Pure TGS Crystals Research Articles

Influence of a static magnetic field on the dielectric properties of triglycine sulfate

The influence of a static magnetic field on the permittivity ε of pure TGS crystals has been studied. There is no of the magnetic effect when the vectors B and PS are collinear, it exists when B and PS are mutually orthogonal and it is greater when B is oriented along a-axis. After the magnetic field is turned off, the values of ε first increase up to the maximum observed of about 30–40 h, and then a long recovery to the initial values of ε occurs. Possible mechanisms of influence of the magnetic field on the studied crystals are discussed.

Peculiarities of the Dielectric Spectra of Triglycine Sulfate Crystals with a Profile Distribution of Chromium

The temperature evolution of the dielectric spectra of TGS–TGS + Cr crystals (TGS stands for triglycine sulfate) with a periodic distribution of chromium impurity (Cr3+) has been studied in comparison with nominally pure TGS crystals in the frequency range from 10 to 107 Hz upon heating and cooling. It is shown that impurity crystals are characterized by the absence of dielectric dispersion in both measurement modes. An approach is proposed to explain the peculiarities of the dielectric dispersion of crystals with a periodic distribution of chromium impurity from the standpoint of mobile activity of certain elements of the TGS crystal structure.

Enhanced ferroelectric properties and crystal structure of TGS0.74P0.26 single crystals

The single crystals of triglycine sulpho phosphate (TGS0.74P0.26) were grown by slow evaporation method with 0.6 M of phosphoric acid in the growth solution. The crystal structure of the grown crystal is refined with 0.74 sulphur and 0.26 phosphorous occupancy with the formula of TGS0.74P0.26 using single crystal x-ray diffraction analysis. The dielectric, ferroelectric and pyroelectric properties of the TGS0.74P0.26 single crystals were investigated. The coercive field (Ec) and internal bias field (Ib) values are 8 kV/cm and 1.4 kV/cm, respectively and these values are found increased compared to the pure TGS and also low dielectric loss was observed. The pyroelectric coefficient of TGS0.74P0.26 crystal is 0.023 µC/cm2/°C and the pyroelectric figure of merit for current, voltage and detectivity are Fi = 105 pm/V, Fv = 0.055 m2/C and Fd = 22 µPa−1/2 respectively. Enhanced ferroelectric properties were observed when compared to the pure TGS crystals. The figure of merit for the detectivity (Fd) shows higher values when compared with that of the well-known materials such as PZT (11.5 µPa−1/2) and other lead free materials such as SBN (7.21 µPa−1/2) and CSBN (12 µPa−1/2). With these excellent properties, the TGS0.74P0.26 single crystal can be a promising material for the pyroelectric detector applications.

Thermal and surface studies of unidirectional grown nickel sulfate added triglycine sulphate single crystal

Triglycine sulfate crystal added with 0.5 mole% nickel sulfate of 15 mm diameter and 150 mm height has been grown from an aqueous solution using Sankaranarayanan–Ramamasamy (S‐R) method in [001] direction. The grown crystal was studied by various characterization techniques. Thermogravimetry analysis reveals that the NiSO4 added TGS crystal is more thermally stable than pure TGS crystal. The presence of nickel in the TGS‐NiSO4 crystal was confirmed by atomic absorption spectroscopic (AAS) technique and its concentration was found to be 284 ppm. The surface of the grown crystal was investigated using atomic force microscope (AFM). It revealed the surface defects of the doped TGS crystal.

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

Single crystals of iminodiacetic acid (HN(CH 2COOH) 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.

Improved ferroelectric and pyroelectric parameters in iminodiacetic acid doped TGS crystal

Single crystals of Iminodiacetic acid (HN(CH 2COOH) 2) doped Triglycine sulphate (IDATGS) has been grown from aqueous solution at constant temperature by slow evaporation technique. The concentration of the dopant in the TGS solution was 2 mol%. The X-ray diffraction analysis indicates that there is significant change in the lattice parameters compared to pure TGS crystal. The IDATGS crystal has larger transition temperature and observed higher and uniform figure of merit over most part of the ferroelectric phase. These crystals also exhibit higher internal bias field and micro-hardness number compared to pure TGS. Therefore IDATGS may be a potential material for IR detectors.

Raman Scattering and Electrical Properties of TGS:PCo (9%) Crystal as Ambient Temperature IR Detector

We developed and adequately characterized the triglycine sulfate family crystals doped with specific molar percent of cobalt phosphate, TGS:PCo (9%). The crystals were grown by slow evaporation technique and the growth rates of different crystallographic planes are rather faster in comparison with the plane growth rates of pure TGS crystals. The introduction of Co ion as an active optical element to the structure of TGS crystal leads to optimization of some parameters such as optical quality, stability at ambient condition, Curie temperature, stronger Raman peaks, etc. Three new peaks at 460, 620 and 1368 cm−1 were observed in the dispersive back scattering Raman spectra of the grown TGS:PCo (9%) crystal in comparison with the pure triglycine sulfate crystal.

Electron Emission from the Surface of TGS Crystals with Different Domain Structure

A relation was established between the emission signal magnitude and the domain structure type in nominally pure TGS crystals and TGS crystals with various impurities: europium and chrome ions. It was demonstrated that in non-unipolar samples with numerous domain walls an electron emission is either very weak or is absent at all. The obtained results can be explained in the framework of cold emission from ferroelectrics.

Swift heavy ion induced modification on the dielectric behaviours of pure and doped TGS crystals

Swift heavy ion beam irradiation has been used for creating the non-equilibrium condition in the ferroelectric crystals of TGS doped with alanine impurities. Dielectric measurements reveal that irradiated crystals retain their ferroelectric phase and Tc remains invariant. Dielectric peak, however, gets broaden and decreases with increasing fluence. Tangent loss also decreases. Dielectric dispersion in different crystals show interesting changes with fluence and is analyzed in terms of thermally generated electric field in the crystals that stabilizes the bi-domain structure.

The Refractive Properties of Uniaxially Stressed Doped TGS Crystals

The effect of uniaxial mechanical stresses applied along the principal crystal-physical axes on the principal values of birefringence Δ n i is studied on TGS crystals with L-threonine, L-valine and D-serine admixtures. It is revealed that Δ n i are quite sensitive to the stresses and have different values and opposite signs. The baric coefficients ∂Tc/∂ σm for the phase transition (PT) temperature appear to be smaller than those for the pure TGS crystals. Temperature and spectral dependences of the combined piezooptic constants are calculated.

Thermostimulated Electron Emission in Paraelectric Phase of TGS Crystals with Nickel Admixture

Thermostimulated electron emission from ferroelectric TGS crystal with an admixture of nickel was experimentally detected in the temperature range exceeding Curie point by ∼10 K for the samples heated with rather high rate. An increase of the heating rate q was shown to result in an increase of the emission current in the entire investigated temperature interval. In TGS crystal with nickel admixture the temperature of emission appearance insignificantly depends on the rate q and is close to the case of pure TGS. The temperature of disappearance of emission monotonously increases with q. The interval of pulling of emission to paraphase here is less than for a case of pure TGS heated with the same rate. Peculiar features of emission in the investigated crystal can be explained by the relaxation of screening charges of spontaneous polarization. Less temperature of termination of the emission in TGS crystal with nickel admixture as compared with pure TGS crystal is explained by less Maxwell relaxation time in the doped crystal. The work was made under support of VZ-010 grant intended for creation of Research Educational Center “Wave processes in non-homogeneous and non-linear media” and INTAS grant “Ferroelectrics templated in nanoporous membranes.”

Kinetics of Electron Emission from Ferroelectrics

Kinetics of thermostimulated emission in ferroelectric crystals is examined. It is shown that in pure TGS crystals characteristic emission relaxation time depends on temperature, and decreases as one approaches the phase-transition point. The relaxation time of emission signals in crystals enriched with impurities is several times less than in pure materials and does not depend on temperature. Thermally stimulated electron emission is experimentally observed in TGS crystals, in a temperature range with upper limits of 10–15 𝒦 above the Curie point. The reason for the occurrence of emission above the Curie point is related to slow relaxation of the screening charges, which persist in the paraelectric phase.

Growth of thiourea-doped TGS crystals and their characterisation

Thiourea-doped Triglycine sulphate (ThTGS) crystal with three different concentrations of thiourea was grown from aqueous solution by slow cooling technique. The cell parameters were determined from powder X-ray diffraction analysis. A qualitative analysis of the presence of thiourea in doped crystals was estimated by FTIR analysis. Microhardness studies were carried out using Leitz Weitzler hardness tester at room temperature. Dielectric properties of the crystals were studied which showed a shift in the T c when compared to pure TGS crystal. Pyroelectric studies were carried out and the pyroelectric coefficient was found. Piezoelectric studies ( d 33 coefficient) has also been carried out.

Fundamentals in ferroelectric transition of TGS

An extended Landau type-model has been used to find the three-terms polynomial expansion of the Gibbs free energy, that describe the second-order phase transition in pure TGS crystal. Temperature dependence of the coefficients was calculated using experimental susceptibilities and polarization, measured on a large temperature range. In a second version of the model, the influence of the external electric field was considered. The third coefficient δ E gets negative values near the Curie point. Gibbs free energy curves G E ( P, T), versus polarization, show peculiar behaviour depending on an external electric field, in the temperature range 3–5°C near the Curie point. The share contribution of the electric field 1.5 kV/cm, exceed 100% at Δ T= T C− T <1.5°C. All curves become asymmetrical and the external barriers of the double minimum potential, for Δ T⩽4°C, show turning points for values smaller than k B T. The central barrier, at Δ T<25°C, is about two orders of magnitude smaller than k B T. The energy corresponding to the internal field E int≈ P S/3 ε 0, is higher or comparable to k B T, only at Δ T⩾10°C. The equation of state E( P, T), which is supposed to represent the hysteresis loop P( E), does not give the right order of magnitude of the measured coercive field. On this ground and according to some other literature data, we conclude that the free energy G( P, T) of TGS is a non-analytical function. Some other models, taking into account short and long-range interaction, have to be considered.

The Effect of D- and DL- Tyrosine Admixture on Dielectric Properties of TGS Crystals

Single crystals of TGS admixtured with L and DL- tyrosine (abbreviated as LTyrTGS and DLTyrTGS) were grown from a solution containing 0.7, 1 and 1.4 wt% of tyrosine relative to pure TGS. Temperature measurements (5 - 340 K) of permittivity l and loss tangent tg i of the samples were performed at selected frequencies of the measuring field varied from 1 kHz to 13 MHz. The values of spontaneous polarization P s , coercive field E c and bias field E b were obtained from the hysteresis loop. With increasing concentration of the dopands in the admixtured crystals, the values of l max and tg i max decreased, while that of the bias field and coercive field increased, and the Curie temperature revealed insignificant changes. The domain structure observations proved a refinement of the domain structure relative to that in pure TGS crystals and a decrease in the time of spontaneous ageing. The actual amount of the admixtures in the crystals was determined by UV spectroscopy.

Growth and characterisation of l-cystine doped TGS crystals

Single crystals of l-cystine doped triglycine sulfate (LCTGS) were grown from aqueous solution by low temperature solution growth technique. Morphological changes were observed on the grown crystals. Crystalline quality and cell parameter values were found using rocking curve and powder X-ray diffraction analysis, respectively. The presence of l-cystine in LCTGS was estimated qualitatively by FTIR analysis. Microhardness studies were carried out using Leitz Weitzler hardness tester at room temperature. The dielectric studies were carried out to identify the phase transition temperature and to find the dielectric constant. P-E hysteresis studies were done to find the values of spontaneous polarisation and coercive field for both pure and doped TGS crystals. Scanning electron microscopic investigations on uncoated b-cut plates were carried out to visualise the lenticular domains. AFM studies on the cleaved b-cut plate were carried out to understand the ferroelectric surface and the domain structure.

Study on the Growth and Properties of Guanidine Doped Triglycine Sulfate Crystal

Guanidine doped TGS crystal is grown from the aqueous solution. The pyroelectric properties of GTGS crystal are studied, the result shows that GTGS crystal has better pyroelectric properties than those of pure TGS crystal. The effects of organic dopant on pyroelectric properties of TGS crystal are discussed.

Thermal diffusivity of Lu- doped TGS in the ferroelectric phase

The temperature dependence of the thermal diffusivity (ThD) of TGS doped with Lu3+ was investigated in two crystallographic directions in the ferroelectric phase. The thermal diffusivity was calculated at different temperatures from the relation k = Λ/cP p. The measurements of the thermal conductivity (Λ) were performed using a steady-state measuring method. The results show that ThD is closely related to the impurities and imperfections. The marked changes in ThD at low temperatures of Lu-doped TGS crystals compared with the ThD of pure ones suggest the perturbation of the crystal lattice by point defects - Lu3+ ions.In the range of low temperatures - below 50K. the ThD is lower in the ferroelectric [010] direction for pure and Lu-doped TGS crystals both. Domain patterns on the [010]-plane and on the [100]-plane of pure and Lu-doped TGS crystals have been studied through scanning electron microscopy. The domains in pure and Lu-admixtured TGS are generally in the shape of rods oriented along the ferroelectric axis.

Ferroelectric properties of pure and doped triglycine sulphate crystal

Permitivity and losses of pure TGS crystal show a peculiar behaviour crossing up and down the Curie point between room temperature and 60 °C in two successive runs. The TGS:LD alanine doped crystal show peculiar hysteresis loops, composed of three elementary cycles due to a “free switching” component P′ and two other non-equivalent components PA and PB of opposite directions pinned by dopants. They change their shares in the hysteresis loop versus AC electric field and the pinned components retain up to 20% of the polarisation for pure TGS at saturation. The coercive and the bias fields of the two pinned components show different behaviour both for increasing AC field and temperature, suggesting a non-equivalent alanine substitution in the crystal lattice.

An approach for studying natural unipolarity in doped and pure single TGS-crystals

An investigation was made to study the dependence of the magnitude and direction of the pyroelectric current on the internal biasing field and natural unipolarity for both pure and doped TGS single crystals. The effect of applying poling electric fields, both parallel and antiparallel to the direction of the natural unipolarity, on the behavior of pyroelectric current was also inspected. A negative pyroelectric current was observed during the second subsequent heating runs for pure TGS crystal and for one, with Co+2 doping. For one pure sample, pyroelectric current followed the direction of the direction of the applied poling field, while for another pure one taken from a neighboring site, this was not the case. Stronger electric fields were needed to overcome the internal biasing field, in order that the pyrocurrent may be able to follow up the direction of the poling field. On the other hand, for a crystal doped with Co+2 ions, even a poling field of up to 4KV/cm was not enough to overcome the internal field; the sample retained its behavior. All the observed irregularities were attributed to the influence of the internal field together with the crystal inhomogeneity.