N.V. Giridharan

Effect of Dy-substitution on the structural, vibrational, and multiferroic properties of BiFeO3 nanoparticles

Dysprosium (Dy) modified BiFeO3 [Bi1−xDyxFeO3 (x = 0.05, 0.10, and 0.15)] nanoparticles have been synthesized by a low temperature co-precipitation method. Rietveld analysis of X-ray diffraction data reveals a transformation from rhombohedral structure to orthorhombic structure with increase in the Dy concentration. From the transmission electron microscopy analysis, it is observed that the particle sizes of Bi1−xDyxFeO3 (x = 0.05, 0.10, and 0.15) nanoparticles range between 50–70, 40–50, and 30–50 nm, respectively. Raman spectra of Bi1−xDyxFeO3 (x = 0.05) belonging to rhombohedral (R3c) structure show 4A1 and 7E fundamental Raman modes in the range of 100–650 cm−1 and two-phonon scattering modes such as 2A4 (longitudinal optical), 2E8 (transverse optical (TO)), and 2E9 (TO) in the range of 950–1270 cm−1. Suppression, broadening, and shifting of Raman modes have been observed with further increase in Dy concentration. The fundamental Raman modes of Bi1−xDyxFeO3 (x = 0.15) are assigned under orthorhombic (...

Fabrication of ferroelectric (Pb, Ba)TiO3 thin films by sol-gel technique and their characterization

Abstract Ferroelectric (Pb,Ba)TiO 3 (PBT) thin films have been fabricated by sol–gel technique using a barium modified lead titanate sol synthesized from lead acetate tri-hydrate, barium acetate and titanium (iv) butoxide. PBT thin films were deposited on platinum coated silicon and fused quartz substrates by spin coating. The crystal structure and morphology of the films are strongly influenced by the heat treatment performed to form crystalline PBT films. The deposited films possess good compositional homogeneity and thickness uniformity. The dielectric constant and the dissipation factor measured at 1 kHz at room temperature are found to be 118 and 0.015. The remanent polarization and coercive field values are estimated to be 12 μC/cm 2 and 65 kV/cm from the hysteresis studies. The films possess a very low leakage current of ∼10 −7 A/cm 2 as measured from I – V characteristics.

Synthesis and Antifungal Studies on CuO Nanostructures

We report, synthesis and antifungal activities of CuO nanoparticles. Particles are prepared through sol-gel method. X-ray diffraction studies show the particles are monoclinic (crystalline) in nature. Scanning electron microscopic measurements are carried out to understand the morphology of the prepared particles. Energy-dispersive X-ray spectroscopic measurements show that the prepared particles containing Cu and O. To identify the local structure of the particles Fourier transform infra red (FTIR) spectroscopic measurements were carried out showing vibrational bands of Cu-O and O-H band. Anti fungal studies were performed on the set of fungal using disk diffusion method and found that the prepared particles are suitable for antifungal activities.

Synthesis of nanosized BiFeO3 powders by co-precipitation method

A soft chemical co-precipitation method is proposed for the synthesis of nanosized multiferroic BiFeO3 (BFO) powders. Pure phase (BFO) powder was obtained by controlling the chemical co-precipitation process, pH level and calcination temperature. The evolutions of phase constitution and structural characteristics showed that the BFO powders had R3c crystal structure under optimised conditions. Crystallite sizes deduced from X-ray diffraction line width analysis were found to be within 27–31 nm. Fourier transform infrared spectra showed that strong band corresponds to the Fe–O stretching and O–Fe–O bending vibrations. Dielectric and leakage behaviours were also measured at room temperature.

Fabrication and characterisation of (Ba,Sr)TiO3 thin films by sol–gel technique through organic precursor route

Abstract Ferroelectric thin films of barium strontium titanate (BST) have been deposited on silicon and quartz substrates by sol–gel technique through organic precursor route. Crystalline films were obtained by post deposition annealing at a temperature of 700°C. X-ray diffraction (XRD) studies have been carried out to assess the crystallinity and phase formation. The surface features of the films, studied by optical microscopy reveal the grain growth pattern. The refractive index of the film has been estimated. Electrical characterisation of the films such as resistivity and C–V measurements in metal–ferroelectric–semiconductor (MFS) configuration have been carried out. The hysteresis behavior observed during the C–V measurements confirms the ferroelectric property of the films.

Structural, Morphological and Electrical Studies on Barium Strontium Titanate Thin Films Prepared by Sol-Gel Technique

The crystal structure, surface morphology, compositional homogeneity and electrical properties of barium strontium titanate (BST) thin films are investigated. The films were deposited on bare silicon and platinum coated silicon substrates by spin coating process. The precursor solution with Ba/Sr ratio 70/30 was prepared by sol-gel synthesis using metal alkoxides. The crystalline nature and morphology of the films are found to be strongly influenced by the heating cycle adopted to form the Ba 0.7 Sr 0.3 TiO 3 layer. The elemental composition analysis on the surface and in-depth confirms the stoichiometry of the films. The dielectric constant at 100 kHz and dissipation factor at room temperature is found to be 120 and 0.0236 for the films with 400 nm thickness annealed at 700°C for 2 hrs. The leakage current density of the film is found to be 4x10 -8 A/cm 2 from I-V measurements.

Investigations on Al/BaTiO3/GaN MFS structures

Abstract A metal–insulator–semiconductor (MIS) device structure has been established on GaN by using BaTiO 3 , a ferroelectric material, as an insulating layer. The composition of the deposited ferroelectric layers was studied using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) analysis. Fabricated Al/BaTiO 3 /GaN metal–ferroelectric–semiconductor (MFS) structures have been characterised through capacitance–voltage ( C – V ) measurements. Improved C – V characteristics have been observed in comparison to other traditional oxide insulators. An inversion of GaN MFS structures has been attained just for the applied voltage of 5 V due to the high dielectric constant and large polarisation field of the gate ferroelectric layer. The bias stress measurements indicate a high stability of the ferroelectric material over a period of 10 4 s.

Simple synthesis and spectroscopic studies on cobalt added ZnO nanocrystals

Cobalt doped zinc oxide nanoparticles were prepared through simple wet chemical method. X-ray diffraction studies confirm the prepared particles are in wurtzite structure. Scanning Electron Microscopy studies show the shape and morphology of the particles. To identify the presence of cobalt in ZnO, Energy Dispersive X-ray analysis was done. Optical absorption measurements show the presence of exciton peak at 375 nm. Photoluminescence studies were done with the excitation wavelength of 330 nm, which shows the emission because of exciton recombination and oxygen vacancy.

BaTiO3 as an insulating layer for InP-based metal-insulator-semiconductor structures

Abstract Barium titanate (BaTiO 3 ) films were successfully deposited on InP substrates using sol–gel process. The composition of the film has been analysed using X-ray photoelectron spectroscopy (XPS) and the formation of BaTiO 3 has been confirmed. Capacitance–voltage ( C – V ) measurements were carried out on the fabricated Au/BaTiO 3 /InP MIS structures. The surface state density ( N SS ) values were calculated from the C – V measurements using Termans analysis and the minimum N SS value calculated is 7×10 10 cm −2 eV −1 . Deep-level transient spectroscopic (DLTS) measurements have also been carried out on the fabricated MIS structures to find out the traps at the interface. Only one interface state trap is observed at 0.55 eV for Au/BaTiO 3 /InP MIS structures.

Effect of synthesis conditions on the photocatalytic property of multiferroic BiFeO3 towards the degradation of phenol red

Multiferroic BiFeO3 has been synthesized through hydrothermal route under different reaction conditions. From the basic characterization such as of X-Ray diffraction analysis (XRD), the synthesized Nps were found to having rhombohedral structure with R3c space group. Photodegradation studies of toxic dye phenol red have been investigated under visible light irradiation. Vibrating sample magnetometer (VSM) analysis has been carried out to identify the magnetic properties and recycle ability photocatalysts.