Ravindra B. Lal

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.

Holographic flow field analysis in Spacelab-3 crystal growth experiments

Holographic flow field analysis has been applied in a crystal growth experiment conducted on NASAs space shuttle program on Spacelab-3 during April 29 - May 6, 1985. The experimental holograms taken during the crystal growth process are reconstructed into interferograms and later digitized to give refractive-index fields: A comparison has been made with theoretically computed interferograms.

Growth and characteristics of tgs crystals grown aboard first international microgravity laboratory (IML-1)

Abstract The growth and detector characteristics of TGS crystals grown in a low gravity environment of space are presented. High resolution monochromatic synchrotron X-ray diffraction imaging of the space grown crystal indicates an extraordinary crystal quality.

Crystal growth and investigation of efficient non-linear optical materials in the mixed (2,-4-dinitrophenyl)-L-alanine (DPA) and 2-methyl-4-nitroaniline (MNA) system

When a 1∶1 weight mixture of (2,-4-dinitrophenyl)-L-alanine (DPA) and 2-methyl-4-nitroaniline (MNA) is dissolved in a 50∶50 volume mixture of ethyl acetate and hexane, two types of crystals were observed on slow evaporation. In the first stage of crystallization, light-yellow plates of MNA measuring up to 25 mm×5 mm×1 mm were formed, which belong to the triclinic space group P1 with lattice parameters a=0.7621 (3) nm, b=0.795 2(5) nm, c=0.8200 (2) nm, α=111.84(2)°, β= 93.76(2)°, γ=116.84(3)°, Z=2. The volume of the unit cell containing two molecules is 361.9(1)×10−3 nm3. The powder SHG efficiency of the triclinic polymorph (MNA(T)) is about the same as that of the monoclinic MNA(M). The Raman spectrum of the new crystal is similar to that of MNA(M) crystallized from the vapour phase or solution, except for the change in the intensity of a few bands. The DSC data show minor differences in the melting points and specific heats for the two phases. The second stage of crystallization resulted in the formation of orange-yellow coloured crystals of the DPA:MNA complex, in the monoclinic space group P21 with lattice parameters a =0.6876(1) nm, b=0.7621(3) nm, c=1.7626(4) nm, β=96.62(2)°, V=917.5 ×10−3 nm3, Z=2 for C16H17N5O8. The Raman spectrum of DPA:MNA consists of bands from both DPA and MNA. The complex melts at 138(1)°C with a specific heat of 25.3(4) cal g−1 according to the DSC measurements. The powder SHG efficiency is nearly the same as that of methyl-(2,4-dinitriphenyl)-aminoproanoate (MAP).

Multifunctional organic flexible nanocomposite sensors for biomedical applications

The multifunctional flexible nanocomposite films were developed and characterized. To improve the sensitivity, the novel P(VDF-TrFE) film-sensors embedded with carbon nano-particles were synthesized and fabricated via the solution casting technique. The fabricated films were characterized for dielectric, piezoresistive, and pyroelectric properties so as to predict performance of the sensors for pressure, thermal detection, and energy harvesting. The results obtained are presented and discussed.

Electrical properties of TGS crystals grown by a new technique

The cooled sting technique used to grow triglycine sulphate (TGS) crystals is investigated. The sting procedure, which achieves supersaturation by cooling the seed crystal mounted on the sting is described and a diagram is provided. Temperature differentials of 1.5 and 1.0 C are optimum for growing (001) and (010) orientation TGS seeds. The data obtained are compared with previous data and good correlation is shown; it is inferred that TGS crystals of any orientation can be grown at a uniform rate of 1 mm/day using this technique.

Growth of triglycine sulfate (TGS) crystals by solution technique

The growth of crystals from solution is greatly influenced by buoyancy driven convection. In a low-g environment, convection is greatly suppressed and diffusion becomes the predominant mechanism for thermal and mass transport. An experiment to grow TGS crystals by solution technique during the orbital Spacelab III mission has been designed. Crystals are grown by a new and unique technique of extracting heat from the crystal through a sting. The cooling at the sting tip is responsible for the desired supersaturation near the growing crystal. Calculations indicate that the cooled sting technique for solution crystal growth is necessary in low-g to maintain a maximum growth rate of 1 mm/day. Results of groundbased work in support of the flight experiment are discussed.