Spontaneous polarization of triglycine selenate and triglycine fluoberyllate

Spontaneous polarization of Triglycine Selenate and Triglycine Fluoberyllate was investigated with crystals produced under various growing conditions. Spontaneous polarization of TGSe crystals grown at the Curie temperature is of the greatest value. The higher the supersaturation of the solution from which TGSe crystals were grown, the greater the spontaneous polarization. TGFB crystals grown at high temperatures are of greater value of spontaneous polarization than those grown at low temperatures.     

Band gap of triglycine selenate,triglycine fluorine beryllate,triglycine sulfate and its variation under γ-irradiation

The band gap for three ferroelectrics (triglycine selenate, triglycine fluorine berryllate and triglycine sulfate) is determined using an optic method. A shift of self-absorption edge towards longer wave lengths is observed when exposed to irradiation by γ rays with a dosage of ∽ (2 ÷ 7) · 10⁷ r as well as corresponding decrease of band gap. The observed changes are connected with the chemical nature of the studied substances.     

Domain structure and dielectric properties of TGS and DTGS single crystals depending on growth conditions

The influence of growth temperature and supersaturation of solution on domain structure and dielectric properties of TGS and DTGS single crystals was investigated. The qualitative and quantitative analysis of domain structures was carried out. The optimal growth conditions were found. It proves to be useful to arrange the measured values in table where lines correspond to growth temperatures and columns – to supersaturations for investigation of optimal growth conditions. The diagonal of extremal values exists in this table. The existence of optimal growth conditions explains in terms of interaction between domain and defect structures.     

Critical size of crystals growing under diffusion conditions for loss of polyhedral stability

A new expression is proposed for calculating the critical size for which, when reached, the polyhedral stability of a crystal growing under diffusion controlled mass transfer disappears. The well-known relationships for critical size are obtained as special cases of the proposed expression, for infinitely dilute solutions. In addition, it is shown that when the solubility increases, the critical size of the crystal must also increase, all other parameters remaining identical. Similar is the dependence of the critical size on the concentration.     

Critical behaviour and internal bias of TGS and isomorphous crystals depending on growth conditions

The critical behaviour of TGS and isomorphous DTGS, TGSe and DTGSe single crystals grown at various conditions was investigated. The growth dependences for ΔT in heating and cooling regimes and shift ΔT of the temperature of maximal permittivity were found. These dependencies were explained in terms of existence of internal biasing fields these being measured vs temperature.     

The secondary relaxation in the dielectric loss of glucose–water mixtures

We studied dielectric relaxation phenomena of glucose–water mixtures in the supercooled and glassy states at frequencies ranging from 0.1 Hz to 10 MHz. We clearly observed that as the water content or temperature decreased, the relaxation time difference between the α and the secondary relaxations increased and the relative relaxation strength between the α and the secondary relaxation decreased. We found that the effects of adding water or increasing temperature on the secondary relaxation are qualitatively similar to that of decreasing the rotation–translation (RT) coupling constant in the schematic mode-coupling theory [W. Götze, M. Sperl, Phys. Rev. Lett. 92 (2004) 105701].     

Derivation of the near-surface dielectric function of amorphous silicon from photoelectron loss spectra

The near-surface dielectric function ε(?ω) of hydrogenated amorphous silicon (a-Si:H) films has been derived from X-ray photoelectron energy-loss spectra, over the energy range 0–40 eV. Removal of low lying single-electron excitations is a prerequisite step to proceed to the derivation of the single plasmon energy loss function Im[? 1/ε(?ω)] due to collective electron oscillations. Several methods are compared to separate interband transitions from bulk or surface plasmons excitation. The shape of interband excitation loss in the range 1–10 eV can be described by a Henke function; alternatively, its removal using a sigmoid weighting function is a low-noise and reliable method. After deconvolution of multiple plasmon losses and self-consistent elimination of surface plasmon excitation, the single plasmon loss distribution allows recovery of optical (ellipsometry) data measured in the near-UV to visible range.     

Effect of some manufacturing conditions on the optical loss of compound glass fibers

The effect of the use of platinum crucibles and gas flow at glass melting and fiber drawing on the optical loss of compound silicate glass fibers have been investigated for the purpose of obtaining low-loss optical fibers. In concentrations of more than 50 ppm, platinum impurity dissolved into the glass from a platinum crucible increases the optical loss. The flow of oxidizing gas decreases the optical loss due to the Fe²⁺ ions. The flow of dry gas also decreases the absorption loss at 0.96 μm by water. The improvement based on these results lowers the total loss of clad fibers to 9.5 dB/km at 0.84 μm and 15 dB/km at 1.06 μm.     

Study of the surface heterogeneity of topographic and electric nature by atomic force microscopy by the example of triglycine sulfate

Triglycine sulfate crystals with an ideal (010) cleavage plane are used as model objects to reveal problems in interpreting atomic force microscopy (AFM) images of surfaces with nonuniform charge distribution. Specific microrelief features of two types are found: lenslike formations with different contrast and rounded protrusions/valleys of different size but fixed height. An analysis of their evolution with a change in temperature and under an electric field and mechanical impacts has made it possible to separate relief elements from the crystal domain structure. The interpretation proposed is confirmed by the multimode AFM data. The specific features of the images of dynamic domains and aged domains (which cannot undergo polarization reversal) are studied. The domain-wall width found in the AFM measurements depends on the technique used and the specificity of probe-surface interaction; it varies from 9 to 2000 nm. The most reliable data on the domain-wall width in triglycine sulfate crystals are provided by piezoelectric force microscopy, according to which the wall width does not exceed 30 nm.     

Triglycine sulphate single crystals growing doped with copper and cobalt ions and study of their dielectric properties

Growing conditions for TGS single crystals doped with Cu or Co ions are given in a table. ε and tg δ values in growth pyramids depend on crystal growing temperature and the incorporated impurity: Cu²⁺ ions increase the temperature hysteresis of the dielectric permeabilty. Incorporation of Cu²⁺ and Co²⁺ ions considerably decreases the difference in the values ε at 25°C in crystals grown at different temperature.     

Nanorelief of the natural cleavage surface of triglycine sulphate crystals with substitutional and interstitial impurities

Ferroelectric triglycine sulphate crystals (TGS) with substitutional (LADTGS+ADP, DTGS) and interstitial (Cr) impurities have been studied by atomic-force microscopy, X-ray diffraction, and X-ray fluorescence. The nanorelief parameters of the mirror cleavage TGS(010) surface have been measured with a high accuracy. A correlation between the crystal defect density in the bulk and the cleavage surface nanorelief is revealed at the submicrometer level.     

Study of dielectric relaxations in cellulose by combined DDS and TSC

In this work, thermally stimulated currents (TSC) analyses combined with dynamic dielectric spectroscopy (DDS) have been applied to the investigation of molecular mobility of cellulose. The correlation between results obtained by both methods allows us to attribute the low temperature DDS relaxation mode to the γ-mode resolved in TSC. The values of its activation parameters point out that the chain mobility remains localized. At high temperature, the various dielectric relaxation phenomena are separated by applying a recent analytical protocol. The comparison between the activation enthalpy values obtained by DDS and TSC leads to the assignment of the so-called α-mode to cooperative movements of polymeric sequences. The Arrhenius behavior of α-relaxation time is explained using the strong/fragile pattern. The influence of water content on secondary and primary relaxation modes was examined as well.     

Study of the possibility of growing germanium single crystals under low temperature gradients

The possibility of growing germanium single crystals under low temperature gradients in order to produce a dislocation-free material has been studied. Germanium crystals with a dislocation density of about 100–200 cm^?2 have been grown in a system with a weight control of crystal growth at maximum axial gradients of about 1.5 K/cm.     

Studies on electrical and the dielectric properties in MS structures

In this study, we investigated frequency dependent electrical and dielectric properties of metal-semiconductor (MS) structures using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics in the frequency range 100 kHz-10 MHz in the room temperature. The dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ) and ac electrical conductivity (σ_ac) were calculated from the C-V and G/ω-V measurements and plotted as a function of frequency. In general, ε′, ε″ and tan δ values decreased with increasing the frequency, while σ_ac increased with increasing frequency. Furthermore, the voltage and frequency dependence of series resistance were calculated from the C-V and G/ω-V measurements and plotted as functions of voltage and frequency. The distribution profile of R_S-V gives a peak in the depletion region at low frequencies and disappears with increasing frequencies. Also, series resistance values decreased with increasing frequency. The experimental results show that both frequency dependent electrical and dielectric parameters were strongly frequency and voltage dependent.     

Study of the domain structure of GASH single crystals and its correlation with their dielectric and switching behaviour

The domain structure topography of GASH single crystals is investigated by electron microscope decoration technique. A large variety of domain shapes was found in “young” crystals immediately after growth, whereas after one or more years of ageing the domain structure became coarse. The domain structure of the samples is related with their dielectric and switching behaviour.     

Structural organization of films based on polyaniline/polysulfonic acid complexes depending on the synthesis method

The optical properties and morphology of complexes based on polyaniline (PANI) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), depending on their synthesis conditions, have been characterized by UV-visible spectroscopy and atomic force microscopy. The dependence of the electron absorption spectra of PANI/PAMPS complexes and the surface topography of their films on the initiation way of PANI formation (chemical and enzymatic) and the use of promoters of aniline polymerization has been investigated. The aniline polymerization kinetics with and without polymerization promoters has been studied. All PANI/PAMPS complexes are found to have a nanocomposite time-stable structure.     

Stability of growth conditions and α-HgI2 crystal habit during growing by temperature oscillation method

On the basis of analysis of the experimental data, it is shown that:

• the crystal growth rate is mainly determined by diffusion in vapour phase;
• the limitation of the growth process by transport leads to an unremitting change of the growth conditions, being the cause of slowing down the growth and the change of the growth rates ratio of the crystallographically different facets, the latter evokes refaceting;
• the limitation of the growth by the transport process is the factor reducing the perfection of the structure and the maximum sizes of single crystals.

     

Effect of external forces on the dielectric and pyroelectric properties of strontium-barium niobate crystals

It is shown that high-temperature annealing of strontium-barium niobate crystals increases the mobility of domain boundaries in these crystals. This effect manifests itself in a shift of the peak of the effective permittivity of annealed samples to weaker fields. It is ascertained that the polarization of strontium-barium niobate crystals caused by annealing results in their more homogeneous single-domain state. The effect of Ce and Cr impurities on the polarization state of the surface layers in strontium-barium niobate crystals is considered.