S. Panigrahi

Optical and dielectric relaxor behaviour of Ba(Zr0.25Ti0.75)O3 ceramic explained by means of distorted clusters

In this work, Ba(Zr0.25Ti0.75)O3 ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie–Weiss law. The optical properties were analysed by ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV–vis spectrum indicated that the Ba(Zr0.25Ti0.75)O3 ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO6] distorted clusters into a globally cubic matrix. (Some figures in this article are in colour only in the electronic version)

An approach for correlating the structural and electrical properties of Zr4+-modified SrBi4Ti4O15/SBT ceramic

In the present work, B-site modified layer-structured strontium bismuth titanate (SBT) ceramics with the nominal formula SrBi4Ti4−xZrxO15 were prepared by solid state reaction route and the tailoring effects of zirconium (Zr) were investigated thoroughly. The X-ray diffraction analysis shows that the substitution leads to the formation of a single phase layered perovskite up to x ≤ 0.15 and a ZrO2-based secondary phase was detected for higher Zr-doped compositions. The higher grain-growth rate induced by the larger ionic radius of Zr4+ than Ti4+ was supported by the field emission scanning electron microscopy (FESEM) results. The transition temperature increases slightly for the Zr-modified compositions, which can be described in terms of structural distortion due to the internal stresses developed within the ceramics. The Cole–Cole plot analysis of impedance spectra enabled to distinguish two relaxation behaviours that were assigned to originate from grains and grain boundaries. It was also observed that the remnant polarization and piezoelectric coefficient increases up to the solubility limit of Zr and then decreases with higher doping content. The temperature dependent piezoelectric coefficient was also studied, and was found to be stable up to the transition temperature in all compositions. All these results were explained on the basis of occupancy of the Zr4+ ion at the B-site and for the higher composition ZrO2 secondary phase. Even the composition x = 0.15 exhibited low conductivity, a moderate dielectric constant and a highly stable d33 value, demonstrating that the ceramic is an excellent material for high-temperature piezoelectric application. The possible reason for the enhancement of the electrical properties in the Zr-modified ceramic was discussed based on the structural analysis, which may be used for designing and/or modifying properties of SBT-related ceramics.

Diffuse phase transition behavior of dysprosium doped barium titanate ceramic

The effect of dysprosium (Dy) doping on the structural and dielectric properties of barium titanate (BaTiO3) ceramic has been studied. Dysprosium-doped barium titanate (BT) with general formula Ba1-xDy2x/3TiO3 (x = 0.0–0.1) is prepared through solid state reaction route. The XRD pattern reports the single phase tetragonal structure up to x = 0.025 with space group of P4mm and a secondary phase is observed for higher concentration of Dy. The Raman study of Ba1-xDy2x/3TiO3 (x = 0.00, 0.01, 0.025) also reveals that the ceramic is showing tetragonal symmetry and with an increase in Dy doping the tetragonal phase is moving toward more symmetric phase i.e. cubic pm3m. The surface morphology of the sintered pellets shows a compact and homogeneous grain distribution with a decrease in grain size as the Dy content increases. The temperature and frequency dependency dielectric study of the ceramic compositions (x = 0.00, 0.01, 0.025) are studied to show the effect of Dy ion on the A site of BaTiO3 perovskite ceramic. The dielectric constant decreases with increase in Dy content. The dielectric diffusivity increases with increase in doping concentration. The P-E hysteresis loop confirms the ferroelectric behavior of the sample with decrease in remanent polarization and increase in coercive field.

Relaxor ferroelectric behavior of “A” site deficient Bismuth doped Barium Titanate ceramic

A site deficient Bi doped BaTiO3 ceramic with general formula Ba1-xBi2x/3TiO3 (x = 0.00, 0.01, 0.025) is prepared by solid state reaction route. The phase formation and structural property of all compositions are studied by X-Ray Diffraction pattern. The pattern reports single phase tetragonal crystal system with space group of P4mm. The XRD study also reveals that bismuth (Bi) replaces “A” site (Ba) of the BaTiO3 pervoskite. The surface morphology of the sintered pellets is studied by scanning electron microscopy which shows a decrease in grain size with an increase in Bi concentration. The temperature and frequency dependent dielectric behaviors of the compositions are studied to show the effect of Bi ion on the “A” (Ba) site of BaTiO3 perovskite. The dielectric constant decreases and transition temperature increases with increase in Bi concentration. Substitution of Bi ion induces diffuse ferroelectric behavior and the degree of diffuseness increases with increase in doping concentration. The ferroelectric behavior is also confirmed by the P-E loop study.

Rietveld analysis, dielectric and impedance behaviour of Mn3+/Fe3+ ion-modified Pb(Zr0·65Ti0·35)O3 perovskite

The polycrystalline samples of Pb(Zr0·65 − xAxTi0·35)O3 (A = Mn/Fe), (x =0·00, 0·05) (PZM/FT) were synthesized by conventional solid-state reaction technique. X-ray diffraction (XRD) pattern was recorded at room temperature and the samples were found in single phase form. All the observed peaks could be indexed to R3c space group with rhombohedral symmetry. XRD pattern has been analysed by employing Rietveld method with the help of FullProf Program. The lattice parameters and unit cell volumes decrease from Mn3 +  to Fe3 +  ion concentrations. The bond lengths and angles have been calculated by using Powder Cell Programme. Microstructural analysis of the surface of the ceramic compound by scanning electron microscopy (SEM) exhibits that there is a significant change in grain size on introduction of Mn3 +  and Fe3 +  ions at the Zr-site of the compound. It is observed that both the substitutions (Mn3 +  and Fe3 + ) at Zr site induce an increase in dielectric constant and a shift in Curie temperature (Tc). From a.c. conductivity analysis, we have estimated the activation energy for both ferroelectric and paraelectric regions. Both the modified samples are obeying Jonscher power law. From Nyquist plots, the activation energy of grain resistance, relaxation time and bulk conductivity are compared. The grain resistance of the material decreases with rise in temperature which indicates a semiconducting behaviour of the material.

Formation of Complex Langmuir and Langmuir-Blodgett Films of DNA with a Dichain Cationic Surfactant

Formation of complex monolayers between a dichain cationic surfactant, namely, dihexadecyldimethylammonium bromide (DHDAB) and deoxyribonucleic acid (DNA) at the air-water interface was first time systematically investigated here. The adsorption of DNA onto DHDAB monolayer was monitored by observing the surface pressure vs. time graph. The polyion-complex monolayers formed in situ through the electrostatic attraction between cationic DHDAB and the phosphate groups of anionic DNA. The organization of the DNA-DHDAB complex at the air-water interface deduced from surface pressure-area (π-A) isotherms was compared with the spectroscopic data in Langmuir-Blodgett films. Study of UV-Vis absorption spectra of pure DNA solution and DNA adsorbed DHDAB complex Langmuir-Blodgett films confirms the successful transfer of the films onto quartz substrates.

Impedance and Electrical Modulus Study of Microwave-Sintered SrBi2Ta2O9 Ceramic

Bismuth layered structure SrBi2Ta2O9 ceramic is prepared by the microwave sintering technique via solid state route at 1100°C for 30 mins. X-ray diffraction analysis is used to analyze the phase purity, which identifies the orthorhombic structure with A21am space group. The fracture surface of the sintered pellet is visualized by scanning electron microscopy. Impedance spectroscopy is used to analyze the sample behavior as a function of frequency and temperature. Impedance and modulus study reveals the temperature-dependent non-Debye type relaxation phenomenon. The Nyquist plot shows a single arc representing the grain effect in the material, and the conductivity increases with increase in temperature. The Nyquist plot is fitted with an equivalent circuit, and the simulated parameters are well agreed with the calculated parameters. Arrhenius plot shows two different activation energies at below and above 300°C which identifies the phase transition of SrBi2Ta2O9 ceramic. The fatigue property is explained by the basis of activation energies, which shows that SBT sintered by microwave technique is more fatigue resistant than conventional sintering.

Adsorption of Chicago Sky Blue on the Langmuir Monolayer and Langmuir-Blodgett Films of Octadecylamine

This paper reports the incorporation of an inhibitor of Human Immunodeficiency Virus (HIV), viz. Chicago Sky Blue (CSB) dye within an insoluble cationic octadecylamine (ODA) Langmuir monolayer. A surface pressure-area isotherm study confirmed the strong interaction between long chain amine and CSB dye. At higher surface pressure, CSB molecules tend to squeeze out from the octadecylamine monolayer. SEM study confirms this observation. Adsorption kinetics shows that the amount of dye adsorbed depends on the concentration of the dye present in the subphase. It was observed that the absorption process mainly occurred due to the electrostatic interaction between the cationic amino group of long chain amine and the sulphonate group of CSB dye. UV-Vis absorption spectroscopic study indicates the formation of aggregates of CSB dye in the mixed (ODA-CSB) LB films.

Structural and dielectric properties of barium-modified SrBi4Ti4O15 ceramics

Barium-modified strontium bismuth titanate ceramics with chemical formula Sr1−xBaxBi4Ti4O15 (x = 0.00, 0.02, 0.06, 0.08 and 0.1) (SBBT) have been prepared by means of solid-state reaction technique and their structural and electrical properties were investigated. X-ray diffraction data confirm that all the compositions show orthorhombic structure without any deleterious phase. Scanning electron micrographs show plate like grain morphology with random orientation of platelets. The temperature-dependent dielectric study shows that the phase transition temperature decreases, but the dielectric constant increases with increase in Ba content. Complex impedance plots show that both grain and grain boundary effect on the resistance mechanisms in all the compositions. The values of the activation energy confirm that the oxygen vacancies play an important role in the conduction. The ac conductivity of SBBT ceramics increases as a function of frequency due to relaxation phenomenon which arises due to mobile charge carriers.

Investigation of Miscibility and Aggregate Formation in the Mixed Langmuir–Blodgett Films of 2-aminoanthracene by Surface Pressure and Spectroscopic Methods

Nonamphiphilic 2-aminoanthracene has been incorporated within the Langmuir monolayer and Langmuir–Blodgett (LB) films when mixed with behenic acid (BA). Miscibility of 2-aminoanthracene and BA at the air—water (A–W) interface has been studied by using surface phase rule and excess area criterion. Our studies reveal that repulsive type interactions exist between the component molecules in mixed monolayer and this may facilitate the formation of aggregates. Spectroscopic as well as morphological studies of mixed LB films of 2-aminoanthracene and BA undoubtedly confirms the formation of aggregates.