Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1-20 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 30-60 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature (T_C) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting P-E hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (ΔE) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.     

Iminodiacetic acid doped ferroelectric triglycine sulphate crystal: Crystal growth and characterization

Single crystals of iminodiacetic acid (HN(CH₂COOH)₂) doped triglycine sulphate (IDATGS) crystals have been grown from aqueous solution containing 1-10 mol% of iminodiacetic acid at constant temperature by slow evaporation technique. The effects of different amounts of doping entities on the growth habit have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the lattice parameters. The grown crystals were subjected to Fourier transform infrared (FTIR) spectroscopy studies to find the presence of various functional groups qualitatively. The dielectric permittivity has been studied as a function of temperature. An increase in the transition temperature (49.2-49.7 °C) of IDATGS crystals is observed. The dielectric constant (ε′_max) of IDATGS crystals vary in the range 922-2410 compared to pure TGS (T_c=49.12 °C and ε′_max=3050). Curie Weiss constants C_p and C_f in the paraelectric and ferroelectric phases were determined. The transition temperature (T_c) is found to decrease with increase in dopant concentration. P-E hysteresis studies show the presence of internal bias field in the crystal. Piezoelectric measurements were also carried out at room temperature. Domain patterns on b-cut plates were observed using scanning electron microscope. The micro hardness studies reveal that the doped crystals are harder than the pure TGS crystals. The low dielectric constant, higher transition temperature, internal bias field and hardness suggest that IDATGS crystals could be a potential material for IR detectors.     

Pyroelectric coefficient manipulation in doped TGS crystals

Pure and l-alanine doped Triglycine sulphate (TGS) crystals were grown in paraelectric phase (∼52 °C). Doped crystals show unequal growth rates along the ferroelectric axis. Pure TGS crystals show peculiar dielectric behavior in the ferroelectric phase, after crossing up and down the Curie point in two successive runs between room temperature and 80 °C. Much higher and unstable permittivity was found returning in the ferroelectric phase. At constant temperature (35 °C), permittivity follows a relaxation process, characterized by two relaxation times. l-Alanine doped TGS crystal shows more than one order of magnitude smaller permittivity and dielectric losses. Internal bias field of ∼1 kV/cm, induced by the dopant, made the crystal almost monodomain and pined polarization in one direction. Pyroelectric coefficient measurements were performed at constant heating rate of the samples, using a computer controlled He cryostat and Keithley 6517 electrometer. The temperature dependence of P⁺ polarization component, obtained by computer integration of the pyroelectric coefficient, was measured on a large temperature interval (−20/+80 °C). Pyroelectric coefficient of the doped samples was also measured by the same procedure, using a dc bias electric field, pointing in the opposite direction to the pined polarization. The polarization could be reversed, on the whole temperature range, by dc fields higher than bias or coercive field. Surprisingly, for the first time, the pyroelectric coefficient (p) was found constant on quite large temperature intervals. Doped TGS crystals show much smaller values of permittivity ?_r versus the pure one and consequently, get higher figure of merit M = p/?_r. The pyroelectric coefficient of this material can be tailored to become constant on a defined temperature range, under a dc field control. This characteristic makes this material valuable to be used as pyroelectric material for IR devices.     

Single crystals of triglycine sulphate containing palladium

Single crystals of TGS doped with Pd₂₊ have been grown from aqueous solutions using the method of temperature decrease. It was found that the relative growth rate along thec-axis is not constant through the growth process being larger by more than an order of magnitude (in medium size crystals, ca. 30 g) than in pure TGS crystals. Investigation of the domain structure revealed that in the growth pyramids ¦110¦, the crystals are poled in one direction. The internal bias field in these growth pyramids was experimentally found to be of the order of 1 kV/cm. The high internal field excludes the possibility of spontaneous depoling and makes the Pd²⁺-doped TGS crystals suitable for pyroelectric applications.     

Effect of uniaxial stress on the birefringence of triglycine sulphate crystals doped with L threonine

The temperature and spectral dependences of the birefringence ??n _i of triglycine sulphate (TGS) crystals with L-threonine impurity have been investigated. Doping with L-threonine is found to reduce the temperature dependence of ??n _i of TGS crystals. The baric coefficients of shift of the phase-transition (PT) point, ?T _c /???m, are found to be somewhat smaller than those for pure TGS crystals, which is confirmed by the increase in the hardness of TGS crystals after doping. The temperature and spectral dependences of the combined piezoelectric constants ?? _im ⁰ have been calculated. The stepwise changes in all piezoelectric constants at the PT of doped crystals are found to be much smaller than those for pure crystals.     

Refractometry of uniaxially compressed triglycine sulphate crystals doped with L-valine

The temperature and spectral dependences of the refractive indices n _i of triglycine sulphate (TGS) crystals doped with L-valine have been investigated. Doping is found to weaken the temperature dependence of n _i of TGS crystals. The electronic polarizabilities ?? _i , refractions R _i , and parameters of UV oscillators (??_0i , B _1i ) of mechanically distorted doped TGS crystals have been calculated. The temperature coefficients of the shift of the phase-transition point, ?T _c /??? _m , are found to be somewhat smaller than those for pure TGS crystals, which is confirmed by the increase in the hardness of TGS crystals after doping.     

Study of Properties of Urea and L-α-Alanine Didoped Triglycine Sulfate (UrLATGS) Crystals

In this report, the properties of triglycine sulfate (TGS) crystals doped with urea and L--alanine were studied. Urea and L--alanine have successfully entered into TGS crystal, demonstrated by infrared transmission spectrum and pyroelectric study. Figures of merit and Curie temperature are increased due to these two additions. UrLATGS is more suitable for infrared detectors than pure TGS crystals.     

A transverse electric current in triglycine sulphate ferroelectric crystal

The application of a prolonged transverse electric field at a temperature T_A < T_C leads to unexpected qualitative changes in dielectric and thermal properties of the uniaxial ferroelectric triglycine sulphate (TGS) crystal, where T_C is the critical temperature of the paraelectric-ferroelectric phase transition. The new properties can be still observed even after the transverse field has ceased to be applied as long as the temperature of the sample does not exceed T_A. However, annealing the sample above T_C leads to the restoration of the original state of the crystal. An electric current flowing along the direction perpendicular to the polar axis of the uniaxial TGS ferroelectric crystal was measured below the temperature T_A at which the prolonged transverse electric field had been formerly applied to the crystal for a few hours. The experimental data resemble the classic pyroelectric current flowing along the polar axis.     

Effects of nano-carbon doping and sintering temperature on microstructure and properties of MgB2

We fabricated nano-carbon (NC) doped MgB₂ bulks using an in situ process in order to improve the critical current density (J_c) under a high magnetic field and evaluated the correlated effects of the doped carbon content and sintering temperature on the phase formation, microstructure and critical properties. MgB_2−xC_x bulks with x = 0 and 0.05 were fabricated by pressing the powder into pellets and sintering at 800 °C, 900 °C, or 1000 °C for 30 min.We observed that NC was an effective dopant for MgB₂ and that part of it was incorporated into the MgB₂ while the other part remained (undoped), which reduced the grain size. The actual C content was estimated to be 68–90% of the nominal content. The NC doped samples exhibited lower T_c values and better J_c(B) behavior than the undoped samples. The doped sample sintered at 900 °C showed the highest J_c value due to its high doping level, small amount of second phase, and fine grains. On the other hand, the J_c was decreased at a sintering temperature of 1000 °C as a result of the formation of MgB₄ phase.     

L-α-alanine doped TGS under hydrostatic pressure

Abstract

A phenomenological model describing spontaneous polarization, pyroelectric, pressure-electric properties and dielectric permittivity of pure and 1-α-alanine doped TGS crystals is presented. Conclusions resulting from the model is illustrated by experimental data. Basic parameters of pressure-electric detectors and transducers made of doped or irradiated ferroelectric crystals can be estimated from the data determined for respective pure crystals.     

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

Good quality single crystals of pure and metal ion (Ni²⁺) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni²⁺doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni²⁺doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.     

Effect of an organic dye on the ferroelectric phase transition in KH2PO4 (KDP)

This paper reports on the first measurement of the dielectric permittivity and heat capacity of a KDP crystal doped by Chicago Sky Blue organic dye within a temperature interval including the ferroelectric phase transition at T _c =122 K. Similar measurements were made on a pure KDP crystal under the same conditions for the sake of comparison. The heat capacities of the pure and doped crystals were shown to differ substantially within an interval 1 K wide in the vicinity of T _c , where an anomaly in the heat capacity of the doped crystal was observed to wash out without producing any change in the temperature position of its maximum. The doping reduces the permittivity in the polar phase markedly. The observed effects are associated with the influence of nonisomorphic defects on the ferroelectric phase transition in a piezoelectric crystal.     

Pyroelectric nano-rods grown inside alumina nano-pores

This paper reports the formation and properties of nano-composite pyroelectric thin films. They consist of pyroelectric triglycine sulfate (TGS) single-crystal nano-rods grown inside a highly dense array of alumina pores (about 65 nm diameter and density of 1011 cm⁻²). The nucleation and growth of the TGS single crystals are obtained by precipitation from a supersaturated aqueous solution. Nucleation is preferred only at the bottom of the pores due to a tight control of temperature, composition and pore diameter. Growth of single crystals with preferred crystallographic orientation is obtained with the aid of an applied electric field. Various crystallographic orientations (1 0 0) (−1 1 0) (−1 2 0) are obtained separately as a single preferred orientation by changing the amplitude of the electric field during crystal growth. The films exhibit ferroelectric behavior.     

Growth,structural, mechanical,spectral and dielectric characterization of NaCl-added Triglycine sulfate single crystals

Pure and sodium chloride (NaCl)-added Triglycine sulfate (TGS) crystals were grown from aqueous solutions by slow evaporation technique. The values of concentration of dopants in the mother solution were 0.2, 0.6 and 1 mol%. The solubility of the grown samples have been found out at various temperatures. The determination of unit cell parameters was carried out by single crystal XRD method and found that the grown crystals crystallize in monoclinic structure. The dielectric characterization for the pure and NaCl-doped TGS crystals was performed by measuring the dielectric parameters like dielectric constant and dielectric loss with various frequencies in the range 10²–10⁶ Hz and with the temperatures ranging from 30 to 70 °C and this study reveals an increase of dielectric constant and loss with the increase of NaCl concentration. Studies on mechanical properties like microhardness and density of the grown pure and NaCl-doped TGS crystals were carried out. UV–Visible transmittance studies were carried out for the grown samples. A sharp fall in the transmittance is observed at 228 nm for pure and NaCl-doped TGS crystals. Atomic absorption spectroscopic (AAS) study was done on the NaCl-doped TGS crystals to ascertain the presence of Na⁺ ions in the lattice.     

Permanent polarization in pyroelectric TGS in detectors due to x-rays

The dielectric constant, pyroelectric coefficient, and loss tangent of triglycine sulphate (TGS) crystals that had been poled and subsequently irradiated with x-rays are presented as a function of x-ray exposure and temperature. The results are compared with similar measurements made on poled Co⁶⁰ gamma irradiated TGS. An estimated x-ray dosage of 1.5−2.0 × 10⁶ R min^-1 for 1–2 min gave equivalent results to 2.3 Mr of Co⁶⁰ gamma rays in achieving optimum non-ferroelectric pyroelectric in TGS ir detectors.     

Effect of annealing temperature on some physical properties of MgB2 by using the Hall probe ac-susceptibility method

A commercially available powder of MgB₂ is used as starting material for the examination of the influence of the annealing temperature on the properties of this intermediate-T_c superconductor. We performed scanning electron microscopy (SEM) and Hall ac-susceptibility measurements as a function of temperature and ac-field amplitude on samples annealed at 650, 750, 850 and 950 °C. The imaginary part of ac-susceptibility measurements is used to calculate both the inter-granular critical current density, J_c(T_p) and density of pinning force, α_j(0). It was observed that all T_c, J_c(T_p) and α_j(0) exhibit a non-monotonic behavior on the annealing temperature range studied in this work. T_c is measured to be 39.85±0.02 K and J_c(T_p) is estimated to be as high as 60 A/cm² at 39.2 K for the sample annealed at 850 °C. The peak temperature, T_p, in the imaginary part of the ac-susceptibility curves shifts to lower temperatures with both decreasing the annealing temperature and increasing the amplitude of the ac-magnetic fields. A comparison of the experimental ac-susceptibility data with theoretical critical-state models that are currently available is performed. SEM investigations showed that the grain size increases, and the grain connectivity improves when the annealing temperature increases up to 850 °C. The possible reasons for the observed changes in transport, microstructure and magnetic properties due to annealing temperature are discussed.     

Effect of xylenol orange on the crystalline perfection,optical, piezoelectric and NLO behavior of unidirectionally grown imidazolium L-Tartrate single crystal

Pure and 0.1 mol% Xylenol orange (XO) doped Imidazolium L-tartrate (IMLT) nonlinear optical (NLO) single crystals were grown using Sankaranarayanan–Ramasamy (SR) method of uniaxial solution crystallization technique. The pure IMLT crystal is 100 mm in length and 15 mm in diameter. The doped IMLT crystal is 25 mm in length and 10 mm in diameter. UV–Vis-NIR spectrum shows that the pure and XO doped IMLT crystals' cut off wavelength is 235 nm. High-resolution X-ray diffraction (HRXRD) measurement and birefringence interferometry confirm that the SR method grown crystal has good crystalline perfection and optical homogeneity. The wavelength dependent refractive index and piezoelectric d₃₃ coefficient were measured. The difference refractive index (Δn) of (100) plane in parallel and perpendicular directions shows a strong dependence on wavelength. The dielectric constant, hardness and SHG conversion efficiency were also increased as a result of XO dye doping in IMLT crystal.     

Growth and characterization of pure and doped organic nonlinear optical single crystal: l-Alanine alaninium nitrate (LAAN)

The pure l-alanine alaninium nitrate (LAAN) single crystals and LAAN crystals doped with lanthanum oxide (La₂O₃), sodium chloride (NaCl), urea (CH₄N₂O), glycine (C₂H₅NO₂) and thiourea (CH₄N₂S) were grown by slow evaporation method. The X-ray diffraction analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) analysis, UV–vis spectral analysis, dielectric studies and powder SHG measurement are studied systematically. The slight changes in the lattice parameters were observed for the doped crystals compared to pure LAAN crystal. The incorporation of doping into the crystal lattice was confirmed by energy dispersive X-ray analysis. There is no change in the transmission window due to doping and the percentage of transmission in doped samples was found to increase as compared to that of pure LAAN crystal. The dielectric constant of pure crystal was found to be less than that of doped crystals. The AC conductivity was found to increase after doping and with the increase in temperature. A green radiation of 532 nm was observed from the pure and doped LAAN crystals confirming the second harmonic generation (SHG) of the crystals.     

Effect of polymer relaxation on dielectric spectroscopic study of polymer–ferroelectric liquid crystal composites

Polymethylmethacrylate (PMMA) and ferroelectric liquid crystal (P–FLC) composite films (~ 4 μm) with varying proportions of ferroelectric liquid crystal have been prepared and the dielectric response of the composite films as a function of wide frequency (100 Hz–10 MHz) and temperature (127–40 °C) have been analyzed. The dielectric spectra of such composite systems are considerably modified compared to those of the corresponding pure LC or PMMA materials. The observed paraelectric to ferroelectric transition temperature of the composites is found to be lower (~ 85 °C) compared to that of the pure LC system (~ 98 °C), which makes these composites technologically more significant. The P–FLC composites also exhibit higher relaxation frequency and smaller dielectric strength for the Goldstone mode compared to those of the corresponding pure FLC. Depending on the percentage of the constitute materials, the molecular dynamics of the composite materials changes. Dielectric contributions of both liquid crystal and PMMA matrix forming the composites have been analyzed on the basis of Havriliak and Negami function.     

Optical spectra of triglycine sulfate crystals in the range of 7–33 eV and its changes at phase transition

Pseudo-dielectric functions ?ε₁(E)? and ?ε₂(E)? of triglycine sulfate (TGS) crystal have been obtained in the range of 7–33 eV for different temperatures close to ferroelectric phase transition by spectral ellipsometry using the synchrotron radiation source BESSY II. These dielectric functions ε₁(E) and ε₂(E) have also been calculated from first principles using CASTEP CAmbridge Serial Total Energy Package code together with the band structure and density of electronic states of the crystal. Experimental and theoretical dielectric functions agree satisfactorily. A characteristic decrease of temperature dependences of the dielectric losses tgδ(T) and related values just below the phase transition temperature T _c have been found and discussed.