Ferroelectric properties of doped triglycine sulfate crystals grown at negative temperatures

The effect of Cr³⁺ impurity ions on the dielectric and pyroelectric properties of triglycine sulfate crystals grown at temperatures below 0°C is studied. The Curie temperature T _C of the chromium-containing crystals is 0.2–0.4°C lower than that of the impurity-free crystals grown at conventional temperatures. A stable reproducibility of the results of the pyroelectric measurements for the crystals studied is established, which indicates that the polar state in crystals is stabilized by growth defects.     

Polarization switching of triglycine sulfate and deuterated triglycine sulfate single crystals irradiated with a high-current pulsed electron beam

The influence of high-current pulsed electron beams on the processes of polarization switching in triglycine sulfate and deuterated triglycine sulfate single crystals is investigated using the Barkhausen effect.     

Relaxation of the domain structure in triglycine sulfate and deuterated triglycine sulfate crystals in the course of polarization switching

Relaxation of the domain structure in triglycine sulfate and deuterated triglycine sulfate crystals is investigated using polarization switching (during which the domain structure is disturbed from an equilibrium state by a dc electric field) over a wide range of temperatures.     

Pyroelectric properties of some compounds based on protein aminoacids

Protein aminoacid-based compounds were synthesized, and their single crystals were grown. The dielectric and pyroelectric properties of the crystals were studied in the temperature ranges 80–340 and 140–340 K, respectively. It was established that three of the compounds studied (L-His(H₃PO₄)₂, L-TyrHCl, L-Ala₂H₃PO₃ · H₂O) are linear pyroelectrics, with their room-temperature pyroelectric figures of merit being close to those of ferroelectric triglycine sulfate crystals.     

Dielectric loss as an indication of the kinetics of the ferroelectric phase transition

The dependences tanδ(f, T) for triglycine sulfate and diglycine nitrate single crystals are investigated in the frequency range f = 1?2 × 10⁷ Hz at temperatures from ?150 to 50°C for triglycine sulfate and from ?150 to ?60°C for diglycine nitrate. The results are discussed in the framework of the model according to which two or more types of media with different dielectric properties are formed in the ferroelectric phase. The polar volumes of domains themselves and the volumes of domain walls with different symmetries are treated as individual media. The dependences tanδ(f, T) make it possible to separate the contribution of a particular medium and to trace its evolution with temperature. The results of the analysis of the relaxation properties confirm that the phase transitions lead to the formation of two media (the polar medium and domain walls) in triglycine sulfate and three media (the polar medium and two types of domain walls) in diglycine nitrate. It is demonstrated that the relaxation properties are not steady-state characteristics of the samples but depend on their prehistory.     

Acoustic emission upon spontaneous polarization in triglycine sulfate single crystals

We report on the results of analysis of acoustic emission (AE) under thermal action on a triglycine sulfate (NH₂CH₂COOH)₃ ? H₂SO₄ crystal. The triglycine sulfate single crystals grown from solution and not subjected to mechanical treatment are heated to a temperature above the Curie point (T_C = 49°C). During natural cooling of the crystal, a transition from the paraelectric to ferroelectric phase is accompanied by intense AE. In the temperature range ～28–30°C, an anomalous drop of the mean-square voltage in the AE signal is observed against the background of monotonic accumulation of AE events.     

Anisotropy of the Resonance Transformation of the Microhardness of Crystals after Their Exposure in the EPR Scheme in the Earth’s Magnetic Field

It is shown that the preliminary exposure of ZnO, triglycine sulfate, and potassium hydrogen phthalate crystals in ultralow crossed magnetic fields—Earth’s magnetic field and ac pump field—leads to a resonance change in their microhardness. The resonance frequency of microhardness peaks is determined by the classical condition of electron paramagnetic resonance only at certain orientations of the crystals with respect to the Earth’s magnetic field B_Earth. Rotations of all samples with respect to the direction B_Earth by angle θ reduce the resonance frequency in proportion to cosθ. The observed anisotropy has been attributed to the presence of their own local magnetic fields B_loc ? B_Earth in the crystals.     

Comparative study of the effect of low-dose gamma irradiation on phase transitions in single crystals of triglycine sulfate and its deuterated analog

The effect of low γ-radiation doses (< 0.5 MR) on the specific heat C _p of crystals of triglycine sulfate and its deuterated analog was studied using precision vacuum adiabatic calorimetry in the temperature range 80–350 K. Appreciable changes in the behavior of C _p of nominally pure and γ-irradiated crystals were detected near the phase transition temperature (T _c ), which decreased as the dose was lowered.     

Ferroelectric properties of triglycine sulfate crystals with a nonuniform distribution of chromium impurities

The specific features of the ferroelectric behavior of triglycine sulfate crystals with a nonuniform distribution of chromium impurities are analyzed. It is demonstrated that the dielectric hysteresis loops of the samples exhibit large shifts both along the polarization and electric field directions. The results obtained are well explained within the phenomenological approach with due regard for the gradient term in the expansion of the free energy. It is established that the unipolarity coefficient and the pyroelectric signal of nonuniform crystals remain virtually unchanged in multiple heating-cooling cycles.     

Effect of uniaxial stress on the birefringence of triglycine sulphate crystals doped with L threonine

The temperature and spectral dependences of the birefringence ??n _i of triglycine sulphate (TGS) crystals with L-threonine impurity have been investigated. Doping with L-threonine is found to reduce the temperature dependence of ??n _i of TGS crystals. The baric coefficients of shift of the phase-transition (PT) point, ?T _c /???m, are found to be somewhat smaller than those for pure TGS crystals, which is confirmed by the increase in the hardness of TGS crystals after doping. The temperature and spectral dependences of the combined piezoelectric constants ?? _im ⁰ have been calculated. The stepwise changes in all piezoelectric constants at the PT of doped crystals are found to be much smaller than those for pure crystals.     

Radiative color centers in doped sapphire crystals

Experimental and theoretical results of investigation of the spectral properties of sapphire (α-Al₂O₃) single crystals are analyzed. Crystals grown under different conditions, both nonactivated and activated with impurity ions of the iron group (Cr, V, Mn, Fe, Co, Ni), primarily with chromium ions, were investigated before and after irradiation with photons and high-energy electrons. It is shown that the impurity composition of crystals significantly affects the radiative and optical properties and the character of changes in the electronic state of impurities.     

Selective effect of a weak DC magnetic field on triglycine sulfate crystals

The effect of the selective influence of a dc magnetic field on the characteristics of nominally pure triglycine sulfate crystals was detected for the first time. A short (minutes) exposure to a weak magnetic field B₀=0.08±0.01 T caused long-term (hundreds of hours) changes in the spontaneous polarization, coercive field, Curie temperature, and permittivity of the crystal at the Curie point. The effect is selective in nature presumably because of the participation of hydrogen bond protons in the spin-dependent processes of the transformation of defect complexes in real crystals.     

Electron emission in ferroelectrics for different values of the coercive field

Results are presented of experimental studies of electron emission from single crystals of triglycine sulfate, nominally pure and doped with Cr³⁺. The relation between the parameters of the processes of switching and electron emission from ferroelectrics by a coercive field and the threshold field for the onset of emission is investigated. It is shown that the temperature and concentration dependences of the threshold field can be explained by the corresponding dependences of the coercive field. Fiz. Tverd. Tela (St. Petersburg) 41, 1675–1678 (September 1999)     

Nonlinear dynamics in an electrical circuit containing a ferroelectric

Nonlinear effects in a series oscillator circuit containing a ferroelectric capacitor are investigated as a function of the temperature and the amplitude of the applied field. A relation is established between the circuit parameters and the resonance shift in samples of a pure triglycine sulfate crystal and in samples containing chromium impurity ions. The observed effects are explained on the basis of a feature in the domain structure of the samples and the influence of point defects on it. Fiz. Tverd. Tela (St. Petersburg) 39, 918–919 (May 1997)     

Temperature dependence of the spin-lattice relaxation time for quadrupole nuclei under conditions of NMR line saturation

The contributions of different mechanisms of nuclear spin-lattice relaxation are experimentally separated for ⁶⁹Ga and ⁷¹Ga nuclei in GaAs crystals (nominally pure and doped with copper and chromium), ²³Na nuclei in a nominally pure NaCl crystal, and ²⁷Al nuclei in nominally pure and lightly chromium-doped Al₂O₃ crystals in the temperature range 80–300 K. The contribution of impurities to spin-lattice relaxation is separated under the condition of additional stationary saturation of the nuclear magnetic resonance (NMR) line in magnetic and electric resonance fields. It is demonstrated that, upon suppression of the impurity mechanism of spin-lattice relaxation, the temperature dependence of the spin-lattice relaxation time T₁ for GaAs and NaCl crystals is described within the model of two-phonon Raman processes in the Debye approximation, whereas the temperature dependence of T₁ for corundum crystals deviates from the theoretical curve for relaxation due to the spin-phonon interaction.     

Domain structure of triglycine sulfate family crystals according to the data of piezoresponse force microscopy and their macroscopic dielectric properties

The domain structure of triglycine sulfate (TGS) crystals, specifically nominally pure crystals and those with impurities (LADTGS+ADP, DTSG, and TGS:Cr), is studied by piezoresponse force microscopy (PFM). The measured macroscopic dielectric characteristics are compared with microscopic data on the domain structure of these crystals. The values of the spontaneous polarization, bias voltage, and dielectric permeability as a function of temperature ?(T) are shown to be in agreement with the PFM data. The anomalous behavior of the dependence ?(T) was observed for LADTGS+ADP crystals.     

Rearrangement of the domain structure of cobalt- and chromium-doped triglycine sulfate crystals

The paper reports the results of studies of repolarization and rearrangement of the domain structure of triglycine sulfate (TGS) crystals containing two impurities, cobalt and chromium. The introduction of these impurities hinders the repolarization of TGS crystals and causes their spontaneous polarization to decrease, the coercive field to increase, and displacement fields to form.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 63–66, April, 1991.     

Influence of the humidity on dielectric characteristics of porous aluminum oxide with inclusions of triglycine sulfate

The temperature dependences of the capacitance and conductance measured for samples of porous aluminum oxide films with inclusions of triglycine sulfate have been investigated. The character of these dependences obtained for the films treated in a humid atmosphere differs from that of the corresponding dependences measured for the initial porous Al₂O₃ matrix, bulk triglycine sulfate, and dried Al₂O₃ + triglycine sulfate composite. The observed changes are determined by the influence of the water adsorbed on the surface of the film and the water structured in pores of the composite.     

Impurity Luminescence of Alexandrite Crystals

The luminescence of alexandrite excited by a highcurrent electron beam is investigated. Its spectrum has bands of the impurity ions Cr³⁺ and of the Cr–Cr pairs and also the band at = 492–495 nm. In all of the crystals we have detected chromium ions distributed over two nonequivalent positions, differently in different crystals. It is shown that the color of the crystals and its change on illumination of the crystals with the light of different spectral composition depend mainly on the chromium ions and their distribution over crystalline positions. A noticeable effect of other impurity ions is noted for a number of crystals.     

Compositional dependence of the Curie temperature in mixed ferroelectrics: effective field approach

An effective field approach is used to investigate the compositon depedence of the Curie temperature T_C(x) for mixed ferroelectric systems of partially deuterated triglycine sulfate (TGS)_1−x(DTGS)_x, and partially deuterated triglycine selenate (TGSe)_1−x(DTGSe)_x. We found that the coupling strength between the two sub systems is weaker than the average value of the effective field within each system, this can account for the non-linearity of composition dependence of the Curie temperature in these mixed ferroelectric systems.