Ashok K. Batra

Growth of large methyl-(2,4-dinitrophenyl)-aminopropanoate: 2-methyl-4-nitroaniline crystals for nonlinear optical applications

Abstract Large single crystals (8 × 8 × 80 mm 3 ) of mixed methyl-(2,4-dinitrophenyl)-amino-propanoate(MAP): 2-methyl-4-nitroaniline(MNA) have been grown by a novel solution crystal growth technique. In this technique, the seed crystal is pulled upward from its growth solution at a controlled rate along with a decrease in the solution temperature to create a desired supersaturation. Information about the morphology-solvent relationship of spontaneously nucleated crystals is also given. The grown crystal is of high optical quality with appropriate size for fabrication of optical devices.

Present Status of Polymer : Ceramic Composites for Pyroelectric Infrared Detectors

‘Ferroelectrics:Polymer’ composites can be considered an established substitute to conventional electro-ceramics and to ferroelectric polymers. The composites have unique blend of polymeric properties such as mechanical flexibility, high strength, formability, and low cost with high electro-active properties of ceramic materials. It has attracted considerable interest because of their potential use in pyroelectric infrared detecting devices and piezoelectric transducers. These flexible sensors and transducers may eventually be useful for NASA crew launch vehicles and crew exploration vehicles being developed for their health monitoring applications. In the light of many technologically important applications in this field; it is worthwhile to present an overview of the pyroelectric infrared detector theory, models to predict dielectric behavior and pyroelectric coefficient in conjunction with the concept of connectivity and fabrication techniques of biphasic composites. An elaborate review of ‘Pyroelectric: Polymer’ composite materials investigated to date for their potential use in pyroelectric infrared detectors is presented.

Modified triglycine sulphate (TGS) single crystals for pyroelectric infrared detector applications

Effect of caesium and cerium,l-alanine and caesium +l-alanine impurities are investigated on ferroelectric and pyroelectric properties of TGS crystals. Dielectric constant and loss, pyroelectric coefficient, spontaneous polarization and coercive field measurements of these modified crystals, as a function of temperature are reported. Caesium and cerium did not affect the electrical properties of TGS crystals significantly, whereasl-alanine- and, especially, Cs +l-alanine-doped TGS crystals exhibited promising improvements in pyroelectric properties, up to 48 °C, as compared to pure TGS crystals.

Perovskites: transforming photovoltaics, a mini-review

Abstract. The recent power-packed advent of perovskite solar cells is transforming photovoltaics (PV) with their superior efficiencies, ease of fabrication, and cost. This perovskite solar cell further boasts of many unexplored features that can further enhance its PV properties and lead to it being branded as a successful commercial product. This article provides a detailed insight of the organometal halide based perovskite structure, its unique stoichiometric design, and its underlying principles for PV applications. The compatibility of various PV layers and its fabrication methods is also discussed.

Growth and properties of urea-doped triglycine sulfate (UrTGS) crytals

This paper discusses the growth and properties of triglycine sulfate (TGS) crystals doped with urea. It was found that the normalized growth yield and pyroelectric and dielectric constants could be increased significantly by urea additions. TGS crystals doped with 5 and 10 wt% urea exhibited up to five times higher material figures of merit for infrared pyroelectric detectors compared with undoped TGS crystals. The Vickers hardness of doped crystals increased with urea content to about three times the undoped value in the [010] direction at 10 wt% urea. No significant increase in the hardness was found, however, in the [001] direction. Incorporation of urea in TGS crystals has been qualitatively estimated by Fourier transform infrared (FTIR) data.

Pyroelectric Properties of PVDF:MWCNT Nanocomposite Film for Uncooled Infrared Detectors and Medical Applications

The biocompatible and flexible polyvinylidene fluoride (PVDF) has a number of interesting pyroelectric and piezoelectric properties with fast, dynamic response for use in touch/tactile sensors, infrared detectors and thermal vidicon/imaging devices. Pyroelectric multi-walled carbon nano-tubes:polyvinylidene fluoride nano-composite films were fabricated via the solution casting technique. The dielectric, pyroelectric and piezoelectric characteristics of composite films were measured. Using foregoing parameters, figures-of-merit for infrared detectors, and thermal-vidicons were calculated. The results indicated figures-of-merit of the composite film that were higher than pristine polyvinylidene fluoride film. The potential applications of composite films in medical devices are also discussed.

Simulation of energy harvesting from roads via pyroelectricity

Power harvesting is the process of extracting useful electrical energy from ambient low grade energy sources such as solar energy, mechanical energy, and thermal energy using smart materials as transducers. These materials have the ability to convert one form of energy into another. This paper aims at thermal-electrical energy converters based on a pyroelectric effect for energy harvesting, and examines its possible use in ultralow power devices and sensor modules. The present work investigates theoretically the energy harvesting capacity of pyroelectric samples fabricated in our laboratory and commercially available pyroelectric elements/transducers by capturing thermal energy of pavements. The single- and polycrystalline elements: triglycine selenate; lithium tantalate; modified lead zirconate titanate; modified lead titanate; modified lead metaniobate; and pyroelectric polymer nanocomposites such as Portland cement; nanocarbon fibers; polymer-lithium tantalate embedded with silver nanoparticles; and others were characterized for applicable performance parameters. The modeling and numerical simulation of energy harvesting capacity of these samples with the available pavements temperature-profile data over an extended period of time were investigated. The results indicate that the electrical energy harvesting via pyroelectricity is a feasible technique for powering autonomous low-duty electric devices.Based on our analysis of a single electric-energy harvesting unit, the triglycine selenate elements shall perform better than others with regard to the amount of voltage and energy densities extracted with respect to time. Possible future work and concepts of developing promising multidomain energy harvesters or hybrid harvesters are also briefly discussed.

Efficient planar perovskite solar cell by spray and brush solution-processing methods

Abstract. Perovskite compounds have the potential to transform photovoltaics technology, as they are easy to fabricate, have better stability, and possess superior power conversion efficiency. In this research, a versatile solution-processing method called “spray+brush” (SB) has been adopted to achieve a power-conversion efficiency of 3.52% for pure organometal halide perovskite devices. It has been observed that this method is more efficient and cost effective than the perovskite devices fabricated by spray (1.95%) and brush (1.17%) methods alone. The SB method of solution processing can be promising for various other organic coatings.

Holographic instrumentation for monitoring crystal growth in space

Refinements of holographic instruments for the First International Microgravity Laboratory Spaceflight, scheduled for February 1992, are described. The refinements include addition of holographic optical elements (HOEs) to incorporate tomographic analysis of the solution concentration and particle image displacement velocimetry to measure convection. A variety of advanced diagnostic instruments were designed for future spaceflights and possibly in the space station. These new instruments employ fiber optics, diode lasers, and HOEs to enhance miniaturization and ruggedness and to reduce power requirements. The instruments can measure concentration, temperature, convection, and crystal growth rate. Instruments currently in use as well as the conceptual designs and applications of future laser- and holography-based instrumentation are described.

Etch pit study of different crystallographic faces of L-arginine phosphate (LAP)

Abstract Etch pit studies have been made on different crystallographic faces of LAP single crystals. A new etchant has been developed which produces reproducible and good quality pits. The observed etch pits reveal the symmetry of different faces and the etching action somewhat depends upon the relative abundance of the various faces in the crystals grown from aqueous solution.