Features of infralow-frequency polarization relaxation processes in LiNbO3 single crystals

The dielectric response of lithium niobate single crystal in ac fields with amplitudes E of 3.74 to 13.1 kV cm^?1 is investigated at frequencies of 1 and 10 Hz in the temperature range of 70 to 200°C. The increase in effective dielectric permittivity ?_eff′ and the effective dielectric losses ?_eff″ is found to be associated with the formation of short-radius Nb _Li ⁴⁺ polarons at temperatures T > 130°C and their contribution to polarization relaxation in a LiNbO₃ crystal.     

Dielectric study of natural inyoite in the frequency range from 10−1 to 107 Hz and the temperature range from −50 to 140°C

For the first time, the method of dielectric dispersion in the 10^?1–10⁷ frequency range is applied to study temperature the dependences of permittivity, conductivity, and dielectric modulus of natural inyoite in the temperature range from ?50 to 140°C. An anomalous increase in the parameters under consideration is observed at temperatures between 87 and 98°C. According to thermal gravimetrical measurements, this range is characterized by an anomaly resulting from a partial loss of crystallization water.     

Dielectric behaviour of cellulose acetate-based polymer electrolytes

The present work deals with the findings on the dielectric behaviour of cellulose acetate (CA) and its complexes consisting of ammonium tetrafluoroborate (NH₄BF₄) and polyethylene glycol with a molecular weight of 600?g/mol (PEG₆₀₀) that were prepared using the solution casting method. The highest ?? obtained for CA-NH₄BF₄ film was 2.18?×?10^?7 S cm^?1 and enhanced to 1.41?×?10^?5 S cm^?1 with the addition of 30?wt.% PEG₆₀₀. The dielectric behaviours of the selected samples were analyzed using complex impedance Z*, complex admittance A*, complex permittivity ?*, and complex electric modulus M*-based frequency and temperature dependence in the range of 10?Hz?C1?MHz and 303?C363?K, respectively. The variation in dielectric permittivity (?? _r and ?? _i) as a function of frequency at different temperatures exhibits a dispersive behaviour at low frequencies and decays at higher frequencies. The variation in dielectric permittivity as a function of temperature at different frequencies is typical of polar dielectrics in which the orientation of dipoles is facilitated with the rising temperature, and thereby the permittivity is increased. Modulus analysis was also performed to understand the mechanism of electrical transport process, whereas relaxation time was determined from the variation in loss tangent with temperature at different frequencies.     

Dielectric and calorimetric studies on 1BC1EPOPB feroelectric liquid crystal having a large spontaneous polarization

Experimental investigations on the ferroelectric liquid crystal, R-4′(1-butoxycarbonyl-1-ethoxy) phenyl 4-(4-octyloxy phenyl) benzoate (1BC1EPOPB) of large spontaneous polarization (P _S(+) = 240?nC?cm^?2), using dielectric and calorimetric techniques, are reported. The temperature range of 25.0–125.0°C has been chosen for dielectric measurements. Dielectric dispersion studies are carried out in the temperature range 45.0–75.0°C and in the frequency range 2?Hz to 2?MHz for the smectic A, smectic C* and smectic X phases. A new phase called ‘smectic X’ has been found around 56.3°C. The transition temperatures identified by the dielectric dispersion studies for different phases and those given by DSC techniques are in close agreement.     

Investigation of the temperature dependence for the spectra of supercooled water in the middle infrared

The temperature dependence of the bending ν₂, combination ν₂ + ν _L , and stretching (ν₁, ν₃, 2ν₂) absorption bands in the infrared spectra of supercooled water with a temperature-change step Δt from 2 to 2.5°C was studied using an advanced infrared Fourier spectrometer. It was found that the frequency of the maximum of the stretching absorption band (2700–3700 cm^?1) decreases with the reduction of the water temperature from ?0.5 to ?5.0°C. The frequency of the maximum of the combination absorption band (2130 cm^?1) increases with the reduction of the water temperature in a range from ?3.0 to ?5.0°C. The frequency of the maximum of the absorption band of bending oscillation (1640 cm^?1) is invariable with a reduction of the water temperature from ?0.5 to ?5.0°C.     

Some dielectric properties of monoclinic lysozyme crystals

The frequency dependences of the dielectric loss tangent and the magnitude of the impedance for monoclinic lysozyme single crystals and the solution used for preparing the crystals were investigated. The measurements were performed in the frequency range 1–10⁷ Hz under exposure of the crystals at a temperature of 25°C, cooling to ?20°C, and subsequent heating. The analysis of the experimental dielectric properties of the crystals demonstrated that drying of the crystals at room temperature in air initially led to the removal of “free” water with the content approximately equal to 65% of the total content. Further drying resulted in the removal of “bound” water. The solvent contained in the crystals (～26 wt %) was frozen at a constant temperature of approximately ?6.5°C. The permittivity of the dehydrated crystal at high frequencies was considerably higher than that of ice.     

Electrodynamic properties of nanoporous silicon in the range from terahertz to infrared frequencies

The dielectric response (conductivity and permittivity) spectra of a series of nanoporous silicon samples prepared by anodization of low-resistivity single-crystal silicon are measured, for the first time, using terahertz and IR spectroscopy in the frequency range 7–4000 cm^?1 at room temperature. The spectra obtained are analyzed in terms of the effective medium theory with a size-dependent dielectric response function of nanoinclusions and averaged dielectric characteristics of the surrounding medium. The geometric and dielectric characteristics of silicon nanoinclusions are determined. The dielectric properties of inclusions are found to be affected by nanosize effects, namely, carrier scattering at crystallite boundaries and a broadening of the band gap due to quantum confinement. The spectra of the samples prepared by adding iodine to the electrolyte exhibit a resonance at frequencies of 150–300 cm^?1. The nature of the resonance can be associated with the presence of chemisorbed iodine on the surface of porous silicon. Possible mechanisms responsible for the changes in broadband conductivity and permittivity spectra of single-crystal silicon upon transformation into a nanoporous structure are discussed.     

Phase evolution and effect of pre-heating temperature on the characteristics of PZT thin films grown by using a triol sol--gel route

Lead zirconate titanate (PZT) films were fabricated on Pt(111)/Ti/SiO₂/Si(100) using the triol sol--gel method. The effect of the pre-heating temperature on the phase transformations, microstructures, electrical properties and ferroelectric properties of the PZT thin films was investigated. Randomly-oriented PZT thin films pre-heated at 400°C for 10?min and annealed at 600°C for 30?min showed well-defined ferroelectric hysteresis loops with a remanent polarization of 26.57?µC?cm^?2 and a coercive field of 115.42?kV?cm^?1. The dielectric constant and dielectric loss of the PZT films were 621 and 0.0395, respectively. The microstructures of the thin films are dense, crack-free and homogeneous with fine grains about 15–20?nm in size.     

Diffusion von Protonen (Tritonen) in Eiskristallen

The diffusion coefficient of tritons in ice crystals has been measured at different temperatures between 0°C and ?35°C. The applied method excludes any surface diffusion. The absolute value of the diffusion coefficient at ?7°C was determined as 2·10^?11 cm²/sec (±10%) and the activation energy as 13,5 kcal/mole (±8%). The activation energy of proton (triton)-diffusion is therefore consistent with the activation energy found for the dielectric and mechanical relaxation of protons in ice. The importance of this consistency relative to the diffusion mechanism is discussed.     

Correlation of dielectric properties,Raman spectra and calorimetric measurements of β-cyclodextrin-polyiodide complexes (β-cyclodextrin)2 ·BaI7 ·11H2O and (β-cyclodextrin)2 ·CdI7·15H2O

The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)₂·BaI₇·11H₂O and (β-CD)₂·CdI₇·15H₂O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba²⁺ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm^?1, 170?cm^?1 and 165–166?cm^?1 are due to the charge transfer interactions in the polyiodide chains.     

Effect of Ni(II) substitution on phase stabilization electrical properties of BICo(III)VOX.20 oxide-ion conductor

The BICO_0.20–xNI_xVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10^?4?S^?cm^?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔE_LT. However, the local minimum high-temperature conductivity, σ₆₀₀?°C?~?2.26?×?10^?2?S^?cm^?1 for x?=?0.10, coupled with a local maximum value of ΔE_HT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures.     

Anomalies of dielectric properties of vinylidene fluoride-trifluoroethylene copolymer films

The temperature dependences of the real and imaginary parts of the complex permittivity of vinylidene fluoride-trifluoroethylene copolymer films at temperatures ranging from ?40 to 140°C are determined in the frequency range 10^?1–10⁸ Hz. An analysis of the experimental data has demonstrated that the behavior of the dielectric characteristics of the copolymer in the course of heating to temperatures above the ferroelectric phase transition point and during subsequent cooling differs substantially. In the latter case, the high-frequency dielectric response exhibits properties characteristic of relaxor ferroelectrics. The observed features are discussed in terms of the competition of two mechanisms associated with the short-range and long-range forces.     

Possible mechanisms of dielectric relaxation of liquid water and calculation of the temperature dependence of the complex permittivity of water

The spectra of the complex dielectric permittivity and absorption of water (H₂O) in the frequency range 0–1000 cm^?1 are calculated for a wide temperature interval. Using the method of autocorrelation functions, the dielectric response of dipoles rotating in potential wells of three types is found. The majority of dipoles (about 90%) rotate in a deep and comparatively narrow potential well, whose profile resembles an upside-down hat. Such a potential models a molecular structure with strongly bent and/or broken hydrogen bonds. The hat model describes the complex permittivity in the low-frequency (Debye) range and in the range 300–1000 cm^?1. The remaining dipoles (～10%) execute harmonic vibrations of two types: rotational vibrations about the equilibrium direction of a hydrogen bond and translational vibrations along this direction. These types of motion yield the dielectric response in the frequency range 10–300 cm^?1. This response is described by the Lorentz lines in terms of the harmonic oscillator model and the truncated parabola model. The hat–harmonic oscillator–truncated parabola composite model provides good agreement with experimental spectra. The lifetimes of the three types of motion considered are about 10, 0.2, and 0.05 ps, respectively. They characterize (i) tetrahedral translations of molecules accompanied by their rotations, (ii) librations of dipoles in the hatlike potential well, and (iii) elastic interactions of hydrogen-bonded molecules. Based on data of independent methods of investigation, it is concluded that the temperature 300 K is a singular point with respect to the properties of liquid water.     

Fourier transform infrared spectroscopy to detect thermal degradation of vegetable and chrome-tanned leather

Abstract

The present experimental study determined the thermal degradation stages for vegetable and chrome-tanned leathers (goat and sheep) at 90, 100, and 130?°C by using Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis. Infrared spectra revealed that a temperature of 90?°C affected the adsorbed water band at 3400?cm^?1. Moreover, this temperature slightly reduced the vibrations of amide II and amid III (1340?cm^?1) confirming the preliminary decomposition of protein folds, but it is worth noting that the aliphatic side chains remained stable at this stage of aging. At 100?°C, there was a sharp rupturing in the phenolic-OH bond and side-by-side N–H vibrations decreased dramatically. The peak decomposition occurred at 130?°C, where the amide I and amide III intensities significantly increased, which can be considered indicative of protein unfolding. Those changes are substantiation of protein denaturation. Thermal analysis demonstrated that thermal aging significantly reduced the required temperature for the process of oxidation. The oxidation occurred at 217?°C in goat sample aged at 90?°C. Nevertheless, the reference sample suffered from oxidation at about 220?°C, while with increasing aging temperatures (at 100 and 130?°C), endothermic reactions were observed. Such reactions are usually associated with protein denaturation.     

Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1?×?10¹² to 2?×?10¹⁵ cm^?2, corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si–Si and C–C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8?dpa (i.e. ion fluence of 3?×?10¹⁴ cm^?2). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8?dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 °C up to 1500 °C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 °C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 °C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.     

Modified relaxor–PbTiO3 piezoelectrics for high temperature applications

In this study, Pb_{1? x} (Yb_1/2Nb_1/2)_0.515Ti_0.485O₃?x{(2SrO?+?BaO)/3} [PYNT–SBx] compositions with x?=?0.00–0.05 at the rhombohedral side near the morphotropic phase boundary were investigated. The SB substitution for Pb²⁺ in PYNT was found to increase the tetragonality, but greatly reduce the Curie temperature (T_c ) and broaden the dielectric permittivity maximum. The temperature dependence of the relative permittivity follows a Curie–Weiss law above the deviation temperature (T_D ) at high temperatures for the SB-doped PYNT. The optimized properties with a piezoelectric coefficient of 610?pm?V^?1, maximum dielectric constant (ε _max) of 25,000 (at the T_c ?=?315°C and 1?kHz), and a remnant polarization (P_r ) of 33?µC?cm^?2 were obtained in PYNT–SB0.04 ceramics.     

Terahertz dielectric spectra of (Ba,Sr)TiO<Subscript>3</Subscript> thin films

Reflection and transmission spectra of Ba_0.7Sr_0.3TiO₃ films with thicknesses of 36 and 800 μm on the MgO substrate are measured in the frequency range from 8 to 1000 cm^?1 at room temperature. The dielectric parameters of the film material are derived using the simulation method. The dependence of the permittivity on the film thickness is determined. It is found that the absorption spectrum of the substrate strongly affects the calculated dielectric spectra of the film material. It is demonstrated that the simulation should be performed with the inclusion of the dielectric losses in the substrate in the subphonon frequency range.     

Chemical,optical, and electrical characterization of Ga2O3 thin films grown by plasma-enhanced atomic layer deposition

Thin Ga₂O₃ films were grown on Si (100) using trimethylgallium (TMG) and oxygen as the precursors through plasma-enhanced atomic layer deposition. The depositions were made over a temperature range of 80–250?°C with a growth per cycle of around 0.07 nm/cycle. Surface self-saturating growth was obtained with TMG pulse time ≥20?ms?at a temperature of 150?°C. The root mean square surface roughness of the obtained Ga₂O₃ films increased from 0.1?nm to 0.3?nm with increasing the growth temperature. Moreover, the x-ray photoelectron spectroscopy analysis indicated that the obtained film was Ga-rich with the chemical oxidation states Ga³⁺ and Ga¹⁺, and no carbon contamination was detected in the films after Ar⁺ sputtering. The electron density of films measured by x-ray reflectivity varied with the growth temperature, increasing from 4.72 to 5.80?g/cm³. The transmittance of Ga₂O₃ film deposited on a quartz substrate was obtained through ultraviolet visible (UV–Vis) spectroscopy. An obvious absorption in the deep UV region was demonstrated with a wide band gap of 4.6–4.8?eV. The spectroscopic ellipsometry analysis indicated that the average refractive index of the Ga₂O₃ film was 1.91?at 632.8?nm and increased with the growth temperature due to the dense structure of the films. Finally, the I-V and C-V characteristics proved that the Ga₂O₃ films prepared in this work had a low leakage current of 7.2?×?10^?11 A/cm² at 1.0?MV/cm and a high permittivity of 11.9, suitable to be gate dielectric.     

Fluctuation theory of hydrogen bonding applied to vibration spectra of HOD molecules in liquid water. II. Infrared spectra: contour shape,integrated intensity,temperature dependence

The infrared spectra of HOD molecules in liquid water are calculated at constant density over the temperature range of 10 to 400°C from the statistical distributions of the vibration frequencies of water OH-groups determined previously from the experimental Raman spectra. Their shape and position are extrapolated over a wider temperature range. The dependence of contour shape and integrated intensity of the IR band on the frequency of its maximum, the first moment of a statistical contour and temperature are described numerically and analytically. Calculations are in qualitative agreement with all available experimental material and fitted quantitatively at a density of water of ～1?g?cm^?3. The success of the proposed model applied to infrared spectra supports once more the continuum treatment of liquid water structure.