G. Arunmozhi

Crystal growth and characterization of a new nonlinear optical material: Urea L-Malic acid

A new nonlinear optical organic crystal, viz. Urea L-Malic acid, has been grown from aqueous solution employing the techniques of solvent evaporation and slow cooling. The grown crystals were found to be transparent in the visible region. The complete morphology of the crystal has been worked out and its hardness was evaluated using Vickers indentation method. The grown crystals were characterized employing several techniques such as micro-carbon-hydrogen-nitrogen analysis, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, UV-VIS-IR spectroscopy and refractive index measurement. Preliminary measurements indicate that the second harmonic generation efficiency at a fundamental wavelength of 1064 nm is roughly three times that of KDP.

Ferroelectric properties of TGS crystals grown under an intense DC electric field

The application of electric field during crystal growth modifies the ferroelectric properties of triglycine sulphate (TGS) crystals. Scanning electron microscopic examination of freshly cleaved (0 1 0) surface shows the presence of some domains tilted with respect to the c-axis. It is suggested that the cause of the onset of domains misaligned with the c-axis is the partial pinning by the field of the rotation of the NH3 group of the glycine I molecule. The modified domains originate a decrease of the dielectric values, a reduced spontaneous polarization and an increase of the relaxation times. Crystals of TGS grown under field remain in a stable state with modified properties as long as they are not subjected to intense AC fields or annealed above the Curie temperature for more than two cycles. r 2002 Elsevier Science B.V. All rights reserved. PACS: 77.80.Dj; 77.84.� s; 77.84.Fa; 77.80.� e; 81.40.Rs

Antiferroelectric ADP doping in ferroelectric TGS crystals

Crystal growth, morphology, hysteresis and dielectric measurements on 20 mol% ammonium dihydrogen phosphate (ADP)-doped triglycine sulphate (TGS) crystals are reported. Crystals grew with morphology similar to phosphoric acid-doped TGS (TGSP). Inhomogeneous incorporation of dopants gives rise to a distribution in coercive fields in the different growth sectors. The incorporated dopant hinders polarization switching, which results in the increase in coercive field. No internal bias field is created by the dopant and the phase transition observed is similar to pure TGSP. The Curie point shifts to a lower temperature with increasing dopant concentration in the growth sectors. Significant changes in the activation energies of annealed specimen were identified.

Electrical characterization on l-tyrosine doped triglycine sulfate single crystals

Abstract Dielectric, hysteresis, and scanning electron microscope studies on l -tyrosine doped triglycine sulfate (TyTGS) are reported. Increase in the relative permittivity compared to triglycine sulfate is observed on the doped crystal. Low frequency dielectric relaxation process is found to be modified in TyTGS crystals. No significant change in the spontaneous polarization compared to pure triglycine sulfate is observed. Increase in the coercive field in TyTGS compared to pure triglycine sulfate suggests that the dopant hinders the domain wall motion. Lens shaped domains, typical of triglycine sulfate are also observed on TyTGS crystal.

Synthesis and characterization of a salt of sodium with L-malic acid: A new ferroelectric?

A new inorganic malate salt NaL-Malic acid has been synthesized. Elemental analysis suggests that the compound has the empirical formula NaC4H5O5. This compound is presumed to be analogous to tartrate salts, which have interesting nonlinear optical and ferroelectric properties. The extensively investigated Rochelle salt is a salt of sodium and potassium with tartaric acid and has interesting ferroelectric properties. Preliminary thermal and dielectric measurements of the NaL-Malic acid salt show the existence of three reversible phase transitions located approximately at the following temperatures 310 K, 325 K and 360 K. The lattice parameters for the crystal structure at room temperature, obtained from X-ray powder diffraction, are also reported.

Dielectric properties of L-asparagine doped TGS (Asp-TGS) crystals

Low frequency dielectric properties of TGS doped with a new dopant L-asparagine and its influence on the dynamics of the TGS system is reported. L-asparagine doped TGS (Asp-TGS) crystals exhibit lower dielectric permittivity compared to pure TGS. The ratio of the Curie constant indicates partial pinning of the domains by the dopants. The tg δ maxima observed in the studied temperature range are explained in terms of the hindered rotations of the glycine groups in the crystal structure.

Dielectric relaxation in pure and irradiated TGSP crystals

Abstract Low frequency dielectric measurements in triglycine sulpho-phosphate (TGSP) and gamma-irradiated TGSP crystals were carried out around the ferroelectric to paraelectric phase transition. The dispersion found in the ferroelectric phase cannot be explained only by a Debye equation with a single relaxation time. The ratio of the Curie constants in the para- and ferroelectric phase ( C p / C f ) for the irradiated TGSP samples show that the crystal is partially clamped. The deviations from the typical single relaxation behaviour are more pronounced in irradiated samples clearly indicating the contribution of defects in addition to the impurities to the dynamics of the system.

Pyroelectric Properties of AspTGS Crystals

Pyroelectric properties of 10 mole% L-asparagine doped TGS crystals are reported. Doping in the TGS crystal with polar molecules results in modifications in the spontaneous polarization, creation of an internal bias field Eb, which like an external field tends to keep the crystal in single domain state. The dopant concentration in the crystal has a significant influence on spontaneous polarization and the strength of the internal bias field.

Modification of the Dielectric Properties of TGS Crystal Grown Under the Influence of DC Electric Field with Different Strengths

TGS crystals grown under two different dc electric field strengths exhibit modified ferroelectric properties. The modifications show a dependence on the field strength applied during crystal growth. Prominent modifications were observed on crystals grown at high fields (80 kV/cm) than in crystals grown under lower dc electric fields (10 kV/cm). The modified ferroelectric properties stem from the domain structures influenced by the applied field. The domains on the low field grown crystals are more elongated and appear as thin strips. In the case of high dc field grown crystals, some of the domains are tilted under the influence of the field, resulting in the misalignment of the major axis of the domains with respect to the c-axis. The domain structure modifications under the influence of fields lead to an increase in the relaxation times. Reduced dielectric permittivity and spontaneous polarization also illustrate the effect created by the field.

Modification of Ferroelectric Properties of TGS Crystals Grown under a dc Electric field

Ferroelectric triglycine sulphate crystals have been grown under the influence of an intense electric field of 6×104 V/m. Relative to crystals grown under ambient conditions (TGS) the crystals grown under the electric field (TGS-E) display a dielectric permittivity a factor of two lower. Significant differences are observed in the Curie-Weiss behavior of the ferroelectric phase, in the x-ray diffraction patterns and in the differential calorimetry measurements.