Ferroelectric Triglycine Sulfate Crystal Research Articles

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.

Asymmetric polarization switching in triglycine sulfate crystals with free surface

Basic switching parameters (switching transient current, switching time, etc.) observed during electrical polarization reversal of undoped ferroelectric triglycine sulfate crystals with free surface are asymmetric. A comparison of the experimental data with the theoretical models of Fatuzzo [Phys. Rev. 127, 1999 (1962)], Pulvari, and Kuebler [J. Appl. Phys. 29, 1742 (1958)] shows that the classic models cannot to the fullest describe this type of polarization reversal. It is suggested that the asymmetric switching is caused by the difference in the field electron emission from a metal switching electrode and a ferroelectric crystal.

Effects of ultraviolet illumination on Fe3+- doped triglycine sulphate crystals and aqueous solutions

Abstract Holographic and optical spectroscopic investigations on ferroelectric triglycine sulphate crystals doped with iron are presented. Phase gratings can be recorded by interference of two ultraviolet laser beams in the 350 nm wavelength range. Ultraviolet irradiation induces a decrease in intensity of the Fe3+-absorption band centered at about 290 nm. The latter effect occurs in TGS:Fe3+ crystals as well as in iron containing triglycine sulphate aqueous solutions. A connection between different observed effects induced by UV light is suggested.

Phase gratings in Fe3+-doped triglycine sulphate single crystals recorded in the ultraviolet spectral region

Phase gratings have been recorded in ferroelectric triglycine sulphate crystals doped with iron by interference of two ultraviolet laser beams in the 350 nm wavelength range. The recording sensitivity increases with temperature and a diffraction efficiency exceeding 60% has been reached in a 5.5-mm-thick crystal after several hours of writing with intensities of 0.1 W/cm2. The photoinduced refractive index changes are anisotropic. The recording mechanism is not connected with the photorefractive effect and is believed to be due to the redistribution of hydrogen bonds leading to structural and refractive index modifications.

Solid state battery formation of triglycine sulphate and triglycine sulphate selenate

The d.c. electric field effect on ferroelectric triglycine sulphate (TGS) and TGS-Se crystals at high temperature above the Curie temperature shows the formation of a solid state battery. The current and the electromotive force of the battery are measured and their changes observed near the Curie temperature. Even if the electrodes are short-circuited the emf recovers almost to the same value.

Propagation of quasilongitudinal ultrasonic waves in the ferroelectric plane of TGS crystals

The velocity of quasilongitudinal ultrasonic waves in ferroelectric triglycine sulphate crystals was measured for 12 different directions of its propagation in the plane (010) for temperatures ranging from 273 to 343 K. Applying Christoffel's equation, six components of the elastic stiffness tensor describing the wave propagation and their temperature changes in the range studied were computed. Deviations of the normal vibration vector and the group velocity vector from the wave propagation vector were calculated, too. The wave was found to be “pure” for the directions close to the crystallographic axes a and c in the Hoshino system. Moreover, for the direction where the piezoelectric coefficient value was equal to zero, an additional minimum of deviation was observed. This value decreases with the temperature increase and, at the temperature (355±2)K, it is expected to run to zero. The anisotropy of the wave velocity changes at the transition from ferroelectric to paraelectric phase was determined. These changes were found to be equal to zero for the propagation directions making angles of −65° and +55° with the axis [001].

Topographic Study on Domain Boundaries in TGS. I

Intensity distribution on the section topographs for ferroelectric triglycine sulfate crystals containing an antiparallel domain boundary was calculated by using the dynamical theory of X-ray diffraction. The result shows an intensity peak corresponding to the domain boundary image. The intensity depends on the phase of the crystal structure factor. The calculated intensity distribution was compared with the results of the X-ray topographic observation reported by the same authors (Part I: J. Phys. Soc. Japan 44 (1978) 1266).

Attenuation of surface-acoustic-waves near the Curie temperature of ferroelectric triglycine sulfate

The temperature dependence of the attenuation of surface-acoustic-waves in poled ferroelectric triglycine sulfate crystals have been investigated in the vicinity of the Curie temperature. The absorption anomaly at low applied electric fields appears to have a relaxation character, and it is considerably larger than the corresponding anomaly in the case of bulk waves. The effect of the externally applied electric field is qualitatively similar to that observed in the bulk.

Orientational and long range effects in epitaxy

The mechanism of orientation in epitaxy has been studied on the electron microscope scale using as a model process the crystallization of silver chloride on ferroelectric triglycine sulphate (TGS) crystals both directly on the surface and via interfacial amorphous selenium layers. At the initial deposition stage, the AgCl crystals are distributed at random with respect to the TGS crystal surface. Orientation begins only at the coalescence stage, after the AgCl crystals have reached certain critical sizes. The AgCl crystals are at first positioned at an angle of 30° (±3°) to one another on the domains of both charge signs. Then, on the positive domains, reorientation of crystals by rotation solely in one direction takes place, i.e. for the first time a transition from a random distribution of initially generated crystals at first to one, and later to the other, azimuthal orientation is detected. Crystallization of silver chloride via amorphous Se layers does not cause any change in the mechanism of orientational effects. As a result, on the domains of both signs, including those coated with amorphous layers, network structures of AgCl crystals in an identical azimuthal orientation occur. The orientational and long range effects are explained in terms of an electrically active network structure existing in real crystal substrates. Nucleation takes place on the point defects of the substrate surface and on their “copies” on the surface of interfacial layers. The orientational effects are accounted for by linear elements of the network structure of the crystal substrates which interact with the particles of the crystallizing material after the latter reach certain critical sizes. Epitaxy as a whole is treated as a matrix-replicating process programmed in the electrically active real structure of the substrate.

New method for the visualization of domain and defect structure of ferroelectrics

AbstractA new method for the visualization of domain and real structure of ferroelectric triglycine sulphate (TGS) crystals on the scale of optical microscopy by means of decoration with auramine is developed. Auramine deposits on crystal surfaces as discrete particles about 2 microns in size and as a continuous layer, thus allowing both the domains as a whole and the various electrically active elements of the domain and real TGS structure to be visualized with high resolution. Due to decoration with auramine, the domain structure of TGS detected with a very high contrast; elements of the geometrical relief‐cleavage steps exhibiting different electrical properties are also revealed. Furthermore, it has been observed for the first time that the positive domains have sharp electrical boundaries, while the negative domains have erased boundaries. It has also been established that between the domains of opposite signs regions exist characterized by a very low electrical activity. Decoration of annealed TGS crystals which were rapidly cooled from the temperature of 150°C, i.e. above the Curie point (49°C) down to room temperature resulted in detection of new electrically active directions on the surface of the negative domains; these directions are likely to occur in the paraelectric state. The new method cannot only be applied to the study of the TGS crystals but can also be useful in investigation of other ferroelectrics.

Spontaneous strain in ferroelectric triglycine sulphate crystals: EPR studies of vanadyl impurities. Part II

In ferroelectric TGS crystals, EPR spectra of polar VO2+ impurities exhibit doublet splittings with unequal intensities on each of the 51V hyperfine lines. While the intensity ratio depends on vanadyl dipole relaxation in the spontaneous local field E(T), the corresponding strain in TGS lattices is considered to be responsible for the displacement of VO2+ axes. The strain tensor e determined from the VO2+ spectra is expressed as e = dE(T), where the tensor d consists of local strain coefficients at the impurity site. Unlike macroscopic piezoelectric strain coefficients defined for an externally applied field, these d-tensor elements indicated no temperature dependence. The function E(T) studied from VO2+ displacements and 51V hyperfine splittings is found to be proportional to the spontaneous polarization PS(T), being consistent with the previous result obtained from the doublet intensity ratio.

Internal field in ferroelectric triglycine sulphate crystals as studied by epr of V02 impuritiest

Epr spectra of VO +-doped triglycine sulphate crystals have indicated that the proton configuration in defective hydrogen bonds surrounding the impurity ions yields more than two differently oriented crystalline fields. On annealing the crystals at 80°C or above, these protons are rearranged in a stable configuration, resulting in simpler spectra. The stable VO2+ complexes have C2 symmetry, and the ligand hyperfine splittings due to a proton pair are partially resolved in their spectra. The observed anisotropics are slightly temperature dependent, implying that V02+ions execute a random motion with a small amplitude in the crystalline potential.VO2+ ions possess electric dipoles, which interact with the microscopic internal field at the trapping sites. In the ferroelectric phase, VO2+ spectra from well-annealed crystals exhibit a doublet splitting on each of the sl V hyperfine components. The equilibrium intensity-ratio of the doublet has been found to follow exp (ePs(T)lkT), where Ps(T) is the macroscopi...

VISUAL OBSERVATION OF FERROELECTRIC DOMAINS IN TGS

A ferroelectric triglycine sulfate crystal was illuminated by an intense CW laser beam; light scattered by the crystal at right angles to the beam was observed visually and photographed. The visible scattering column was found to be crossed by a series of bright lines oriented parallel to the ferroelectric axis whose appearance under various electric field and temperature conditions strongly suggest that they correspond to boundaries of ferroelectric domains. It therefore appears that this technique will permit direct observation of domain dynamics which, in the past, has been possible only with indirect techniques.

STIMULATED BRILLOUIN SCATTERING IN FERROELECTRIC TGS AND ROCHELLE SALT. EFFECT OF THE CRITICAL PHONON RELAXATION IN ROCHELLE SALT NEAR THE UPPER λ-POINT

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Effect of ferroelectric polarization on insulated-gate thin-film transistor parameters

The properties of a thin-film transistor deposited upon an oriented, ferroelectric triglycine sulfate (TGS) crystal have been evaluated in terms of the interaction between the remanent spontaneous polarization of the ferroelectric element and the space charge in the semiconductor layer. Experimental data suggests that this interaction results in changing the threshold voltage V 0 for the onset of drain current.