TGS Crystals Research Articles

On Linear Birefringence Anomalies in Crystals of Triglycine Family

Temperature dependence of the linear birefringence in TGS crystal family has been studied with a high temperature resolution. Temperature derivatives of the linear birefringence are compared with the specific heat transients measured for triglycine sulphate, triglycine selenate, and triglycine fluoberyllate crystals. Detailed studies revealed an anomaly of the linear birefringence at about 310 K for two cuts (a*and c-cut) of the TGS crystal.

Two forms of polarization relaxation in polydomain ferroelectrics in an electric field

The characteristic features of the polarization and depolarization kinetics of polydomain ferroelectrics with square and narrow “extended” dielectric hysteresis loops are investigated for the model of TGS and Rb2ZnCl4 crystals. It is shown that for the second crystal, in contrast to the first crystal, the local free energy is asymmetric relative to the direction of polarization, the coercive field does not have a definite value, and only part of the crystal volume participates in the slow thermoactivational relaxation. The slow relaxation follows a universal empirical power law in all cases. The distribution functions of the relaxation times in crystals are constructed on the basis of experimental data, and comparative estimates are made of the relaxation parameters and the parameters of the energy barriers for domain walls.

Ferroelectric—superionically conducting phase transition via NMR

The comparative proton spectra of TGS crystals and a simple protein α-lactalbumin were obtained using High Resolution NMR. Both crystal and protein revealed 3 component spectra which were attributed to water and amino and carboxyl groups. The identity seen in both spectra let us conclude that proton mobility in TGS crystals under phase transition is as high as in liquids. The presence of fast moving protons in the vicinity of the phase transition temperature means that a polymorphous phase transition coexists with a high ionically conducting one.

The influence of constant electric field on relaxation processes due to the interaction of domain boundaries and mobile point defects in TGS

The dependencies of relaxation times τ1 and τ2 at constant electric field in TGS crystals were observed.

Low-Frequency Dielectric Dispersion of L-Threonine Admixtured Triglycine Sulphate Crystals (LTTGS)

For TGS crystals pure and admixtured with L-threonine, measurements of the permittivity ε and tg δ of the loss angle versus the measuring field frequency (varied from 1 to 104 kHz) were performed in the temperature range from 80 to 330 K. For the first time the low-frequency dielectric dispersion was observed in three temperature ranges: 180 to 210 K, 270 to 300 K and near the phase transition as the appearance of additional maxima of ε and tg δ. The interpretation of these maxima is given in combination with radiospectroscopic results. The dispersion in the three regions was interpreted as due to hindered rotation of NH3 groups of GI glycines (180 to 210 K), hindered rotation of NH3 groups of GII and GIII glycines and domain structure (270 to 300 K) and partial repolarisation of domains (near TC).

Low temperature thermal conductivity of Lu-admixtured TGS

The thermal conductivity of Lu-admixtured triglycine sulphate single crystals has been studied. Measurements over a wide temperature range (5–300 K) have been performed with the samples at intervals of about 0.5–10 K. No anomalies were observed in the range from 10 K to room temperature. It is therefore most probable that there is no low temperature phase transition in Lu-doped TGS crystals. Domain patterns on the b-plane and on the c-plane of Lu-doped TGS crystals have been studied through scanning electron microscopy. The domains in Lu-admixtured TGS are generally in the shape of rods oriented along the ferroelectric b-axis. That is the main reason for a strong anisotropy in the thermal conductivity.

Ferroelectric studies on amino acids mixed TGSP single crystals

Abstract Amino acids mixed TGS crystals are of interest due to their high pyroelectric coefficient and low dielectric constant. Partial substitution of phosphate has resulted in triglycine sulpho-phosphate (TGSP), a mixed crystal with improved pyroelectric figure of merit. In order to study the effect of amino acids on the ferroelectric properties of TGSP, we have substituted l-alanine (ATGSP), l-valine (VTGSP), l-asparagine (ASP-TGSP) and l-arginine (ARG-TGSP) in pure TGSP The pyroelectric studies and P-E hysteresis measurements carried out on these mixed crystals are reported. A scanning electron microscope in the secondary electron emission mode has been employed to visualize the domains on the mixed crystals.

Growth and stability of pure and amino doped TGS crystals

Pure and amino (L-alanine and L-valine) doped TGS crystals were grown by the slow cooling method. The rates of nucleation as indicated by the induction period were measured. Effects of dopants on the solubility, stability and induction periods were investigated in stirred solutions. The interfacial energy for pure and doped solutions at 30°C was calculated. High quality single crystals of dimension 9×5×4 cm 3 were grown.

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.

Dielectric and mechanical loss and mobility of domain walls

Three dielectric loss (D) and /or three mechanical loss (Q−1) peaks (P1, P2, P3) for KDP, TGS and LNPP (La1-xNdxPsO14) crystals have been investigated. P1 is attributed to the dynamic domains due to the fluctuation near Tc. P2 is related to domain walls (DWs). The Q−1 and D caused by the viscous motion of DWs are calculated, being fairly coincident with the experimental data of P2 peak in the kHz range. P3 peak drops down to zero rapidly in the low temperature side for TGS, and disappears in LATGS with mono-domain. So P3 is thought to originate from glass transition of pinned domain walls.

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.

Photovoltaic effects in TGS crystals

The investigation of photovoltaic effects in TGS crystals pure and doped with Fe in pulse and stationary regime of laser extitation have been carried out. The mechanisms of photoresponse were identificated: piezoelectric, pyroelectric and photo-induced dipole moment effect.

Electron emission of ferroelectrics induced by ac electric field in the vicinity of the phase transition

The results of electron emission investigations for different ferroelectric materials are presented. This unipolar electron emission, induced by a low frequency ac electric field, was measured in the vicinity of the phase transition temperature of TGS, TAAP and BaTiO3 single crystals as well as (Ba, Pb)TiO3 and PLZT-5.1/65/35 ceramic samples. The mechanisms of this electron emission for both the ferroelectric as well as paraelectric phase are discussed.

Surface potential of Fe3+ admixtured tgs crystals

The surface potential of TGS crystals doped with the trivalent iron ions was investigated by the induction probe technique. The measurements were carried out for the crystals containing various concentrations of Fe3+. The influence of admixture concentration on the magnitude and decay of the surface potential was found. The applied method is effective to study the distribution and dynamics of electric charge on isolated surface of the crystal.

Influence of the internal bias field on the movement of the domain walls in (CH 3 NH 3)5 Bi 2 Br 11 crystals

The effect of internal bias field on the field - induced movement of the domain walls in (CH 3 NH 3)5 Bi 2 Br 11 crystals has been investigated using liquid crystal decoration technique (NLC). The measurements were carried out in dc - electric field and alternate square pulses of electric fields. Comparison was made of the nucleation process in (CH 3 NH 3)5 Bi 2 Br 11 and TGS crystals. The difference was explained in terms of difference of activation energy for domain wall motion.

Change of the Normal Rate of Hills Growth on the (001) Face of TGS Single Crystal Under Constant Crystallization Conditions

AbstractConsiderable change (up to 100% in one of the cases) of the normal growth rate of hills on the (001) face of the TGS crystal at strictly constant supersaturation and temperature is registered experimentally.On the basis of the spatial disposition of the dislocations, which form the source of the steps, a model of a growth centre (called herein non‐parallel centre of growth) is proposed. The model is qualitatively concordant with the experimental data.It is shown that the inconstancy of the normal rate of growth at constant supersaturation and temperature is an immanent characteristic of the non‐parallel centre of growth.

The effect of D-phenylalanine admixture on dielectric properties and domain structure of TGS crystals

The effect of D-phenylalanine admixture on dielectric properties and domain structure of TGS crystal was studied. Temperature measurements of permittivity of the samples were performed for selected frequencies of the measuring field, with and without an external constant electric field. Moreover, temperature measurements of spontaneous polarization and coercive field were carried out for samples of different concentration of D-Phe admixture. With increasing concentration of the admixture in the solution from which the studied crystals were grown the values of maximum permittivity and spontaneous polarization decrease while the coercive field increases. Domain structure of the DPTGS crystals was observed in the process of spontaneous ageing by the liquid crystal method.

Activity of nonparallel center of growth of (001) face of TGS single crystal under inconstant conditions of crystallization

AbstractMorphologic and kinetic behaviour of the hill of the (001) face of TGS crystal, generated by unparallel dislocation center of growth under inconstant supersaturation and temperature has been experimentally examined. Some irreversible changes in the shape of the hill top, as a hysteresis in its normal rate of growth is registered. A model, on the base of which a qualitative anylsis of the phenomenon is proposed.

Chaos in hydrogenous ferroelectric crystals

Abstract Investigation of forced chaotic oscillations in an RLC-circuit with TGS and DTGS crystals as a non-linear capacitance have been carried out

Temperature dielectric anomalies of triglycine sulphate crystals admixtured with L-α-alanine at different frequencies of the measuring field

Abstract The permittivity ϵ′ and loss tangent tg δ were measured for TGS crystals admixtured with different amounts of L-α-alanine, in a measuring field with frequencies varying from 1 kHz to 10000 kHz and for temperatures from 100 to 330 K. With increasing amount of L-α-alanine admixture, the low temperature maximum decreases, and for the crystal with the maximum concentration of L-α-alanine it disappears.