H. Basantakumar Sharma

Fatigue in sol-gel derived barium titanate films

The effect of fatigue on the electrical properties of sol-gel derived ferroelectric barium titanate (BaTiO3) thin films have been investigated. At room temperature, the resistivity, breakdown field, dielectric constant (e), and loss tangent (tan δ) decreases after fatigue while the coercive field increases. Fatigue also influences the dielectric properties of the film at high temperatures. The sharpness and magnitude of the peak in the dielectric constant at the transition temperature decreases after fatigue. The loss tangent of the virgin film showed a peak at the transition temperature while it is absent in the case of the fatigue film. The phenomena are explained in terms of (i) the accumulation of point charge defect, (ii) the pinning of domain wall mobility, and (iii) the space charge layer models of fatigue.

Electrical properties of sol-gel processed barium titanate films

Abstract The sol-gel technique has been used to prepare ferroelectric barium titanate (BaTiO 3 ) films. The electrical properties of the films have been investigated systematically. The room temperature dielectric constant ( ϵ ) and loss tangent (tan δ ) at 1 kHz were respectively found to be 370 and 0.012. Both ϵ and tan δ showed anomaly peaks at 125°C. The room temperature remanant polarization ( P r ) and coercive field ( E c ) were found to be 3.2 μC/cm 2 and 30 kV/cm, respectively. The capacitance–voltage ( C – V ) and conductance–voltage ( G – V ) characteristics also showed hysteresis effect. The temperature variation of C – V and G– V characteristics also confirms the ferroelectric to paraelectric phase transition at 125°C.

On the dipole–dipole correlation and dielectric anisotropy of some N(4-N-alkyloxy benzylidene)4′-N-alkylaniline compounds doped with silver nanoparticles

ABSTRACT Dielectric study of the compounds N(4-n-heptyloxy benzylidene)4′-n-butylaniline and N(4-n-heptyloxy benzylidene)4′-n-hexylaniline at low frequency region (1 kHz–1 MHz) is performed using LCR meter (Agilent 4284 A). A qualitative interpretation in terms of dipole–dipole correlation for both the parallel and the perpendicular components of the dipole moment is given. Further study on the change in the dielectric permittivity and the dielectric anisotropy is made by doping the two compounds separately with dodecanethiol capped silver nanoparticles (0.25% by weight). The molecular positional ordering and relative smectic layer distance influences the change of degree (or type) of dipole–dipole pairing.

Structure and Properties of BT and BST Thin Films

Barium titanate [BT] and barium strontium titanate [BST] solid solution films have been fabricated by a modified sol-gel processing technique from barium acetate {Ba(CH3COOH)2}, strontium acetate [Sr(CH3COOH)2] and titanium (IV) Isopropoxide [Ti[(CH3)2CHO]4] precursors. The as-fired films were found to be amorphous that crystallized to perovskite phase after annealing the films at 550°C in air for one hour. The dielectric constant (ϵ) and loss tangent (tanδ) of the BaTiO3 film at 1 kHz was found to be 360 and 0.01 respectively. The dielectric constant showed a broad anomaly peak at 130°C that confirms ferroelectric-paraelectric transition. The room temperature dielectric constant and loss factor of this film were found to be 450 and 0.005 respectively. The dielectric anomaly peak of the BST film was found to shift towards lower temperature with Sr content. Both BT and BST showed butterfly capacitance-voltage (C-V) and conductance-voltage (G-V) loops, confirming the existence of ferroelectricity in these films.

Influence of Space Charge Layers on the Dielectric Properties of Ba0.6 Sr0.4TiO3 Nanostructured Thin Films

Barium strontium titanate (Ba0.6Sr0.4TiO3) nanostructured thin films have been deposited on platinized silicon substrates by the sol-gel method. The as-fired films were found to be amorphous, which crystallize to cubic phase after annealing at 550°C in air for one hour. The low-frequency dielectric responses of the BST films were measured as functions of frequency range from 1 kHz to 1MHz. The thickness dependence dielectric constant of the BST thin films were measured in the temperature range from −150°C to 150°C at 100 kHz and discussed in the light of an interfacial dead layer. All the samples showed a diffuse type phase transitions. Both the dielectric constant and loss tangent showed anomaly peaks at about 10°C, which corresponds to a tetragonal ferroelectric-to-cubic paraelectric phase transition.

Temperature Dependent Dielectric Properties of Ba0.8Sr0.2TiO3 Nanocrystalline Thin Films

Barium strontium titanate (Ba0.8Sr0.2TiO3) nanocrystalline thin film fabricated by a modified sol‐gel process was crystallized at low temperature 550 °C. The microstructure displayed a polycrystalline nature with average nanograin size of 11 nm. The BST thin film annealed at 550 °C show good dielectric properties. The BST thin films show a diffuse type phase transition. The room temperature dielectric constant and dissipation factors are 310 and 0.03 at 100 kHz, respectively. The capacitance‐frequency curves reveal that the film shows typical frequency dispersion at low frequency. The ferroelectric nature of the BST thin film was indicated by butterfly‐shaped C‐V curves. The effect of temperature on C‐V characteristic of the BST thin films has been investigated. The sample shows paraelectric nature well above the transition temperature as indicated by the absence of butterfly‐shaped C‐V curves.

Dielectric behavior of pure and silver nanoparticle dispersed liquid crystal compounds 7O.4 and 7O.6 under a biasing electric field

ABSTRACT A report on the dielectric response of the liquid crystal compounds - heptyl oxy benzylidene butyl aniline and heptyl oxy benzylidene hexyl aniline – in various smectic and nematic phases under an applied biasing dc electric field is presented. It is found that the orientation of the molecule about the applied dc field is governed by the associated dipole, the structural arrangement of the molecules in different smectic or nematic phase and the ionic motion. Comparative study on pure and silver nanoparticles doped compounds reveal the presence of nanoparticles in the system affecting the local molecular arrangement supporting our earlier findings.

Multiferroic bismuth ferrite thin film and bismuth ferrite-cobalt ferrite nanocomposites

ABSTRACT Bismuth ferrite thin films and bismuth ferrite-cobalt ferrite nanocomposite ceramics were fabricated by a modified sol-gel processing techniques using hydrated bismuth nitrateiron nitrate and manganese nitrate as precursors. As fabricated samples were found to be amorphous that crystalised to desired phases after annealing at 500°C. Thin film samples have high transparencies (∼95.5%). The refractive index of the thin film was found to increases with annealing temperature while the optical band gap shows an opposite trend. The magnetic properties of the ceramic samples were also found to be improved in the nanocomposite samples.

Effect of Mn substitution on structural and dielectric properties of bismuth ferrite

ABSTRACT Bismuth ferrite (BiFeO3 or BFO) and manganese doped bismuth ferrite (BiFe1-xMnxO3, × = 0.1, × = 0.2) ceramic samples were fabricated using sol-gel processing technique. Pure phase BFO powder and its composites were obtained after annealing the as-prepared powder at 500°C. Ceramic samples were then fabricated by pressing in the form of circular discs followed by sintering at 550°C for 2 hours. The influence of Mn doping on structural, morphological and dielectric properties of BiFeO3 were studied and analysed. The frequency responses of dielectric constant (κ) and loss tangent (tanδ) have been investigated over a wide range of frequencies at room temperature.

Optical Properties Of Sol‐Gel Processed BaTiO3/PVDF Nanocomposite Thin Films

Barium titanate/Polyvinylidene fluoride (BaTiO3/PVDF) nanocomposite thin films were fabricated by sol‐gel processing technique. The structural and surface morphological properties have been investigated by using x‐ray diffraction and Atomic force microscopy techniques. The optical properties were investigated by studying the transmittance and absorbance spectra take by UV‐Visible Spectrophotometer. The effect of annealing temperature on the structural and optical properties are reported and analyzed in the light of reported results in the literature.