TGS Single Crystals Research Articles

Growth and characterization of l-lysine doped TGS and TGSP single crystals

Growth aspects of l-lysine doped TGS and TGSP single crystals from aqueous solution by a temperature reduction method have been investigated. The effect of dopant on morphology and crystal properties has been studied. Ferroelectric domain patterns have been observed on the b-cut plates of doped crystals. Powder X-ray diffraction analysis confirms the structure and change in lattice parameter values for the doped crystals. The presence of dopant in the crystal lattice has been qualitatively confirmed by FTIR analysis. The dielectric permittivity and spontaneous polarization values have been estimated and the Curie temperature is found to increase upon doping. Hardness measurements were carried out on the grown crystals.

Energy distribution of electron emission from l-α alanine doped TGS single crystals

Energy distribution measurements for electron emission from l-α alanine doped TGS single crystals which have shown considerable internal bias, induced by a drive ac electric field with an amplitude of 10 3–10 4 V/cm, have been carried out. The energy spectra observed for electron emission produced under negative charging of the emitting sample surface due to switching of the spontaneous electric polarization, differ from that detected for a positive one. The influence of internal bias on these energy spectra is also evidenced.

Electron emission from ferroelectrics

Electron emission from bare surface of TGS and BaTiO3 single crystals are presented and compared with emission from grid electroded surface. The correlation in time between emitted current and applied electric voltage is studied. Different regimes of electron emission are proposed. Interpretation of results of electron emission current versus thickness of the samples and geometry of the grid electrode is considered. Electron emission from PZT ferroelectric thin films is presented and the interpretation of a new electron emission peak is given.

Ferroelectric emission stimulated by AC field in the mode of temperature auto-stabilisation

The AC field-stimulated ferroelectric emission from TGS single crystals and BaTiO3 ceramics under conditions of Temperature Auto-stabilisation of Non-linear Dielectrics (TANDEL effect) is experimentally studied. Kinetics of the emission is found to be determined by the process of sample heating at switching the polarisation.

Effective conductivity of DTGS and TGS single crystals under ultra weak fields of low and ultralow frequencies

Comparative research has been carried out of dielectric properties (and with their help of conductivity) of DTGS and TGS single crystals under ultra weak fields (Eo = 0,2V.cm-1) of low (LF) and ultralow (ULF) frequencies (v = 104-10-1Hz) in the range of temperatures from 20° to 120° (including the phase transition (PT). There are reasons to think that the ULF conductivity of the DTGS single crystal in paraelectric phase is ion-jumping conductivity caused, most likely, by jumping of deuterons whose activation energy is -0,93eV. The conductivity of TGS single crystals in paraelectric phase, is apparently due to several carriers that make integrated contribution to the conductivity of a crystal on LF and ULF.

Modification of pyroelectric crystal TGS using thermodynamic theory

Based on the Devonshire thermodynamic theory, the relationship λ χ = Ps/C can be regarded as a method to increase the pyroelectric material figure of merit of ferroelectric crystals. Several modified TGS crystals doped with urea or co-doped with urea and other dopants have been grown. The effect of the urea dopant on crystal growth and pyroelectric properties was investigated. The pyroelectric figures of merit M ( λ ϵ ) of the doped TGS crystals are obviously higher than those of pure TGS. Furthermore, the variations of λ χ and Ps/C as a function of temperature for these doped TGS single crystals were measured, and analyzed according to the Devonshire thermodynamic model.

The analysis of domain boundaries dynamics of TGS single crystals under the AC-Fields of low and ultralow frequencies

The contribution of hysteresis and relaxational mechanisms of domain boundaries motion in low- and ultralow frequencies spectra of real (ε) and imaginary (ε') components of complex dielectric permittivity (ε*) of TGS single crystals in a wide interval of repolarization fields is investigated. It is revealed, that with growth of amplitude of repolarization fields the contribution of hysteresis mechanism of domain boundaries motion in ε* is increased, and with growth of frequency of repolarization fields the contribution of hysteresis mechanism of domain boundaries motion in ε* decreases

Dielectric response of some ferroelectrics at ‘low’ frequencies I

The dielectric response of ferroelectric PST ceramics and of TGS single crystals was measured in the seldom reported range 10−3-104 Hz. Their complex dielectric susceptance (ω) = X′(ω)—iX″(ω) shows, after removal of processes such as direct-current conductivity, Low-Frequency Dispersion and certain dipolar features, underlying regions of relatively ‘flat’ frequency dependence obeying the ‘universal’ fractional power laws u (ω) ∝ (iω n-1) extending over five to seven decades of frequency. The magnitude of the power-law exponent n depends weakly on temperature and on the magnitude of the permittivity and depends only slightly, if at all, on the ferro- or para-electric state of the sample. We note that this residual universal response is seen by us more clearly in ferroelectric materials than in any others. The significance of these results is discussed.

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.

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.

Growth and characterization of l-valine doped tgs single crystals

Dielectric and pyroelectric properties were investigated for L-valine (LV) doped triglycine sulphate (LVTGS) single crystals grown by a slow cooling technique from LV (10 mol% and 20 mol%) doped TGS aqueous solution. Extremely high permittivity maxima (e.g. Kmax = 376,531 at 100 Hz) were observed at the secondary phase transition temperature (Tc = 49°C), presumably related to specific hydrogen bonds created by the aliphatic LV amino acid dopant. In spite of its low incorporation, the L-valine dopant induces high pyroelectric coefficients (p = 1.671 μC/cm2 K at Tc) and generates a 0.2 kV/cm internal bias field in the mechanically stable 20% LVTGS single crystal. At both room and Tc temperatures the dielectric constants decrease, the pyroelectric properties increase with increasing LV concentration (K = 45.5, p = 85 nC/cm2K at 25°C in 20% LVTGS crystal).

Pyroelectric properties of valine doped TGS single crystals

Abstract TGS was grown by a slow cooling technique adding several kinds of dopants (10 and 20 mole% alanine, 10% alanine + LiVO3, 10% and 20% valine) to an aqueous solution. The temperature dependent pyroelectric coefficient, p and the spontaneous polarization, Ps, of doped-TGS crystals were measured to study the transition temperature, Pmax and room temperature pyroelectric coefficient depending on the dopants and to calculate the figure of merit, (p/K), (K is a dielectric constant). Furthermore, several pieces were selected to investigate the positional inhomogeneities of the same sample. Moderate figure of merit (p/K) was obtained in valine doped TGS because of low temperature dielectric relaxation around −10°C, although valine doped TGS has a three times higher pyroelectric coefficient (p = 1.671μC/cm2K) at transition temperature (Tc) than that of alanine doped TGS.

Dielectric properties of valine doped tgs single crystals

Abstract Several kinds of alanine, LiVO3 and valine doped TGS single crystals were grown from solution by a slow cooling method. Temperature dependence dielectric spectra were measured to study the variation of transition temperature, Kmax and room temperature dielectric constant depending on the dopants. Furthermore, several pieces were selected to investigate the positional inhomogeneities of the same crystal. D-E hysteresis loop measurements were done to check for the internal bias field (Eb ). The measurements did not show a high figure of merit (p/K) in valine-doped TGS because of a possible low temperature relaxation around –10°C, although it has three times higher pyroelectric coefficient than that of alanine at transition temperature (Tc).

Growth of TGS Single Crystals by Graded Neutral Gel Technique and their Characterization

Growth of TGS Single Crystals by Graded Neutral Gel Technique and their Characterization

Phase transition of TGS under variable uniaxial stress at fixed temperatures

Abstract The behaviour of hysteresys loops of TGS single crystals under variable uniaxial stress X (0–800 dyn/cm2) along the a, b and c. (|a,b) axes has been investigated at fixed tempreatures near the zero stress transition temperature, Tc(0), resulting in stress-induced ferro-paraelectric transitions. The cubic coefficient, ξ, appearing in the equation of state, E=χP+ξP3 decreases for X ‖ a, and x‖b, and increases for X ‖ c. with increasing stress, thus approaching the tricritical point in the latter case.

Far IR harmonic oscillators in triglycine sulphate at 7 K

Transmission spectra of very thick TGS single crystals (e.g. thickness 8 mm) observed in the Far IR at 7 K do not need a high spectral resolution and nevertheless give evidence of Lorentz oscillators with damping coefficients as small as those considered for water vapour at a pressure of 0.2 atmospheres.

Research on TGS single crystal growth with modulated structure

The experimental results of TGS crystal growth with modulated structure (periodic laminar of ferroelectric domains) is briefly discussed in this paper. The method used here is to add some DL-alanine additive in the solution of TGS and to apply the electric field during crystal growth, the direction of which is periodically varied. By using this method, TGS single crystals containing a nearly regular and flat periodic laminar structure of ferroelectric domains have been fabricated.

Phase transition of T.G.S.: T.E.M. and P.A

Abstract Nucleation of bismuth on TGS single crystals has been studied at different temperatures showing unlike characteristics above and below Tc. Decoration figures which may be ascribed to ferroelectric domains are observed at low temperatures. Moreover, Doppler broadening curves have been recorded and a sharp change in the positron behaviour is also noticed at Tc.

Study of the relaxation of the permittivity in doped and gamma-irradiated TGS single crystals

Abstract The change of the permittivity in gamma-irradiated and chromium and vanadgl doped TGS single crystals is investigated after switching of an applied d.c. electric field. Two types of the time dependence of the permittivity are observed. This behaviour may be correlated to real domain structure.

Dielectric properties and electrical conductivity of neutron irradiated TGS single crystals

The dielectric constant, spontaneous polarization, the pyroelectric activity and the electrical conductivity were studied for TGS samples exposed to low doses of fast neutrons. The results obtained are discussed within the frame of the thermodynamic theory of ferroelectricity. An appreciable change was observed in the value of α (which is related to the Curie-Weiss Law) while a slight decrease was noted in β with increasing doses of radiation. The electrical conductivity was measured in the ferroelectric transition region. Radiation first increased the conductivity then decreased it. The observed anomaly disappeared either by irradiation or by application of an external poling field. The results are discussed taking into consideration lattice defects found.