TGS Crystals Research Articles

Strange Thermal Expansion of Ferroelectric TGS in the Cryogenic Temperature Region

Recently a strange temperature dependence of the volume thermal expansion coefficient of TGS crystal has been found in the cryogenic temperature region. Therefore an electric field effect on the simultaneous measurement of the permittivity and the thermal expansion was examined under consideration of difference of a ferroelectric domain structure. The strange feature of the volume thermal expansion coefficient below 10 K was recognized again in the measurement without poling and this feature disappeared in the measurement with poling. This strange thermal expansion without poling might occur because of freezing the interaction between each area in the multi-domain state.

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.

Atomic force microscopy of the mirror cleavage surface of defect TGS crystals

The nanorelief of the mirror cleavage surface of triglycine sulfate crystals with various defect densities has been studied. Typical nanorelief features of both defect and clean (without artificial impurity) crystals are two-dimensional rounded bumps (dips) of equal height (depth) of about half the lattice parameter and sub-micrometer lateral sizes. The density, lateral size, and scatter of such 2D structures are several times larger for defect crystals than for clean ones. The correlation between the crystal defect density and the density and lateral size of 2D structures on the cleavage surface has been revealed. Conclusions are made about the defect origin of the typical nanorelief on the mirror cleavage.

Dielectric relaxation in TGS crystals doped with orthophosphoric and phosphorous acids

Polarization switching and temperature dependences of the complex permittivity of triglycine sulfate crystals doped with orthophosphoric and phosphorous acids are studied in the frequency range 100 Hz-1 MHz at temperatures of 140–340 K. It is found that, for a comparatively low solubility of the dopants (not over 1 mol %), doping of the crystals gives rise to a noticeable change in the parameters of the dielectric hysteresis loop, as well as in the magnitude and character of the temperature dependence of dielectric losses, thus implying an increase in the ferroelectric phase of the doped crystals of the activation energies and relaxation times of domain walls as a result of their interaction with the dopants.

Studies on the growth, structural, optical and mechanical properties of ADP admixtured TGS crystals

Abstract Ammonium dihydrogen orthophosphate admixtured triglycine sulphate crystals have been grown from aqueous solution by slow evaporation technique. X-ray analysis showed a slight variation in the lattice parameters for admixtured crystals. The optical transmission spectra indicated a wide optical transparency in the entire visible and near IR region. Dielectric measurements revealed in shift of Curie point to lower temperature with increase in dopant concentration. Microhardness studies have shown that the hardness decreases with increase in ADP concentration.

Growth and characterization of l-tryptophan-doped ferroelectric TGS crystals

Abstract Single crystals of l -tryptophan-doped triglycine sulphate (LTTGS) were grown by the low-temperature solution method. The effects of dopant on morphological changes were observed on the grown crystals. The grown crystals were characterized using powder X-ray diffraction (XRD), which shows that the LT TGS crystals are of monoclinic system. The presence of l -tryptophan in TGS was estimated qualitatively by Fourier transform infrared (FTIR) analysis. Microhardness studies carried out using Leitz Weitzler hardness tester at room temperature. The hysteresis studies were also carried out to understand the ferroelectric properties.

Ferroelectric Properties of TGS Crystals with Cr Concentration Gradient

In this paper certain peculiarities of the ferroelectric behavior of the TGS crystals with tailored non-uniform distribution of the impurity Cr3 + are considered. The dielectric hysteresis loops of the TGS:Cr samples were characterized by the large shifts both along the polarization P axis and along the electric field axis. It is established that the unipolarity coefficient and pyroelectric signal of the samples with the impurity gradient have remained stable at the repeated cycles of heating—cooling. The obtained results are explicated within the framework of the phenomenological approach taking into consideration the gradient term in the Landau-Ginzburg free energy.

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.

Electron Emission from TGS Crystals Grown on Seeds Exposed to Alpha Particles

The electron emission from triglycine sulfate crystal grown on a seed exposed to alpha-particles has been studied. It is shown that the emission manifests a behavior characteristic of unipolar material: in the region of rearrangement of domain structure and in the region of phase transition maxima there exist in the temperature dependence of emission current and their heights depend on the degree of unipolarity of a sample and the distance from it to the seed.

Relaxation of the nonequilibrium domain structure in TGS and TGSP crystals

The relaxation behavior of the nonequilibrium domain structure in nominally pure triglycine sulphate and triglycine sulphate doped with phosphorus has been investigated. A significant difference in the state of the domain structure formed as a result of slow and rapid cooling of crystals into the ferroelectric phase has been found.

On the ratio of Curie--Weiss constants in ferroelectrics undergoing second order phase transitions

Scaling hypothesis is used to construct the equations of state that provide the experimentally observed variety of the Curie--Weiss constants ratios (i.e., the ratios of the slopes between the temperature dependencies of inverse of susceptibility below and above the critical point) in uniaxial ferroelectrics. The results are exemplified by the TGS crystal and by the methylammonium salts MAPCB and MAPBB.

Investigation on the nucleation kinetics of antiferroelectric ADP admixtured ferroelectric TGS crystals

Induction period and interfacial energy have been determined for the aqueous solution growth of ammonium dihydrogen orthophosphate admixtured triglycine sulphate. It is observed that the induction period decreases exponentially with supersaturation and hence the nucleation rate increases with the increase of supersaturation. The solubility of synthesized ADPTGS has been estimated at different temperatures. ADPTGS has a positive temperature coefficient of solubility. Nucleation parameters such as radius of the critical nucleus, number of molecules in the critical nucleus and critical free energy change have also been investigated.

Effect of hydrostatic pressure on structural and electronic properties of TGS crystals (first-principle calculations)

First principle calculations of the effect of hydrostatic pressure on the structural and electronic parameters of TGS crystals have been carried out within the framework of density functional theory using the CASTEP code. The volume dependence of total electronic energy E(V ) of the crystal unit cell satisfies the third-order Birch-Murnaghan isothermal equation of state. For the pressure range of 5...5 GPa, the bulk modulus was found to be equal to K = 45±5 GPa. The relative pressure changes of the unit cell parameters were found to be linear in the range of 5...5 GPa. Crossing of the pressure dependencies of enthalpy corresponding to the ferroelectric and non-ferroelectric phases at P = 7.7 GPa testifies to the probable pressure induced phase transition in TGS crystal.

Criterion for identification of ferroelectric domains in TGS crystals from AFM images

Criteria for identification of actual (dynamic) domains and morphologically similar domain “memory” regions are proposed based on the study of various types of contrast of topographic atomic-force microscopy images of lenslike regions on the polar surface of TGS crystals. Inaccuracy in identification may result in further errors in estimating the parameters of the domain structure. The images of ferroelectric domains in the spreading-resistance mode that indicate directly the presence of conductive properties of the domain walls have been obtained for the first time.

Ferroelectric and Thermal Properties of L-Methionine Doped Triglycine Sulphate Crystal

L-Methionine doped TGS single crystals were grown using solution method. Ferroelectric hysteresis loop could be traced at room temperature under conditions of external electric field. The measurements in the present study were performed on single domain samples of 7 mm thick L-.Methionine doped TGS. X-ray diffraction (XRD) studies have been carried out to confirm the peak position. TGA and DTA studies were also carried out and the thermal properties have been analyzed. Electrical conductivity measurements were carried out at different temperatures and as a function of low and high frequency ranges. The conductivity of the L-Methionine doped TGS crystals was found to depend strongly on the frequency of the measuring electric field at different temperatures.

Sluggish Switching Process in the Triglycine Sulphate Crystal Exposed to the Transverse Electric Field

The measurements of a pyroelectric current generated by the TGS crystal previously exposed to the prolonged electric field E 3 parallel to the c-axis have been carried out. It has been found that the permanent transverse polarization P 3 ‖ c (i.e. perpendicular to the ferroelectric b-axis) appearing during the application of this field for the time interval Δ t can be expressed by the formula P 3 = P 3S [1-exp(-Δ t/τ)]. The saturation polarization level P 3S is at most only slightly dependent on the transverse field strength. On the other hand, the corresponding relaxation time τ markedly decreases as the field E 3 value is raised. A threshold transverse field of the order of 10 kV/m has been observed.

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.

Piezo-optic properties of TGS crystals doped with D-serine

The effect of uniaxial mechanical pressure along the main crystallophysical axes on the principal values of birefringence Δn i in TGS crystals doped with 5% D-serine is investigated. It is ascertained that the values of Δn i are rather sensitive to the action of uniaxial stresses. The temperature shift coefficients ∂T c /∂σm are determined for the phase-transition points. The temperature and spectral dependences of the combined piezo-optic constants π im 0 are calculated. The contribution of the secondary electro-optic effect to the changes in the birefringence and the piezo-optic constants of doped crystals is determined. It is found that the piezooptic constants π 23 0 and π 12 0 have the same values, which indicates a decrease in the anisotropy of the optical indicatrix of doped crystals under the action of uniaxial stress. The optical and deformation contributions to the relaxation effect of piezo-optical birefringence in doped TGS crystals are found.

The Effect of Isotopic and Isovalent Impurity on Low and Infra-Low Frequency Dielectric Response of the TGS and RS Model Crystals

The article presents the comparative results of dielectric responses of triglycine sulfate group and Rochelle salt group crystals. Dielectric properties of these crystals were studied under ultraweak probing electric field of low and infra-low frequencies at different temperature points. It is shown that the character of the dielectric response of these crystals is determined by the effect of isotopic and isovalent impurity.