Ferroelectric Triglycine Sulfate Research Articles

Thermally stimulated electron emission from chromium-doped triglycine sulfate in the paraelectric phase

Thermally stimulated electron emission from a ferroelectric chromium-doped triglycine sulfate (TGS) crystal was experimentally observed to occur in a temperature range 6 K above the Curie point from samples heated at a relatively high rate. Increasing the heating rate q was shown to cause the emission current density to increase throughout the temperature range studied. The emission onset temperature in chromium-doped TGS depends only weakly on the rate q and is close to that for pure TGS, and the emission cutoff temperature grows monotonically with q at comparatively low heating rates and stabilizes at high q. At the same time, the interval of emission extension into the paraelectric phase here is about one half that for pure TGS heated at the same rate. The specific features of emission observed for this crystal can be assigned to relaxation of the charges screening the spontaneous polarization. The lower emission cutoff temperature for the chromium-doped TGS compared to that for pure TGS is accounted for by the shorter Maxwellian relaxation time in the doped crystal.

Stochastic Resonance and Domain Switching

Triglycine sulfate (TGS) is the first ferroelectric material that has been reported to exhibit the effect of stochastic resonance. We observed the effect experimentally, varying the noise strength added to a periodic signal, that was too weak to cause switching between the two possible states of polarization in ferroelectric TGS. Despite the fact that most of the theoretical predictions could be confirmed in our experiments, there occured some peculiarities that have not been observed in other systems with stochastic resonance. The most obvious effect is the dependence of the spectral amplification and the signal-to-noise-ratio on the direction of noise variation. It can be explained taking into account the mechanism of domain switching in ferroelectric materials.

Selective Effect of Weak Magnetic Field on Triglycine Sulfate Crystal

Selective effect of weak permanent magnetic field on nominally pure ferroelectric triglycine sulfate crystal has been observed for the first time. The prolonged changes of permittivity and Curie point were observed after short-term treatment of the crystal in a narrow interval of magnetic field ∼0.1 T . The effect is explained by magnetic field assisted depinning of domain walls from point defect clusters by spin-depended mechanism similar to depinning of dislocations from paramagnetic obstacles in magnetoplasticity. The point defect clusters are assumed to be H-bonded ones.

Formation of an internal bias field in chromium-and L, α-alanine-doped triglycine sulfate crystals

The unipolar state of a chromium-and L, α-alanine-doped ferroelectric triglycine sulfate (TGS) crystal has been studied. The experimental data on the distribution of internal bias fields with respect to a seed are considered. The possible mechanisms of the formation of an internal bias field during the growth of TGS crystals with a low impurity concentration are considered.

Temperature-induced orientational transition of nematics on the surface of a ferroelectric crystal

A temperature-induced orientational transition is investigated in a mixture of nematic liquid crystals on the surface of a cleavage of a ferroelectric triglycine sulfate crystal. The transition has been observed by the variation of the polarized absorbance components of a dye introduced into the nematic matrix with increasing temperature. The reorientation of molecules in the liquid crystal volume confined by solid walls is due to competition between dispersion and polar forces at the surface and the decrease in the electric field of the substrate up to its complete disappearance at the ferroelectric Curie point.

Thermally stimulated electron emission in the paraelectric phase of triglycine sulfate crystals heated at a high rate

Thermally stimulated electron emission is experimentally observed in ferroelectric triglycine sulfate (TGS) crystals in a temperature range whose upper limit is 10–15 K above the Curie point. Samples of a nominally pure and a chromium-doped TGS crystal, heated at different constant rates q=dT/dt, are investigated. It is shown that an increase in the heating rate results in increased emission current density over the entire temperature range investigated. The temperature at which emission arises depends only slightly on the rate q. At the same time, the temperature at which emission ceases increases monotonically with increasing q; if q is less than 1 K/min, this temperature is below the Curie point, while at q=4–5 K/min, this temperature becomes as large as 60–65°C, which is more than 15°C above the Curie point. In chromium-doped TGS crystal, the electron emission onset temperature is close to that of pure TGS, but the width of the temperature range over which emission is observed in the paraelectric phase is approximately two times less than in the case of pure TGS heated at the same rate. The emission disappearance below the Curie point (in the ferroelectric phase) at low q is explained as a result of full emptying of the electron traps under slow heating. The reason for the occurrence of emission above the Curie point is related to the charges that shield the spontaneous polarization and, because of their slow relaxation, persists in the paraelectric phase.

Structure of the polar (010) cleavage of a ferroelectric TGS crystal from the atomic-force microscopy data

The atomically smooth polar (010) cleavage of a ferroelectric triglycine sulfate (TGS) crystal has been studied by the method of atomic-force microscopy. It is shown that the rounded 0.6-nm-high (deep) protrusions and pits with nanometer lateral dimensions revealed on the surfaces of TGS crystals are characteristic of their microrelief. These microrelief details can be formed either as a result of crystal cleavage in the ferroelectric phase or the mechanical action of a cantilever onto the crystal surface. These two-dimensional formations are relatively stable and genetically related to the layer structure of the ferroelectric phase of TGS crystals.

Thermostimulated electron emission from polar cleavage of a triglycine sulfate crystal

This paper reports the results of experimental investigations into thermostimulated electron emission from the positive and negative cleavage surfaces of a ferroelectric triglycine sulfate crystal. It is shown that the current density j of emission from the negative surface is universally higher than that from the positive surface over the entire range from room temperature to the Curie point. The shape of the j(T) curves substantially depends on the degree of natural unipolarity of the studied samples. The results obtained are discussed in the framework of the mechanism of field electron emission from the surface electronic states.

Simulation of the poling of P(VDF-TrFE) with ferroelectric electrodes based on the Preisach model

In this paper, a multi-layered ferroelectric composite is analyzed by using the concepts of the classical Preisach model to describe each constituent material. The results obtained are compared to D-E measurements made in the poling of polyvinylidenefluoride-trifluoroethylene (P(VDF-TrFE)) copolymer film sandwiched between ferroelectric triglycine sulfate crystal (TGS) electrodes. In general, the computer simulations are in good agreement with experimental results.

Far IR excitation of longitudinal optical phonons in triglycine sulphate

In the parts of the Far IR (FIR) spectrum where Ferroelectric Triglycine Sulphate (TGS) is transparent for a given direction of the electric vector , the forced transverse vibrations that can be excited in that direction are shown to couple slightly with the Longitudinal Optical (LO) vibrations propagating along the wave vector (wave normal) of the FIR wave. Very clear LO phonons FIR transmission spectra at quasi-normal incidence with zero transmission sharp lines can thus be obtained at low temperature with thick samples, while classical spectra of Transversal Optical (TO) phonons are obtained with thin crystal plates. This coupling seems a second order effect, quite new, applicable to all low frequencies LO phonons of TGS and probably other crystals of low symetry. On the opposite, no coupling has been detected with an other direction than the vector.

Nonclassical high- and low-temperature behaviour of ferroelectric triglycine sulphate (TGS)

A very simple model of the free energy containing only two components P 2 and | P| δ+1 is proposed for the TGS ferroelectric. Assuming the values, γ=1, δ=3.17, of the exponents γ and δ determined from the susceptibility experimental data above T c, it is shown that the offered non-Landau model represents the TGS system nearly exactly above and below T c. The following values, 1.85, 0.46 and 2.2 of the basic critical invariants Q, β and Γ +/Γ − are forecasted, respectively. They are shown to be very close to their experimental counterparts. Various power laws above and below T c of the polarization and the susceptibility as functions of temperature or electric field are derived. The existence of other invariants connecting the polarization and the susceptibility above and below T c is predicted. The values for the suggested TGS model are compared with the Landau ones. A method to determine the exponent β from simultaneous measurements of polarization and susceptibility maxima at constant fields above T c is put forward.

Stochastic resonance in ferroelectric Triglycine sulfate

Stochastic resonance is a phenomenon that occurs in nonlinear systems, whereby a weak periodic input is amplified by an additional noise. We observed stochastic resonance in ferroelectric Triglycine sulfate (TGS). Below the Curie point there exist two domain states which are separated by an energetic barrier. The material is driven by small periodic signals that do not cause switching. There are different ways to prove the occurence of stochastic resonance in a bistable system: (i) The response of the system at the input frequency shows a maximum at a special noise level. (ii) An improvement of the signal-to-noise ratio may be registered. Additionally we observed that in ferroelectric TGS there exists a dependence of the response amplitude on the direction of variation of the noise. Increasing the noise from a very low level yields a lower maximum response than decreasing the noise. This may be caused by pinning of domain walls.

Higher order ferroic properties of TGS monocrystals

It follows from symmetry consideration that ferroelectrics should possess ferroelastoelectric properties also. The form of ferroelastoelectric domains of uniaxial «pure» ferroelectric triglycine sulphate (TGS) is determined. The effects of the influence of uniaxial mechanical pressure on dielectric hysteresis loops of TGS single crystals are observed. Pressure applied in y-direction decreases height of saturated hysteresis loops (case of high ac-voltage) and increases height of non-saturated loops (case of low ac-voltage). In both cases coercitive field decreases with the pressure increase. Such a behavior may be connected with ferroelastoelectric properties of TGS crystals when uniaxial pressure produces favorable conditions on the domain wall motion.

Temperature dependence of low field switching and coercive field in ferroelectric TGS

The temperature dependence of the maximum switching current density j m=j(tm) has been investigated for ferroelectric triglycine sulfate (TGS) at low fields (1kV/cm<E m<2kV/cm) under almost linearly rising pulses, being E m = E(tm) the field value at which the maximum switching current occurs. Increasing temperature above room temperature shows an intermediate zone between the two different switching behaviors already reported, which is intimately connected with the presence of a small bias in the sample. We discuss the meaning of coercive field in a ferroelectric in connection with the observed switching behavior.

NONLINEAR AMPLIFICATION EFFECTS IN A PERIOD-DOUBLING SERIES RESONANCE CIRCUIT

The influence of small near-resonant perturbations on the period-doubling bifurcations in a nonlinear series resonance circuit has been investigated in detail. The series resonance circuit contains ferroelectric triglycine sulfate (TGS) as nonlinear capacitor. If the temperature of the TGS-crystal is below the Curie-temperature this dynamical system is a good experimental realization of a Duffing-like oscillator with double-well potential. The depth of the double-well potential may be changed easily by temperature variation of the TGS-crystal. Variation of the amplitude of the driving voltage in the order of magnitude of the coercive field strength and the frequency of the driving voltage in the range of domain relaxation can be used to tune the system towards period-doubling bifurcations. An additional near-resonant perturbation has been introduced into the system by amplitude modulation of the driving voltage. The observed effects (small signal amplification, shift of the bifurcation point, multiple-side peaks around odd harmonics of half the driving frequency) are compared to theoretically derived results. They are well understood on the basis of the center manifold analysis taking into account nonlinear effects in the normal form of the period-doubling bifurcation.

Physical origin of the dynamical central peak in ferroelectric triglycine sulfate

The picosecond time-resolved spectroscopy is carried out to clarify the physical origin of the central peak that has been reported in uniaxial ferroelectric triglycine sulfate $({\mathrm{NH}}_{2}{\mathrm{CH}}_{2}\mathrm{COOH}{)}_{3}\ensuremath{\cdot}{\mathrm{H}}_{2}{\mathrm{SO}}_{4}$ (TGS). An ultraslow relaxational mode with a relaxation time $\ensuremath{\tau}=5--8 \ensuremath{\mu}\mathrm{sec}$ is reported as a real-time signal intensity $I(t)$ and is assigned to a thermal relaxational mode. This assignment is based on the fact that the diffusion constant evaluated from $\ensuremath{\tau}$ agrees well with the thermal diffusivity measured by heat-pulse method. The discovered mode, the thermal relaxational mode, is proved to be the physical origin of the reported central peak of TGS from the anisotropic anomalous behavior of the signal intensity at time origin $I(0).$

The coercive field conception for triglycine sulphate ferroelectric

The susceptibility hysteresis loops have been measured in ferroelectric triglycine sulphate (TGS) for very low electric field linear changes rates v= dE/ dt. The electric field values E jp ± T corresponding to susceptibility jump have been found at various temperatures. No dependence E jp ± on v has been observed in the interval 2 V/ mm per hour < v<250 V/ mm per hour. A modification of the polarization reversal process model has been proposed.

Microscopic characterization of low-field switching in ferroelectric triglycine sulfate

Low-field (&amp;lt;1 kV/cm) switching has been investigated for thin plates (0.06&amp;lt;d&amp;lt;0.15 cm) of triglycine sulfate by means of field pulses with a linear rise time. The dependence of the maximum current density, jm, with the field value Em at which this maximum occurs is jm≅B1(Em−Ecw1)3/2, for 0.3&amp;lt;Em&amp;lt;0.5 kV/cm, and jm≅B2(Em−Ecw2), for 0.5&amp;lt;Em&amp;lt;1.0 kV/cm. This is satisfactorily explained taking into account the dominant role played by sidewise and forward domain wall motion, respectively.

Thermal relaxation dynamics in TGS studied by time-resolved spectroscopy

The ultra-slow thermal relaxational mode has been newly found in uniaxial ferroelectric triglycine sulfate (NH2CH2COOH)3 · H2SO4 by the time-resolved spectroscopy. Typical relaxation time τ of the mode is in the time region of 5 ∼ 8 μsec. The thermal diffusivity D th evaluated from τ shows the remarkable anisotropic anomaly. This anomaly is successfully explained by the anisotropic polarization fluctuation enhanced near the structural phase transition of uniaxial ferroelectrics.

Anisotropic Thermal Relaxation Dynamics in TGS Studied by Impulsive Stimulated Light Scattering

An ultraslow relaxational mode with a relaxation time τ= 5 ∼8 µsec is discovered for the first time near the phase transition temperature T c = 48.5°C in uniaxial ferroelectric triglycine sulfate (NH 2 CH 2 COOH) 3 ·H 2 SO 4 using time-resolved spectroscopy. The physical origin of the mode is assigned to be thermal relaxation, because dominant anisotropic anomalous behavior can be observed in the Bragg-diffracted mode intensity at time origin I (0) and can be well explained by the anisotropic anomaly of the thermal expansion coefficient α and the anomaly of the specific heat at constant stress C X . The thermal diffusivity D t h evaluated from τ also shows the anisotropic anomalous behavior. This behavior is successfully interpreted by the anisotropic polarization fluctuation characteristic of the structural phase transitions of uniaxial ferroelectrics.