Triglycine Selenate Crystals Research Articles

Ellipsometric study of electronic excitations in triglycine sulphate and triglycine selenate crystals

AbstractThe real and imaginary parts of the pseudo‐dielectric susceptibility, 〈χ1〉(E) and 〈χ2〉(E), of triglycine sulphate (TGS) and triglycine selenate (TGSe) ferroelectric crystals have been obtained in the range 4–9.8 eV by spectroscopic ellipsometry using the Berlin Electron Storage Ring for synchrotron radiation source. A first maximum in 〈χ2〉(E) was found at E = 7.3 eV for both crystals and is attributed to the excitation of p‐electrons of oxygen. The spectra were measured at different temperatures in the range comprising the ferroelectric phase transition temperatures, 49 °C (TGS) and 22 °C (TGSe). Of note is the peak‐like behaviour in 〈χ1〉(T) and 〈χ2〉(T) near the phase transition temperature and a considerable decrease (about 50%) of the reflected light intensity IR in the range below the phase transition temperature (T < TC). The latter is probably caused by light scattering on the ferroelectric domain walls.

Dielectric losses behaviour under frequency and a.c. field amplitude variation in TGSe crystals

Dielectric losses in triglycine selenate crystals were studied in the frequency range from 20 Hz to 1 MHz for several a.c. field amplitudes. The peculiar shape of the temperature dependence of the loss factor D = tan δ reflects the character of the phase transition, which is very close to tricritical. In the range from 20 Hz to 10 kHz the temperature behaviour of tanδ is described according to the model presented previously for TGS crystals, adapted to the TGSe, taking into account the specific features of the phase transition. A low and a higher frequency relaxation band in D vs. frequency were found and a dip in D was noticed in the range of a few kHz for several temperatures near and below T C. The relaxation frequency attributed to domain wall motion increased rapidly, reached a maximum around 3 K below T C' and then dropped in relative value toward lower temperatures, as it has been observed in other ferroelectric transitions.

The electric susceptibility of strongly deuterated triglycine selenate crystals near the temperature of the first order phase transition

Abstract The temperature and electric field experimental dependences of electric susceptibility for deuterated triglycine selenate (DTGSe) with deuterium contents x ≃ 0.9 and x ≃ 1 are presented. The electric field (x ≃ 0.9) and temperature (x ≃ 0.9 and x ≃ 1) double hysteresis loops for susceptibility are shown. The influence of sample inhomogeneities as well as the amplitude of measuring electric field on the phase transition has been also ascertained. The deviations from Landau theory have been found.

Gamma-radiation and isotopic effect on the critical behavior in triglycine selenate crystals

Isotopic effects in pure and γ-irradiated triglycine selenate crystals were investigated using the specific heat ( C p) technique. The obtained results showed an interesting dependence of the critical behavior of C p on the deuterium content. With increasing content of deuterium, the character of the phase transition changed from a second order (γ-type) to a first order transition. After γ-irradiation, the behavior of C p around the phase transition region was essentially affected. The transition temperature, T c, decreased and Δ C p depressed, and the transition became broad. It was noted that the effect of γ-irradiation is opposite to the isotopic effect.

Dielectric properties of triglycine selenate crystals admixtured with VO2+ions

Abstract Dielectric properties of triglycine selenate monocrystals admixtured with VO2+ ions were investigated. This admixture was found to be responsible for an increase in spontaneous polarization, coercive field and Curie temperature as well as for a decrease in the maximum permittivity ϵmax.

Effect of deuteration on the phase transition of pure and Cr3+-doped triglycine selenate TGSe

Abstract Results of dielectric studies are reported in triglycine selenate crystals DTGSe, pure and admixtured with chromium ion DTGSe+ Cr3+. From these results and observations double hysteresis loops above the Curie temperature, the DTGSe and DTGSe + Cr3+ crystals are found to undergo a phase transition of the I-st kind.

Effect of Surface Layers on the Coercive Field, Spontaneous Polarization and Dielectric Constant of Triglycine Selenate

The coercive field and spontaneous polarization have been measured as a function of temperature (-10°C to 22°C) for different thicknesses (about 2 mm to 0.5 mm) of triglycine selenate crystals. The thickness dependent dielectric constant has also been measured at frequencies 1 kHz, 10 kHz and 100 kHz. The coercive field is found to be inversely proportional to the thickness of the sample. The spontaneous polarization has been found to decrease with decreasing thickness and the effect is most pronounced at smaller thicknesses. The results can be explained by assuming a single homogeneous surface layer of low dielectric constant. However, the numerical values of surface layer thickness estimated from the coercive field measurements are two order of magnitude higher than those derived from thickness dependent dielectric constant measurements.

Dielectric, piezoelectric, elastic properties and internal friction of TGSe crystals with large unipolarity

AbstractIn this work we have studied influence of temperature and external electric field on dielectric, elastic, piezoelectric properties and internal friction of D, L‐α‐alanine doped triglycine selenate crystals. Experimental result analysis allows to conclude that ferroelectric materials with stable physical properties may be created on doping crystals foundation.

Domain-Wall Orientations and Wall Energies in Ferroelectric Triglycine Selenate Crystals

Detailed observations of domain structure in triglycine selenate crystals have been made in special respect to the orientations of the 180° domain-walls by an improved powder-deposition technique. Two kinds of flat wall can be seen; one is parallel to the crystallographic (001) planes and another is to the (\bar201) planes. The angular dependence of the wall-energy density has been numerically calculated on the basis of the Zhirnov-type continuum theory. Two minima in the energy are obtained, each of which corresponds to the wall orientations observed experimentally. The numerical values of elastic stiffness, electrostrictive, dielectric constants and correlation-energy coefficients required for the calculation have been also determined experimentally. The theoretical and experimental results of wall orientations are discussed in comparison with those of triglycine sulfate crystals.

Influence of conditions for growing triglycine sulfate and triglycine selenate crystals on the nature of the change in specific resistivity

Influence of conditions for growing triglycine sulfate and triglycine selenate crystals on the nature of the change in specific resistivity