 cm −1 were also observed. Field emission scanning electron microscopy studies showed the emergence of structural transformation. Electric properties such as dc electrical resistivity as a function of temperature and ac conductivity as a function of frequency were also studied. The variation of dielectric properties with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general. Hysteresis loops were clearly observed in M–H curves of Fe and Co co-doped SnO 2 NSs. However, pure SnO 2 nanoparticles (NPs) showed paramagnetic behaviour which vanished at higher values of magnetic field. The grain and grain boundary contribution in the conduction process is estimated through complex impedance plot fitted with non-linear least square (NLLS) approach which shows that the role of grain boundaries increases rapidly as compared to the grain volume with the increase of Fe and Co ions in to system.