T. P. Sinha

Characterizations of sol-gel grown (PbLaLi)(Zr0.60Ti0.40)O3

Polycrystalline samples of Pb0.92(La1−zLiz)0.08(Zr0.60Ti0.40)0.98+0.04zO3 (z=0.0, 0.1, 0.3, 0.5, 0.7) have been prepared using the metal-alkoxide sol-gel technique. Differential thermal analysis and x-ray diffraction studies show that the above materials can be formed in a single-phase perovskite structure at 550 °C. The formation of grain structure, particle size, and their distributions have been studied by scanning electron microscopy and transmission electron microscopy, respectively. Systematic studies of compositional dependence of ferroelectric properties [dielectric constant (e), dielectric loss (tan δ), remanent polarization (Pr), coercive field (Ec), piezoelectric coefficients, and pyroelectric coefficient (pT)] of the compounds have been done. High value of dielectric constant ∼104, remanent polarization (14–24 μC cm−2), pyroelectric coefficient (46–57 nC cm−2 K−1) and small piezoelectric parameters have been observed for all the compounds with z=0.0, 0.1, 0.3, 0.5, and 0.7. The coercive field ...

Phase transition in sol-gel-derived Na-modified PLZT ceramics

Complex compounds of Na-modified PLZT, Pb0.92(La1-zNaz)0.08(Zr0.60Ti0.40)(0.98+0.04z)O3 (z = 0.0, 0.1, 0.3, 0.5 and 0.7 mol%) (PLNZT) were synthesized by the sol-gel technique. Preliminary structural analysis of the materials from room-temperature XRD data shows that the materials are of tetragonal structure. Detailed dielectric studies of these materials as a function of temperature (30-350 °C) at 10 kHz reveal broad maxima at their respective transition temperatures (Tc). The degree of disorder or diffusivity () lies between 1 and 2 for all the compounds studied, indicating that there is disorder in the system. The remanent polarization (Pr) and coercive field (Ec) determined from the P-E hysteresis loops of the compounds were found to be quadratic and linear functions of temperature respectively, suggesting that a second-order phase transition occurs in them. Measurements of pyroelectric and piezoelectric coefficients provided some useful device parameters.

Electronic Structure of Sr2AlNbO6: Dielectric and X-ray Photoemission Spectroscopy Study

The dielectric property and the electronic structure of double perovskite oxide strontium aluminium niobate, Sr2AlNbO6 (SAN), synthesised by a solid state reaction technique are investigated. The Rietveld refinement of the X-ray diffraction data of the sample shows the cubic phase with the Fm3m structure (lattice parameter, a = 7.7789 A). The compound shows significant frequency dispersion in its dielectric properties. The Cole–Cole model is used to study the dielectric relaxation of SAN. The scaling behavior of loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The electronic structure of SAN is studied by the first principles full potential linearized augmented plane wave method. Its valence band consists mainly of the O 2p states hybridised with the Nb 4d states. The calculated density of states is used to compare the valence band X-ray photoemission spectra of the sample.

Active oxygen and their scavengers in rice seeds (Oryza sativa cv. IET 4094) aged under tropical environmental conditions

Electron paramagnetic resonance studies of high vigour (99% viable) and low vigour (38% viable) dry embryos of rice seeds ( Oryza sativa L.) stored in a natural (warm and humid) environment were carried out. Loss in viability due to hot and humid conditions was found to be correlated with a decrease in free radical levels. The free radicals could be carbon-based and derived from quinones. Presence of the active oxygen scavenging enzyme, superoxide dismutase (EC 1.15.1.1) in embryos isolated from dry seeds showed a positive corrrelation with the state of vigour or viability. Anodic peroxidase (EC 1.11.1.7) activity in imbibed seeds also declined with the decline in vigour and viability. It is concluded that the deterioration of cells in the embryonic axis depends on the balance between free radical accumulation and the activity of active oxygen-scavenging enzymes which constitutes the active oxygen scavenging system (AOSS) during early imbibition. During prolonged storage under hot and humid conditions, cumulative effects of macromolecular damage due to oxidative chain products, compounded with the loss of enzyme activity, result in the final catastrophe, the death of the embryo.

Preparation, characterization and dielectric behaviour of some yttrium doped strontium stannates

Samples of Sr(1− 3x/2)YxSnO3 are prepared by usual solid state reaction route. X- ray diffraction studies confirm the formation of single cubic perovskite single phase. The dielectric constant and dielectric loss at 1 kHz were measured in the temperature range from room temperature up to -150†C. The dielectric constant decreases and losses increase with increased yttrium content in the samples. The percentage porosity and unit cell parameters are also calculated for the samples.

Microstructure and electrical characterisations of K-modified PLZT

Potassium-modified PLZT [Pb0.92(La1 − zKz)0.08(Zr0.60Ti0.40)0.98 + 0.04zO3 (z = 0.0, 0.1, 0.3, 0.5, 0.7)] ceramics were synthesised using sol-gel technique. Preliminary structural and microstructural parameters were determined using XRD, SEM and TEM techniques. Detailed studies of dielectric properties at 10 kHz in a wide temperature range suggest that the compounds have diffuse phase transition of second order. Studies of spontaneous polarisation, pyroelectric and piezoelectric properties yielded data for devices.

Optical properties of perovskite alkaline-earth titanates: a formulation

In this communication we suggest a formulation of the optical conductivity as a convolution of an energy-resolved joint density of states and an energy-frequency labelled transition rate. Our final aim is to develop a scheme based on the augmented space recursion for random systems. In order to gain confidence in our formulation, we apply the formulation to three alkaline-earth titanates, CaTiO3, SrTiO3 and BaTiO3, and compare our results with available data on optical properties of these systems.

An Investigation of the Behavior of Binary Mixed Langmuir Monolayer of 2,2′-p-Phenylenebis (5-phenyloxazol) and Arachidic Acid

A systematic study is reported on the monolayer characteristics of 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) mixed with arachidic acid (AA) at the air-water interface, using surface pressure versus area per molecule (π-A) isotherms complemented with absorption spectroscopy as well as scanning electron microscopy. The (π-A) isotherms of POPOP mixed with AA at different mole fractions show a plateau like region at very low surface pressure, which suggests a phase transition corresponding to a reorientation of the POPOP molecules at the air-water interface. The mixing behavior was obtained from surface pressure-area isotherms by using the surface phase rule and excess area criterion. Results show that POPOP is immiscible in AA, leading to the formation of aggregates. These observations are confirmed by ultraviolet-visible absorption spectroscopy and scanning electron microscopy. Absorption spectra of the mixed LB films reveal that I-type of aggregates play their prominent role in the mixed LB films.

Synthesis and Dielectric Studies of Polyaniline‐Polyacrylamide Conducting Polymer Composites

The intrinsically conducting polymer, polyaniline (PANI) has been synthesized by chemical polymerization process with the help of water‐soluble support polymer acrylamide (AAm). The dielectric measurement of PANI‐PAAm was measured in the temperature range from 303–393 K at frequency 10 kHz. The temperature dependent data has been analyzed in the framework of dielectric permittivity, loss tangent and ac conductivity. The weak temperatures dependence of PANI‐PAAm (below 340 K) is seen, which is an interesting property with respect to technological applications of PANI‐PAAm as an electro‐inactive material around room temperature.

Investigation of dielectric properties of La0.33NbO3 ceramics

La0.33NbO3 ceramics was prepared via conventional solid-state reaction method. Structural analysis show the existence of single phase of La0.33NbO3 has been synthesized with an average particle size of 2 µm – 4 µm estimated from FESEM image. Detailed investigation on the dielectric properties and AC conductivity of the La0.33NbO3 ceramics in a wide range of frequency (800 Hz – 5 MHz) and temperatures (30 °C – 300 °C) revealed that these properties are strongly temperature and frequency dependent.